Sharon Redrobe BSc(Hons) BVetMed CertLAS DZooMed MRCVS
RCVS Diplomate in Zoo and Wildlife Medicine (Mammalian)
RCVS Specialist in Zoo and Wildlife Medicine
Head of Veterinary Services, Bristol Zoo Gardens, Bristol BS8 3HA UK
Honorary Senior Lecturer, University of Bristol.
Tel (00 44) 117 974 7339
Fax (00 44) 117 973 6814
Vet fax (00 44) 117 974 7380
email [email protected]
No portion of this document may be copied or distributed without the expressed
permission of Sharon Redrobe.
1
Clinical biology of small mammals
Sharon Redrobe BSc(Hons) BVetMed CertLAS DZooMed MRCVS
RCVS Diplomate in Zoo and Wildlife Medicine (Mammalian)
RCVS Specialist in Zoo and Wildlife Medicine
Appropriate handling techniques are essential to prevent injury to the animal or
handler when examining small mammals. Many can inflict and painful bite e.g. hamster.
Most pet rodents will resent being scruffed and should be gently cupped in the hand or
allowed to grip onto the sleeve of clothing. The tail should be held at the base to restrain
the small mammal. Care should be taken when restraining the gerbil by the tail as the
skin may slough. Chinchillas may shed large patches of fur when stressed or handled
roughly. This is known as ‘fur slip’. Hamsters have an abundant scruff and are able to
spin around and bite the handler when insufficient skin is included in the scruff. Rabbits
may kick with the powerful hindfeet and produce deep scratches on the handler. The
rabbit may also fracture or dislocate the spine, commonly at L7, if dropped or when
kicking out due to inadequate restraint. In many cases, therefore, it is preferable to use
sedation or a short anaesthetic to adequately restrain the small mammal for
examination. The use of isoflurane anaesthesia in small rodents allows for a rapid
induction and recovery, permits a thorough clinical examination and is arguably less
stressful for both animal and handler.
The clinical examination of the small mammal should include similar procedures as
those for the more familiar cats and dogs. Thoracic auscultation may be limited in very
small animals; the use of a paediatric or infant stethoscope is required in many cases.
Abdominal palpation may be limited although large masses e.g. enlarged uterus,
hepatomegaly may be detected. Core body temperature may be assessed using a rectal
thermometer or probe in some species. Aural thermometers are useful in medium sized
small mammals. The ophthalmoscope and otoscope may be used in the larger rodents
and rabbit to examine the eye and ear respectively. An oral examination is important as
most small mammal species have continuously growing teeth that are prone to
overgrowth and subsequent soft tissue problems. A full general anaesthetic is required to
thoroughly examine the oral cavity in these species.
The owner of the small mammal pet has increasingly higher expectations of the quality
of care for their pet. Despite their size limitations, using appropriate techniques it is
2
possible to thoroughly examine these smaller pets to the same high standard expected
of the more common domestic pets.
3
Biological data
Animal
Average
Lifespan
(years)
male 8
female 6
Sexual
Maturity
(weeks)
>3
months
Oestrus
Gestation
Period
Size Of
Litter
Age At
Weaning
Adult
Weight (g)
Approx.
Body Temp OC
IO Jan- Oct/Nov
28-32
2-7
6 weeks
38.5-40
Guinea Pig
4-7
15-16 d cycle
3-3.5 weeks
3
1- 2.5
1.5 - 2.5
every 4-5 days
every 4-5 days
every 4-5 days
60-72 (av.
65)
20-22
19-21
24-26
2-6
Rat
Mouse
Gerbil
M 8-10
F 4-5
>6
3-4
10-12
varies with
breed (1-8
kg)
750-1000
6-12
5-10
3-6
21 d
18d
21-28d
37
37.5
38
Syrian
Hamster
Russian /
Chinese
Hamster
Chinchilla
1.5 - 2
6-10
every 4 days
15-18
3-7
21-28d
1.5 - 2
6-10
every 4 days
19-20
3-5
21-28d
400-800
20-40
70-130
(M>F)
80-140
(M>F)
70-100
10 - 15
2 or 3
(1-4)
2-6
6-8 weeks
6-7 weeks
400-500
(M<F)
80-130
38-39
male 3
female 5
5-7
SP cycle 30-35d
Nov-May
SP cycle14d MarSep
IO Feb/Mar - Sept
111
Chipmunk
8
months
12
months
6-9
months
2-6 (up
to 10)
8 weeks
500-2000
38-40
Rabbit
Ferret
28-32
42
Key
IO = induced ovulation
SP = seasonally polyoestrus
4
38-39
37-38
37-38
37-38
1. Rodents
General anatomy
Dental formula 1/1 0/0 0/0 3/3. The incisors are chisel shaped, constantly growing and a
pigmented yellow colour. When gnawing the lower jaw moves forward so that the
incisors oppose each other but the molars do not. The cheeks are drawn in across the
diastema (the gap between the incisors and molars). This enables the rodents to gnaw
without wearing the molars or swallowing debris. Rodents exhibit coprophagy- the act of
eating faeces - to recover vitamins B and K.
Breeds/ colours
1. Syrian/ Golden Hamster large hamsters (100-150g), golden colour, now bred into
many varieties; selfs (one colour only e.g. cinnamon, cream, honey, white) and
marked / banded with white across back.
2. Chinese and Russian hamster dwarf varieties. Self, two colour varieties
3. Gerbil
agouti is natural colour- sandy brown , black tipped tail, white underside.
Also selfs and marked varieties.
4. Rat
self, hooded (coloured head, white body)
5. Mouse self, tan (one colour upper, tan underside), marked, long haired varieties
6. Guinea pig English- short smooth coat, Abyssinian- rosetted rough coat, Peruvian long haired. These breeds come in many colours e.g. self, agouti, tortoiseshell,
brindle.
7. Chinchilla natural colour is grey (silver), also available in white, brown velvet, black,
charcoal, pastels(!!).
Sexing rodents
Rat, mouse, gerbil, hamster, chipmunk
A papilla is seen in both sexes. In the male it is
the tip of the penis, in the female it is the urethral papilla. The distance between the anus
and the papilla (ano-genital difference) is greater in the male. The nipples are more
obvious in the female. The male hamster has obvious testes which can be seen from
above.
Guinea pig, chinchilla The female has a membrane between the urethral orifice and the
anus. The penis of the male can be extruded by gentle pressure and the testes can be
gently palpated either side of the anus. The retracted penis forms a Y shape in the
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prepuce. Beware; both sexes of guinea pig have an obvious pair of teats in the inguinal
area.
Methods of breeding
Rats, mice, chipmunk males and females may be housed together. A hareem system
may be used (one male, 2-4 females). Separating females before parturition avoids
mating immediately post-partum and prevents trampling of the young. Avoid handling of
young in first few days or may be eaten by dam. The new-born are altricial (bald, eyes
sealed, ears sealed, no teeth)
Gerbil
place in breeding pairs before 7-8 weeks old. Monogamous pairs formed for
life i.e. if one partner dies, the other may not breed with another. Male and female can be
left together with young as male assists with rearing young. The new-born are altricial.
Hamster
these animals are prone to fighting (female can be very aggressive) if not
introduced carefully. Use neutral territory or the female is introduced to the male’s cage
one hours before dark and supervised. Alternatively, male and female can be housed in
pairs from pre-puberty. The new-born are altricial.
Guinea pig one boar can be housed with 1-10 sows. In hareem style breeding programs,
the adults are housed together permanently and the young are removed at weaning.
Other systems remove the sow before parturition. The young are precocious (fully
furred, eyes open, teeth erupted) just like mini adults. The females should breed before
one year old. If they breed for the first time when older than this, the pubic symphysis
(pelvis) may have fused leading to dystocia 9problems giving birth). Best to breed first at
3 months old. At 24-36 hours before birth, the symphysis separates by 2cm approx. (a
thumb width), allowing accurate timing of the birth.
Chinchilla usually housed in single pairs and male removed at parturition. If more than
2 born, the third may die of hypothermia before mother can clean it dry. Females also
have difficulty rearing two and so best to remove and handrear extra young. The young
are precocious.
Husbandry
6
Rats, mice, hamsters
A large cage with sawdust, newspaper shredded, corn cob etc as deep bedding. The
animals will appreciate objects to gnaw e.g. dog chews, hard dog biscuit, cardboard
tubes, wood. A wheel enables vigorous exercise which these animals require.
Tunnel/stacking systems may be used for the smaller species. The animals should be
housed in a warm, dry, draught free room with good ventilation. Diet should include a
good quality rodent mix supplemented with fruit, vegetables and table scraps. These
animals (especially rats) are prone to obesity; this condition will reduce their lifespan. A
chamber or nest area should be provided. Water from a drinking bottle is preferred as a
bowl will quickly become contaminated or knocked over. Hamsters will hoard food in the
nest box and so this should be checked weekly for decaying food. ‘Fluffy bedding’ should
be avoided as this can become impacted in the cheek pouches and require an
anaesthetic for removal. Use shredded paper or straw instead. The animals should be
cleaned out 1-2 times per week as a minimum..
Gerbils
As above or (better) in a ‘gerbilarium’. A gerbilarium consists of a glass or plastic tank
half filled with moist peat, straw and sawdust to allow the animals to build many tunnels
and makes for an attractive exhibit. A wire lid on top is required and the water bottle may
be suspended from it. As gerbils produce little urine, this system only needs a thorough
clean out 4 times per year.
Chipmunk
These animals are easily stressed by people, noise and small cages and so should be
housed outside in an aviary where they have plenty of room to run and climb. Branches,
nestboxes, pipes/ tubes and deep straw/sawdust for foraging are required to prevent the
stereotypic behaviour of constantly chasing around a cage. These animals are very fast
so a double safety door system is recommended. If housed inside, the above system
requires a large indoor enclosure. Care; the frequency emitted from a television set
(even if switched off but still plugged in) is audible and loud to a chipmunk. The stress
can kill the chipmunk.
Chinchilla
7
These animal require a large cupboard type cage or an aviary. Branches and shelves for
climbing should be provided. These animals can develop caries and so sweets, sugary
foods should be avoided. The dense fur means that the animals can withstand cooler
temperatures but their lack of waterproofing means that they easily become hypothermic
when wet. Avoid damp conditions. They breed better when housed inside.
Guinea pig
Outside hutch commonly used for housing. Cannot tolerate very cold weather well.
Guinea pigs require vitamin C in the diet. This should be provided daily in the water at
1000mg /litre water (three times that amount for the pregnant guinea pig).
Handling And Restraint, Risks To Handler And Animal
Non aggressive animals can be gentle cupped in the hand and restrained by the base of
the tail. Take care with the gerbil which may slough the skin from the tail if handled
roughly. The rat, mouse, gerbil, hamster may be gently scruffed for injection or
examination by holding a flap of skin at the back of the neck. Hamsters have a lot of
loose skin and so can turn around in it and still bite if you have not grasped enough
scruff!! Rats can be held around the chest with the handlers thumb beneath the animal’s
chin to prevent biting and the hind quarters supported. Take care not to squeeze as it is
easy to suffocate the wriggling rat by accident. Handle guinea pigs using one hand
around the shoulders and one hand supporting the rump. The liver can be ruptured if the
guinea pig is handled roughly around the middle. Chinchillas can generally be scooped
up in the hands. The base of the tail may be held for restraint. When the chinchilla is
stress large amounts of hair may be lost (= fur slip) and bald patches may result.
Although the hair will regrow, the owner should always be warned about fur slip before
handling the animal.
2. Rabbits
Basic anatomy
RABBIT ANATOMY AND BIOLOGY (short version)
Rabbits are social, burrowing herbivores that are natural prey for a large number of
carnivores. As a prey species they have evolved to be constantly vigilant,
lightweight and fast-moving, with a highly efficient digestive system that enables
them to spend the minimum time possible above ground and in danger of capture.
8
For the same reason of not attracting predator attention, rabbit behaviour is not
florid and overt and relies heavily on scent.
Life expectancy of the rabbit is 5-8 years, but some individuals live to 10 years or
more.
Musculoskeletal system. The rabbit skeleton is light, making up only 7-8% of
bodyweight. The front limbs are short and fine, in contrast to the long and powerful hind
limbs. The plantar surface of the hind limb from the tarsus distally is in contact with the
ground at rest. The spine is naturally curved. Body conformation varies greatly
depending on the breed, from 1kg to 10kg, and from the squat or “cobby” shape of the
dwarf breeds to the lithe and lean (“racy”) Belgian Hare. Skull morphology can lead to
disease, especially dental problems, in some breeds. For example some dwarf breeds
have a mandibular prognathism which causes incisor malocclusion, and breeds with a
foreshortened skull seem predisposed to nasolacrimal duct and dental problems.
Great care must be taken when handling rabbits. A kick from the powerful hind legs can
result in lumbar vertebral fractures (usually L6/L7). The forelimb has five digits and the
hind limb four. The vertebral formula of the rabbit is C7 T12 L7 S4 C16. Thirteen thoracic
vertebrae are seen in some animals.
Dentition and oral cavity. The upper lip of the rabbit is cleft. The dental formula is 2/1
0/0 3/2 3/3. The incisors are used for grazing, and food is then passed to the back of the
mouth for grinding. Incisors have enamel layer only on the anterior surface, which wears
more slowly than the posterior surface, thereby maintaining a chisel shape for cutting
herbage. The vestigial second pair of upper incisors are located directly behind the first
pair and are known as “peg teeth”. All teeth are open rooted, long-crowned and grow
continuously. The cheek teeth are wider apart on the maxilla than on the mandible, and
the lower teeth grow faster than the upper. The oral commisure is small, and the oral
cavity long and curved. Cheek folds across the diastema make visualisation of the cheek
teeth difficult in the conscious
Eyes and ears the large eyes are located laterally (prey species) and rabbits have a
blind spot in the area beneath the mouth, so food is detected by the sensitive lips and
vibrissae. The lens is large and almost spherical, and the ciliary body is poorly
developed, so accommodation is limited. The retina is merangiotic, with the optic disc
9
lying above the midline of the eye and retinal vessels spreading horizontally out from it.
The optic disc has a natural depression or cup. There is no tapetum lucidum. A third
eyelid is present and the Harderian gland is located just behind it. This gland has two
lobes, the upper being white and the lower larger and pink in colour. The gland is larger
in males, especially during the breeding season.
Respiratory system Rabbits are nose-breathers (mouth breathing is a very poor
prognostic sign). The nose moves up and down in a normal rabbit (“twitching”) 20-120
times a minute, but this will stop when the rabbit is very relaxed or anaesthetised. The
glottis is small and visually obscured by the back of the tongue. Reflex laryngospasm is
common in the rabbit, which can complicate endotracheal intubation. The thoracic cavity
is small, and breathing is mainly diaphragmatic. The lungs have three lobes, and the
cranial lung lobes are small (left smaller than right). Large amounts of intrathoracic fat
are often present. The thymus remains large in the adult rabbit and lies ventral to the
heart, extending in to the thoracic inlet.
Cardiovascular system the heart is relatively small and lies cranially in the thoracic
cavity. The right atrioventricular valve has only two cusps. The rabbit aorta has
neurogenic rhythmic contractions.
Urinary system Rabbit kidneys are unipapillate. Urine is the major route of excretion for
calcium. Serum calcium levels in rabbits are not maintained within a narrow range, but
are dependent largely on dietary intake, with excess excreted via the kidney. Rabbit
urine is often thick and creamy due to the presence of calcium carbonate crystals. It can
also vary in colour from pale creamy yellow through to dark red (often mistaken for
haematuria by owners), due to the presence of porphyrin pigments thought to be derived
from the diet.
Reproductive system does have no uterine body, two separate uterine horns and two
cervices opening into the vagina. The vagina is large and flaccid. The mesometrium is a
major site of fat deposition.
Common pet Breeds
10
Dutch
small/ medium sized, black head and shoulders, white saddle (also other
colours to replace black) (1.5-3 kg)
New Zealand White large white albino rabbit (3-5 kg)
Lop often very large ears fall to sides, standard, giant and dwarf varieties (2-8 kg)
Dwarf
small rabbits (1-2kg), shorter ears, can be more nervous than other breeds
Sexing and Methods Of Breeding
Males have round penile sheath from which penis can be extruded. The large bald
scrotal sacs are obvious in the mature male. The female has slit-like opening. Begin
breeding of the doe between 4 and 6 months old. One buck can service 25 does. Doe
taken to bucks cage and left for ten minutes. Taken to another buck if not mated. Artificial
insemination is used commercially and is very successful.
Husbandry and diet
If housed outside the hutch should be at least large enough for the rabbit to stretch out in
all directions and rise up on the hind quarters. A separate bedding compartment with a
closed front should be bedded with straw. The run section with a wire front should have
a solid floor lined with newspaper, sawdust or straw. Water is supplied from a drinking
bottle and changed daily. Feed includes a small amount of commercial rabbit mix, lots of
hay daily (for roughage) and vegetables when available. Obesity, lack of fibre and lack of
exercise should be avoided. Rabbits are coprophagic. It is becoming increasingly
common to house rabbit inside. They can be rapidly litter trained but must be supervised
to prevent gnawing of electric cables.
Handling And Restraint, Risks To Handler And Animal
Rabbits rarely bite but have sharp claws which can inflict painful scratches on the
handler. Mishandling can lead to a fractured spine of the rabbit. The rabbit has powerful
hind legs and will attempt to kick out or escape if frightened. Pick up the rabbit firmly
around the shoulders or by the scruff. Support the hind quarters. Tuck the rabbits head
under your arm when carrying. Once the head is covered, the animal is calmer and if it
does struggle it will tend to push deeper under your arm. Place the rabbit back into the
cage rear end first to prevent kicking out at the handler. For restraint, hold the animal
with the rear end against your body and hands around the shoulders. To restrain for
11
intravenous injection into the ear veins, wrap the whole body in a towel, leaving only the
head exposed.
3. Ferret
General points
These carnivorous animals belong to the Mustelid family. Male are called hobs, female
are called jills. The young are called kits and a castrated male is known as hobbled!! The
colour variations affect the name used for the animal and can be confusing e.g. animal
which is brown with dark points is called ‘fitch’ or ‘polecat’ whereas a white/ albino colour
animal is called ‘ferret’. Other colours include ginger, silver mitt. The usual complaint
from ferret owners is that the animals smell, and the smell can be quite pungent. This is
due in part to the anal gland secretions, the sebaceous gland secretions in the skin. The
odour is much reduced in the neutered animal and when the animal is fed a proprietary
ferret diet and bathed weekly. They tend to have periods of great activity and then sleep
for a few hours.
Sexing and Methods Of Breeding
The penis can be extruded in the male. The testes are only descended in the mature
male during January- August. The female has a slit like vulva. When male and female
are introduced, mating will take place if the female is in oestrus. Mating is very
aggressive in ferrets with the male biting the scruff of the female. Mating can last for 1-3
hours. The female is an induced ovulator. If she is not mated oestrus may persist leading
to bone marrow suppression by the high levels of oestrogen. The female will become
anaemic, susceptible to infections and die. Unless females are required for breeding,
spaying is recommended to prevent this problem.
Husbandry and diet
Ferrets can be housed outside in secure sheds with pipes, ropes, hammocks, branches
and nest boxes. If housed inside they must be supervised as they can be destructive. A
cage for housing at night should be used. A proprietary ferret diet should be fed. This
ensures the ferret receives the correct concentration of protein, vitamin and minerals that
cat or dog food cannot provide. It also greatly reduces the smell of the ferret.
Handling And Restraint, Risks To Handler And Animal
12
Ferrets may nip and bite the handler, even when tame. Ferrets may be held with one
hand around the shoulders and neck, with a thumb under the chin to prevent biting, the
other hand used to support the rump. They respond well to gentle restraint with some
movement allowed. Ferrets can catch colds and ‘flu from people and can become quite
ill.
13
Suitability As Pets (Summary)
Animal
easy to handle
activity
bite
smell
Rabbit
yes but may kick out
daytime
rarely when tame
some
Guinea Pig
daytime
rarely when tame
some
Rat
yes but may squeal if
restrained
yes when tame
nocturnal
rarely when tame
yes
Mouse
yes when tame
nocturnal
rarely when tame
Gerbil
yes but fast and may
slough tail
?/ may be aggressive
daytime
nocturnal
if not handled
often
yes if woken up
yes (male
worst)
no
Russian ,
Chinese
Hamster
Chinchilla
?/ may be aggressive
nocturnal
yes if woken up
no
?/ fast, may fur slip
daytime
rarely when tame
no
Chipmunk
no, very fast
daytime
yes (nervous)
no
Ferret
yes but wriggles!
daytime but
sleeps a lot
rarely when tame
yes ?
(diet, sex)
Syrian
Hamster
SS= single sex group
pairs = male and female pair
14
no
Housing
where
social
group
inside,
group
outside
hutch
outside
group
hutch
inside cage SS
or pairs
inside cage SS
or pairs
inside cage, SS
gerbilarium
or pairs
inside cage, single or pairs
stacking
tunnels
inside cage, group
stacking
tunnels
outside
single or pairs
shed, inside
large cage
with shelves
outside
group
aviary
inside cage single or
at night
group
COLLECTION OF SAMPLES
1.BLOOD Maximum volume removed should not exceed 10% of circulating blood volume.
Species
Av. adult body
weight (g)
Av. adult blood
volume (ml)
Mouse
Gerbil/hamster
Rat
Guinea pig
Rabbit
25 - 40
85 - 150
300 - 500
700 - 1200
2000 - 6000
2.5
9
30
60
250
Maximum
sample volume
(ml)
0.25
0.5
3
6
25
Ferret
750 - 1000
50
5
15
Route
Lateral tail vein
Cardiac puncture
Lateral tail vein
Ear vein
Marginal ear
vein, jugular,
cephalic vein
Jugular or
cephalic vein
Sugar Glider (Petaurus breviceps)
Marsupial, native to New Guinea, Australia, rainforest or coastal forests: (Marsupaialia,
Phalangeroidea, Phalangeriae, Phalangerinae, Petaurus breviceps.
Nocturnal, arboreal, nests in leaf-lined tree holes with up to six other adults, young.
Gliding membrane (patagium) extends from fifth digit of forepaws to ankles. Gliding
distance ~50m
Tail, well furred, weakly prehensile
First and 2nd digit of hind feet are partially fused (syndactylous)
Body Temperature: 89.6°F
Does vocalize: Alarm “yaps”, screams
Natural Diet: Winter diet: gums of eucalypts, acacias. Rest of year, mainly insectivorous
Specialized incisors for gouging
Head/body length 120-132 mm, tail 150-480 mm. Weight (adult) ~ 100 grams
Captivity: breed throughout year, 2 litters/yr avg
Pouch: 2 teats, 2 offspring common
Gestation brief, ~16 days, migrate to pouch. Begin to leave pouch at 70 days,
independent at 17 weeks, but may remain in parental nest.
Body weight: 90-130 grams
Sexual maturity: ~ 8 months to 1 yr female, usually 12-14 months for the male The
female has the typical marsupial bilobed uterus with lateral vaginas and central birth
canal. Males have a forked penis, and mid-ventral scrotum. Males also develop a scent
gland on the forehead which they may also rub on the female’s chest. Males also have
scent glands on the chest, and anal glands. Both sexes scent mark territory. The female
just urine marks. Her scent glands are within the pouch. She will secrete and increase
marking to indicate breeding readiness to the male.
Life span in the wild: 7-8 years. Captivity: may live 12 - 14
Maximum recorded lifespan: 14 years
Duprasi (Fat-tailed Gerbil)
(Pachyuromys duprasi)
Native to the Northern Sahara Desert from western Morocco to Egypt, hamada (patches
of vegetation)
16
Head, body length: 105-135 mm; tail length: 45-60 mm, club-shaped
Pelage: yellow-gray to buffy brown above, underparts, feet: white. White spot behind
each ear. Tail: bicolored.
Well-developed claws front feet
Upper incisors: slightly grooved, open-rooted
Diet: insectivorous: (see Hedgehog diets, but can feed ad-lib unless animal becomes
obese) They will become obese on seed/grain based diets commonly sold for gerbils
and hamsters.
Auditory bullae, mastoids extend beyond foramen magnum
Weights range from 60-90+ grams
Sexual Maturity: ~2.5-3.5 months
Gestation period: 19-22 days
Litter size: 3-6 young
Life span: avg 3 years, recorded 4 yrs, 5 mos.
Blood draw sites, injection sites: same as for domestic gerbils, hamsters.
Degu (Octodon degus)
Atacama to Curico Province, northern and central Chile, West Andean slopes, elev to
1200 m
Head, body length 125-195 mm, tail length 105-165 mm.
Weight range: 170-300 grams
Upper pelage grey/brown, underparts creamy yellow
Tip of tail: black brush (may slip fur, chew off, section not replaced)
Fifth digit claw reduced, comblike bristles over the claws of the hind feet.
Active throughout year, diurnal. Vocalize with soft chortles, whistles
Construct burrows, territorial markers
Lives in colonies, females rear young in common burrow. Captivity: pair or groups
Natural diet: grass, leaves, bark, herbs, seeds, fruits, fresh cattle/horse droppings during
dry season, crops
Captive diet: grass hay, rodent blocks, occasional bits fruit, seeds, herbs
Stores food for winter.
May utilize chinchilla-dust baths
Breeds year round, multiple litters/yr
17
Sexual maturity: avg 6 mos
Gestation period avg 90 days
Litters: 1-10, avg 6.8 captivity
Eyes may not open for 2-3 days, birth weight: 14 grams
Wean at 4 weeks
Lifespan: captivity record 7 yrs
Diet: Rodent chow (1-5 cubes/week), grass hay, occasional small amounts fresh variety
of greens
Prairie Dog
(Cynomys ludovicianus)
“Black-tailed Prairie Dog”, Native to North America
Diurnal, do not hibernate, but may have dormant periods in inclement weather
“Bark” when excited, other vocalizations
Social, require companionship
Digging is primary activity, not agile climbers, but do like to try!
Many offered for sale - taken from wild-caught parentage. (screen for parasites, etc.)
Open-rooted incisors, cheek teeth
Nails: need frequent trimming, covers
Trigonal anal sac ducts
Adult body weight: 0.5-2.2 kg (males larger)
Hindgut fermenters
Sexual maturity: 2-3 yrs
Monestrous, seasonal (2-3 weeks Jan-March). One litter/year
Gestation: 30-35 days
Litter size: 2-10 (mean 5)
Weaning: 6 weeks of age
Ferret
Domestic pet ferrets, Mustela furo (sometimes called Mustela putorius furo), have been
domesticated for perhaps two or three thousand years.
18
Clinical facts
Rectal temperature 100-103 F (37.8 - 39.4 C), 101.9
Average Heart rate 216-250/min (225 average)
Respiration 33-36/min
Urine pH 6.5-7.5; mild to moderate proteinuria is common and normal
Blood volume 60-80 ml/kg, blood sample 10%
Blood sampling Jugular or cephalic vein
Healthy adult male is normally from 900 g to 2.25 kg, and a female from 40 g to 1.1kg.
Ferrets, especially males, normally gain up to 40% of their weight in the winter and lose
it again in the spring. a 5-year animal is considered to be "geriatric" and to require a
CBC [complete blood cell count] and a fasting blood glucose yearly.
Husbandry
Heat Ferrets don't tolerate heat well at all. Even temperatures in the 80s F (27 C) can
cause problems, and older ferrets can be even more sensitive.
Cold On the other hand, ferrets handle cold well. If they have full winter coats, they'll be
perfectly
happy living in 60 F (15 C). They can easily handle going outdoors in cold weather, and
many of them love to play in the snow.
19
Clinical biology of pet birds
Sharon Redrobe BSc(Hons) BVetMed CertLAS DZooMed MRCVS
RCVS Diplomate in Zoo and Wildlife Medicine (Mammalian)
RCVS Specialist in Zoo and Wildlife Medicine
CLINICAL ANATOMY
Birds have a thinner, more delicate skin than mammals, it may be almost transparent.
There is an epidermis, dermis and subcutis. The dermis is very thin with few blood
vessels and contains the feather follicles and their supportive muscles which run to
adjacent body prominences. Skin haemorrhage is rare. Bird skin has virtually no glands
other than the holocrine glands of the external ear canal and the uropygial gland,
however the whole skin surface of the bird can be regarded as a gland - it is lipogenic.
The uropygial gland is a large bilobed gland situated dorsally at the base of the tail, it is
common in birds, all psittacines except amazon parrots (Amazona spp) have one, it is
most developed in aquatic species and absent in ratites. The gland produced a lipoid
sebaceous material which the bird spreads over its feathers when preening. Perhaps
surprisingly the uropygial gland produces less than 10% of the plumage sebum, the rest
comes from the skin itself.
At the time of breeding many birds show a thickened dermis - the brood patch, this is
much more vascular and may bleed if injured, breeding birds will often pluck a patch
over this area. the subcutis is mainly loose connective tissue with fat.
Feathers are of epidermal origin growing around a feather follicle from the dermis, they
grow in distinct feather tracts and in several types depending on their location in the
body. Feathers are held in place in the ‘mature’ telogen phase at least partially by
tension of the non-striated feather muscles between follicles. The primary remiges (wing
feathers) arise from the manus, and the secondaries from the ulna. They are linked by
the interremigeal ligament which has some smooth muscle components, and the
primaries in particular firmly attached to bone. The tail feathers (remiges) are paired,
most birds have 6 pairs.
Hormone control of feather growth is not fully understood, in some species oestrogens
retard feather growth, in others they promote it, generally testosterone has little effect
and thyroxine initiates growth. Birds cannot rear and moult at the same time, generally
they moult before or after a rise in sex steroids.
Once adult plumage is reached most birds moult once a year after breeding, in most
species this occurs in waves through the feather tracts so that the bird is not made
flightless, although many water birds and flamingos do become flightless.
FEATHER TYPES:
Contour feathers
 Flight
20
 Body (includes the coverts covering the bases of the flight
feathers)
Others  Semiplumes - especially waterbirds
 Down - especially chicks, not in ratites, pigeons, and passerines
 Powder down - especially cockatoos, cockatiels & african greys
 Hypopennae - very large in ratites
 Filoplumes - not found in ratites
 Bristles
Avian Comparative Respiratory Anatomy and Physiology
All birds are not the same
• 8948 spp of birds compared with 4200 spp mammals
• sizes vary from the 1.6g, 2” Cuban humming bird to the 150Kg, 10’ African ostrich
• penguins flightless but swim at 20 mph; ostrich runs 100kph; swifts sleep, mate on
the wing and only land to lay eggs or die
• tracheal modifications; penguins divided into two channels; cassowaries have
subcutaneous coils under skin; swans coiled in sternum; whooping cranes as long as
the bird itself!
Comparisons between birds and mammals - anatomy
Bird
Mammal
no epiglottis
epiglottis
complete tracheal rings
open dorsally
voice from syrinx at bifurcation of trachea
vocal cords = vocal apparatus
lungs small and compact
large and expansible
anastomosing parabronchi
dead end alveoli
air sacs
none
no diaphragm
strong functional diaphragm
expansion of thorax via intracostal joint
via diaphragm + costovertebral joint
light pneumatic bones
heavy marrow filled bones
ribs attached to each other
ribs free
fusion thoracic and lumbosacral vertebrae
sacral vertebrae fusion only
Birds are not ‘weaker’ than mammals
• flight is expensive - flying budgerigar uses 1.5-3 x more energy than mammal running
in a wheel
• flight requires 13x bmr (20-30x in turbulent air); human athlete can maintain 15-20x
for a few minutes; but a swallow migrates 50h non stop over the Sahara
• man has incipient hypoxic collapse after 10 minutes at 6100m, mice comatose, house
sparrow flies at 7600m. Avian tissues are relatively resistant to hypoxia and do not
incur respiratory alkalosis- mechanism not known.
• Bar headed goose (Anser indicus) can fly straight from sea level to 9000m without
acclimatisation
• King penguins make dives to 500m without nitrogen toxicosis on descent or ‘the
bends’ on ascent - mechanism not known
21
However, birds are able to mask signs of illness until late stage of disease and rapidly
decompensate. Thus a vigorous clinical examination, diagnostic techniques and
supportive therapy must be used to assess and assist the avian patient.
22
Anatomy of the avian respiratory system
• two functional components; one for ventilation, one for gas exchange
• paired arytenoids, one constrictor + one dilator muscle
• oesophagus caudal and dorsal to larynx; air and food cross at pharyngeal chiasma
(electrocuted birds can swallow their larynx)
• 1o bronchus divides into 4 2o bronchi (medioventral, mediodorsal, lateroventral,
laterodorsal). All 4 groups connected to other 3 via parabronchi
• parabronchi = tubes off 2 o bronchi. Lots anastomoses. Internal diameter 0.5mm
humming birds, 2mm penguin
• parabronchi have atrial pockets (100um) leading to air capillaries (penguin 10um,
song birds 3um, mammal alveoli 35um) = site of gas exchange
• 6 inspiratory muscle, 9 expiratory muscles i.e. active inspiration and expiration
muscles (important for ventilation when in sternal recumbency)
• air sacs; cervical (1), clavicular (1), cranial thoracic (2), caudal thoracic (2),
abdominal (2)
• air sacs connect to 1 o and 2 o bronchi (direct connections); or to parabronchi
(indirect)
• pneumatic bones = pelvis, vertebrae, sternum, scapula, femur, humerus
Air flow
1st inspiration
1st expiration
2nd inspiration
2nd expiration
air to caudal air sacs
to parabronchi
to cranial air sacs
void
Paleopulmo and neopulmo systems
• MV-MD system + parabronchial connections to some LV = paleopulmo
• LV-LD system and connections to caudal air sacs = neopulmo (not in penguins, emu,
highly developed in passerines)
• paleopulmo - secondary bronchi to parabronchi to secondary bronchi on inspiration
and expiration = unidirectional flow
• neopulmo - towards caudal air sacs on inspiration, away in expiration = in and out
• continuous unidirectional flow = minimise dead space to trachea, allows cross
current blood flow = more efficient?
• does paleopulmo= efficient, neopulmo = less efficient system? penguins no
neopulmo (primitive?) but passerines are fast flyers with 75% neopulmo
Significance of respiratory anatomy to anaesthetic management
• restriction of ribs/sternal movement can lead to suffocation e.g. restraint, surgeons
hands/ instruments, heavy drapes, bandages
• in dorsal recumbency heart and liver compress lungs, GIT compresses air sacs. The
large pectoral muscle of Galliformes and Anseriformes hampers ventilation in dorsal
recumbency thus require intubation and forced ventilation
• rapid induction/recovery possible with gaseous anaesthetic agents
• if bird has peritonitis/ ascites, place in upright or feet elevated position to avoid
impairment of respiration and/or fluid entering lung
• complete tracheal rings - use uncuffed ET tubes
• airs sacs - intubate for gaseous anaesthesia
23
• avoid pneumatic bones for intraosseous fluids, care with amputation (lighten if under
gaseous anaesthesia), infection respiratory system to/ from bones
Physiology of the avian respiratory system
• birds extract 6% of the oxygen from the air, mammals take 4%; birds arterial CO2 is
30% lower than mammals (more efficient washout)
• respiratory cycle driven by CO2 intrapulmonary receptors, dermal nociceptors,
thermoreceptors (panting), chemoreceptors, baroreceptors (aorta) and
mechanoreceptors of respiratory tract
• some inhalant anaesthetics have a direct effect on the unique carbon dioxide
sensitive intrapulmonary chemoreceptors within the avian lung (Ludders Seaman Erb
1995)
• if increase CO2, increase respiratory amplitude (depth) not frequency
• high oxygen concentration may contribute to hypoventilation by depressing oxygen
sensitive chemoreceptors (Ludders Seaman Erb 1995)
• high metabolic rates
• penguin tissues are adapted to buffer lactic acid produced during anaerobic dives
hence can breath hold for long periods without ill effect
Significance
• if anaesthetise with high O2, will reduce CO2 concentration and will become apnoeic.
• spontaneous ventilation will recur once CO2 rises at end of procedure
• do not fast, just deprive of feed to empty crop or evacuate crop manually immediately
after induction.
• in theory cannot gas induce penguins although this is a practical method in the
authors experience.
• monitor respiratory depth not rate during anaesthesia.
Comparison of gas exchange mechanism avian vs. mammal
• paleopulmo system - cross current flow between bulk of parabronchial air flow and
blood in capillaries
• air decreases in oxygen along the parabronchus, thus blood becomes less
oxygenated, but blood is mixed from differing parts of the parabronchus
• thus end parabronchial gas has a greater ppCO2 and a lower ppO2 than arterial blood
• however mammals can only achieve equilibrium between end expiratory air and
arterial blood
• how do birds prevent ventilation perfusion mismatch?? Via smooth muscle in blood
vessels/ airways??
Comparison of the avian vs. mammalian respiratory system (for equivalent
bodyweight)
• avian trachea 2.7x length mammal = > resistance; BUT 1.3x radius = total same
resistance as mammal
• dead space bird 4x mammal; BUT bird 1/3 less respiratory rate and 4x tidal volume
per unit bodyweight
• weight of avian lung = weight of mammalian lung BUT avian lung 25% smaller
• thin blood gas barrier so total anatomical diffusing capacity for oxygen = 20% more
than mammal
(from King and Mclelland 1984)
24
Comparative cardiovascular physiology
• heart = 1-1.4% bodyweight sparrow only 0.5% bodyweight mouse, humming bird
1000 bpm.
• relatively large heart size and rate increases cardiac output e.g. cardiac output of
flying budgerigar = x7 dog at maximum exercise
• total peripheral resistance of birds < mammals BUT high cardiac output in birds so
high arterial blood pressure (140-250mmHg) so efficient O2 transport
Avian respiratory system- conclusions
bellows, continuous unidirectional flow, cross current parabronchial gas flow and blood
flow, parabronchi blood flow and air capillary flow, small diameter airways, large total air
diffusing capacity, high arterial blood pressure
= most efficient vertebrate breathing system
other important biological facts
• right jugular vein larger than left - use for blood sampling
• basilic vein subcutaneous on medial aspect elbow - use for i/v injections, sampling
• feathers replaced only 1-2 x per year - minimal pluck to reduce heat loss, avoid
disfigurement for long period, avoid plucking flight feathers
References
Concannon KT, Dodam JR, Hellyer PW. 1995. Influence of a mu and kappa -opioid
agonist on isoflurane minimal anaesthetic concentration in chickens. Am J Vet Res
56(6):806-811
Curro TG, Brunson DB, Paul-Murphy J. 1994. Determination of the ED%) of isoflurane
and evaluation of the isoflurane sparing effect of butorphanol in cockatoos (Cacatua
spp.). Vet Surg 23(5):429-433
Fitzgerald G, Cooper JE.1990. Preliminary studies on the use of propofol in the domestic
pigeon (Columbia livia). Res Vet Sci 49(3):334-338
Gentle MJ, Corr SA. 1995. Endogenous analgesia in the chicken. Neurosci Lett
210(3):211-214
Goelz MF, Hahn AW, Kelley ST. 1990. Effects of halothane and isoflurane on mean
arterial blood pressure, heart rate and respiratory rate in adult Pekin ducks. Am J Vet
Res 51(3):458-460
Greenlees KJ, Clutton RE, Larsen CT, Eyre P. 1990. Effect of halothane, isoflurane and
pentobarbital anaesthesia on myocardial irritability in chickens. Am J Vet Res. 51(5):757758
King AS, McLelland J. 1984. In Birds: Their Structure and Function. Bailliere Tindall 2nd
Edition. (Respiratory System pp110-144 and Cardiovascular System pp214-228)
Klein PN, Charmatz K, Langenberg J. 1994. The effect of flunixin meglumine on the
renal function in Northern bobwhite (Coliinus virginianus): an avian model. Proc Am
Assoc Zoo Vet pp128-131
Ludders JW, Mitchell GS, Rode J. 1990. Minimal anaesthetic concentration and
cardiopulmonary dose response of isoflurane in ducks. Vet Surg 19(4):304-307
Ludders JW, Rode J, Mitchell GS. 1989. Isoflurane anaesthesia in sandhill cranes (Grus
canadensis): minimal anaesthetic concentration and cardiopulmonary dose-response
during spontaneous and controlled breathing. Anaesth Analg 68(4):511-516
Ludders JW, Seaman GC, Erb HN 1995 Inhalant anesthetics and inspired oxygen:
implications for anesthesia in birds. J Am Anim Hosp Assoc Jan-Feb;31(1):38-41
25
Ludders JW. 1992. Minimal anaesthetic concentration and cardiopulmonary doseresponse of halothane in ducks. vet Surg 21(4):319-324
Paul-Murphy J. 1997. Evaluation of analgesic properties of butorphanol and
buprenorphine for the psittacine bird. Proc Assoc Avian Vet pp125
Pizarro J, Ludders JW, Douse MSA, Mitchell GS. 1990. Halothane effects on ventilatory
responses to changes in intrapulmonary CO2 in geese. Respir Physiol 82(3):337-347
Redig PT, Duke GE. 1976. Intravenously administered ketamine HCl and diazepam for
anaesthesia of raptors. JAVMA. 169(9):886-888
Schumacher J, Citino SB, Hernandez K, Hutt J, Dixon B. 1997. Cardiopulmonary and
anaesthetic effects of propofol in wild turkeys. Am J Vet Res 58(9):1014-1017
Seaman GC, Ludders JW, Erb HN, Gleed RD. 1994. Effects of low and high fractions of
inspired oxygen on ventilation in ducks anaesthetised with isoflurane. 1994. Am J Vet
Res 55(3):395-398
Sufka KJ, Hiughes RA, Giordano J. 1991. Effects of selective opiate antagonists on
morphine-induced hyperalgesia in domestic fowl. Pharmacol Biochem Behav 38(1):4954
Valverde A, Bienzle D Smith DA, Dyson DH Valliant AE. 1993. Intraosseous cannulation
and drug administration for induction of anaesthesia in chickens. Vet Surg 22(3):240-244
Williams TD. 1995. The Penguins. Oxford University Press
Avian husbandry
Psittacines
Housing
Cages for pet psittacines should be regarded as an unfortunate necessity for housing
the bird at night or when unsupervised. All the birds from the budgerigar to the macaw
can be trained to be handled safely, to ‘poop’ on command and to speak. These are
social animals and so the owner should be encouraged to tame the bird and treat it as a
member of the family as one would a dog. This greatly enhances the owner’s enjoyment
of the pet and the bird’s quality of life. Many of these species live for 20+ years and
should not be condemned to a cage for this long period. The cage should be large
enough for the bird to stretch out fully horizontally and vertically at the very least.
Perches of varying diameters (without sandpaper) will help to exercise the feet. The
cage construction should be strong enough to withstand the parrots bite, made of easily
cleaned, non toxic material, and provide easy access to the bird. Cage furniture should
not be provided at the expense of room for the bird. Ropes to secure toys should be
used in preference to chains to avoid leg and foot injuries. Many parrots enjoy
destroying toys, so dog chews, wood to strip, etc. are more beneficial than mirrors and
bells. Position the food and water bowls above perches to avoid soiling and change the
contents daily.
Feeding
The correct diet is crucially important to the health and longevity of the pet bird.
Unfortunately, malnutrition is very common (see; goitre, hypovitaminosis A,
hypocalcaemia) in the majority of patients. It is a vital part of the veterinary care of birds
to ensure a correct diet is fed. Soft food is commercially available and useful to increase
protein levels in the sick or breeding bird. It can be fed in small amounts in the normal
daily food.
26
Trees branches. These should be offered as environmental enrichment and many will
also eat the soft pith. Fruit trees and willow are safe to offer. Care should be taken to
ensure they haven't been sprayed with chemicals if collected from 'the wild'.
Cuttlefish bone is a valuable source of calcium and should be available all year round.
Clean, fresh water should be constantly available to all birds, and changed on a daily
basis. Some birds are not seen to drink much, especially if offered moist foods.
However, water should always be available.
Commercial bird food in a pelleted, complete form is now available in the UK e.g.
Kaytee, Harrisons, Pretty Bird companies. These pellets contain all the vitamins,
mineral, amino acids that the birds needs. Ideally, birds should be weaned onto these
diets. They are more costly than 'loose seed petshop' mixes but of course much better
nutritionally. For those owners that wish to keep costs to a minimum, 'wet mixes' can be
made up as below. Many owners, once trying to make up wet mixes, feel the pelleted
forms are more convenient.
Budgerigars
Budgies fed 'loose petshop seed mix' commonly present with nutritionally deficiencies.
Goitre is common is birds fed an unsupplemented mix. Proprietary seed mixes should be
fed which provide a balanced diet with iodine e.g. Trill: pedigree.
Parrots
To help eliminate boredom, feed can be offered as several meals spread over the day.
Sprouted pulses e.g. haricot beans, soya beans, green peas, mung beans, chickpeas,
maple beans, black-eyed beans and others from health food shops. The pulses and
seeds must be of 'human' edible quality- many loose pet shop mixes are of low grade
and nutritionally poor.
Fruits that may be offered include apples, plums, raspberry, blackberry, pear, peach,
grape, orange.
Vegetables include carrot, celery fed grated.
Peanuts and sunflower seeds when fed must be of quality for human consumption.
These provide a lot of fat and so should be limited to avoid obesity, especially in birds
which tend to obesity e.g. Amazon parrot.
If the bird becomes fixated on one type of feed e.g. peanuts, sunflower seeds, it is best
to gradually reduce those seeds to zero and only introduce those items again as
handfed treats.
Example diets
Amazon parrot - can become addicted to seeds and are prone to obesity. Must be feed a
good mix of fruit and vegetables and sprouted pulses (see above), fresh greens, and
very little wheat, maize, oats, buckwheat. Sunflower seeds and peanuts should only be
offered as occasionally treats.
Macaws - sunflower seed, pine nuts, maize, oats, wheat, buckwheat, rice, small seed.
Also soft food, fruit, some vegetables, mixed sprouted pulses, corn on the cob. Many
enjoy a little animal protein (chop bones).
General diet
A mix of 3 fruits, 3 vegetables, 5 nuts and seeds should be fed daily from one bowl
mixed in with a supplement (Avimix; Vetark). This provides a balanced diet and prevents
the bird choosing to eat only the ‘favourite’ foods. Tastes change with time so encourage
the feeding of such a varied diet constantly and mix so that bird has difficulty selecting
out ingredients.
27
Avoid chocolate, avocado, salt, alcohol, tobacco smoke, access to lead or zinc,
pesticides, overheated Teflon pans (poisonous).
Most pet bird species are opportunistic omnivores. Seed only diets contain excessive
amounts of fat and the multiple deficiencies noted in the table below.
Deficiencies and Clinical Conditions Associated with an All Seed Diet.
Factors Deficient in an all seed diet
Clinical Conditions Associated With
an All Seed Diet
Vitamins A, D3, E, B12 and K1
obesity
Riboflavin, pantothenic acid, biotin,
low body weight, poor growth
niacin, iodine, choline, copper, calcium,
polydipsia/ polyuria
iron, manganese, selenium, sodium, zinc crop impaction
Amino acids (lysine, methionine)
Diarrhoea
malabsorption, maldigestion
respiratory disorders
plumage abnormalities
skin disorders
skeletal disorders
neurological disorders
Reproductive disorders
Impaired immune response
Restraint
This section assumes to some extent that the bird is not used to being handled or
restrained. This is unfortunately the case with the majority of pet birds in the UK. Tame
birds may allow examination and auscultation with minimal restraint, but it is wise to
restrain the head. All the psittacines are able to inflict a painful bite and the claws of the
larger parrots can pierce the skin. Adequate restraint of the head and feet is therefore
essential.
• Birds have no functional diaphragm; air is drawn into and out of the lungs primarily by
sternal movements. Consequently any prevention of these movements will lead to
suffocation. Thus when handling a bird, never place the hands around the upper body of
the animal.
• Dim the lights and make calm purposeful movements to avoid excess stress to the bird.
Avoid chasing the bird as the heat generated will not be dissipated when restrained,
leading to panting, hyperthermia and collapse
• Smaller birds (budgerigars, cockatiels) may be held by the examiner, but a separate
handler is
Required for the larger birds to enable a complete examination to be carried out
• Remove as much cage furniture as possible without stressing the bird
• Small birds may be picked up from a perch. Bare hands or a cloth enable the tightness
of grip to be accurately gauged, gloves are not recommended. The use of a small towel
or cloth may be used to cover the bird whilst the head is located. This reduces the
chance of being bitten and restrains the bird more adequately as the cloth can be lightly
wrapped around the bird to prevent the wings flapping. The bird's head is grasped
between first and second fingers, the thumb and little fingers used to restrain the feet.
Wings can then be extended and held between the thumb and forefinger or using the
free hand.
28
•
The larger psittacines require a two handed approach. Tilt the cage to the side (having
first removed all cage furniture), allowing the bird to grip the bars with his beak. Using a
towel, grasp the bird around the mandible and neck. The towel can then be wrapped
around the bird to prevent wing injury and to restrain the feet. A piece of paper or towel
will give the bird something to chew on during the examination. Teasing the bird with
such an object often allows visualisation of the oral cavity.
Sexing
Budgerigar male has blue cere, female has brown
Cockatiel male has red cheek patches, female has pale orange, females have bars on
tail feathers
Larger parrots mostly sexually monomorphic (requires endoscopy or DNA sexing)
Restraint
Birds have no functional diaphragm, air is drawn into the lungs by sternal movements.
Restrain the head, avoid holding the chest, wrap/ restrain wings and feet. Gloves
are not recommended, as the strength of grip cannot be gauged.
Smaller birds (budgerigars, cockatiels) bare hands or a cloth enable the tightness of
grip to be accurately gauged,. The use of a small towel or cloth to cover and locate
head. This reduces the chance of being bitten and restrains the bird more adequately as
the cloth can be lightly wrapped around the bird to prevent the wings flapping. The bird's
head is grasped between first and second fingers, the thumb and little fingers used to
restrain the feet. Wings can then be extended and held between the thumb and
forefinger or using the free hand.
Larger psittacines require a two handed approach. Tilt the cage to the side (having
first removed all cage furniture), allowing the bird to grip the bars with his beak. Using a
towel, grasp the bird around the mandible and neck. The towel can then be wrapped
around the bird to prevent wing injury and to restrain the feet. A piece of paper or towel
will give the bird something to chew on during the examination.
Passerines
Housing
Mixed aviaries - outside with a shed for shelter with an outside enclosed flying area.
Many pairs of different species can be housed together
Breeding - kept in aviaries or in cages 50x40x40cm as pairs in breeding season.
Pets - kept in a long cage to permit horizontal flight. Perches of different heights and
diameter should be provided, and fresh water in an upright drinker changed daily.
Feeding the passerines are classed as seed-eaters. Commercial diets contain millet,
canary seed, rape, hemp, and alfalfa. Extra calcium should be provided, and fruit and
vegetables offered.
Sexing
canaries are sexually monomorphic. Male finches are generally more
colourful than the females. Male canaries usually sing well.
29
Basic Data
Common
Name
Budgeriga
r
Cockatiel
African
Grey
parrot
Amazon
parrots
Zebra
finch
Canary
Greater
Indian Hill
mynah
Pigeon
Country Of Origin
No Of
Eggs
4-6
Incubation
Time
16-18
Age At Maturity
Lifespan (approx.)
6 months
10-20 years
Australia
80
West and equatorial 450
Africa
5
3-4
18
26-28
6 months
4-6 years
10-15 years
Up to 40 years
West Indies, Central 400
and South America
Africa, SE Asia
12
2-4
23-24
4-6 years
Up to 40 years
6
12
6 months
5-10 years
Euroasia
India
15 - 25
170-260
4
2-5
14
14-15
1 year
2-3 years
6 - 16 years
12 - 25 years
Europe
350-550
2
17-18
5 months
Up to 15 years
Australia
Av. Weight
(g)
60
30
Imaging techniques in small mammals,
Sharon Redrobe BSc(Hons) BVetMed CertLAS DZooMed MRCVS
RCVS Diplomate in Zoo and Wildlife Medicine
RCVS Recognised Specialist in Zoo and Wildlife Medicine
[email protected]
Introduction to ultrasonography and radiography
Ultrasonography and radiography are complementary imaging techniques. In rare cases
one technique is used instead of another but more commonly both modalities are used
to maximise diagnostic information. Positioning is similar to the dog and cat for most
procedures.
Ultrasonography is an excellent modality for differentiating between fluid and soft tissues
and is therefore the diagnostic test of choice to investigate lesions of the bladder, heart
and uterus. Radiography requires contrast material to fully explore these organs.
Radiography is useful in determining the size, shape and position of organs within the
body and relative to each other as large areas of the body can be imaged.
Ultrasonography only allows imaging of a small area of the body at a time but allows
visualisation of the internal organ parenchyma. Ultrasonography is a dynamic modality
and is therefore useful for assessment of cardiac movement and blood flow using the
Doppler facility. Ultrasound waves are blocked by gas and therefore the ultrasonography
of the abdomen of small herbivores is greatly hampered by the pockets of gas present.
Artefacts and over-diagnosis are common in ultrasonography. It is vital therefore that the
ultrasonographer is familiar both with the normal anatomy of the species under
examination as well as with the basic practice of ultrasonography. Radiography is a
much more familiar imaging technique to most clinicians and the images once taken can
be read by others. Interpretation of the ultrasound image requires a knowledge of where
the probe was placed on the animal, moving images being more easily interpreted than
still images, making second opinions of ultrasonographic findings difficult.
31
Small Mammal Radiology and Ultrasonography
Text taken from Redrobe S. 2001. Imaging techniques in small mammals. Seminars in
Avian and Exotic Pet Medicine. 10(4):187-197
Radiography
Radiographic technique
The patient must remain motionless for the exposure of the radiograph. Although some
individuals may remain in the desired position, it is often less stressful and easier to
sedate or anaesthetise the small mammal patient with isoflurane or a reversible
injectable regime (See tables 1 and 2). The hair coat should be clean and dry. Water or
dirt on the coat will produce artefacts on the radiograph. Plain films must always be
taken prior to contrast studies in order to provide comparison, assessment of the
exposure factors and to avoid masking a diagnosis.
Exposure settings, film and cassette types must take into account the small size of the
patient. Radiography of the small mammal generally involves patients less than 10cm
thick and less than 10 Kg weight. The radiographic equipment should be capable of
producing 300 mA and obtain a minimum exposure time of 0.008 second. The use of a
higher mAs will allow a lower kVp exposure. The kVp used is usually in the range of 35 60. The higher setting will be used for thick bone or superimposed bone e.g. rabbit skull
radiography. High resolution film screens are essential to obtain diagnostic radiographs
in the smaller patients. High detail, rare- earth intensifying screens with appropriate films
should be used. Mammography film may be used to give enhanced soft tissue detail.
Radiography cassettes and screens designed for human extremities are useful. An
enlarged image can be produced using special techniques. The primary enlarged x-ray
image is produced by a reduction of the focal-film-distance to 80 cm at a given focal size
of 0-15 mm. The advantages of this technique as compared to conventional x-ray
methods are exemplified in a publication with x-ray images from the shoulder joint of a
European hamster and a renovasography of a rat (1).
Positions
Thoracic radiography is used to assess lesions of the heart, lungs, and mediastinum.
Ventro -dorsal and lateral views are standard. Both right and left lateral views are
required to gain maximum information. Radiographic evaluation of the lung fields is
32
enhanced by exposing the radiograph at maximum inspiration, either on natural
inspiration or by positive pressure ventilation of the intubated patient. Ventrodorsal and
lateral views are standard for the abdomen. Abdominal radiography is used to assess
the liver, kidneys, spleen, urogenital tract and gastrointestinal tract. Lateral and
dorsoventral are the standard views for skull radiography. A rostro-caudal view may also
be taken. Both right and left lateral views should be taken in order to assess unilateral
lesions. The dorsoventral view is used to image the tympanic bullae. Oblique views of
the skull may allow greater examination of certain areas, as superimposition over the
area of interest can be reduced. Skull radiography is indicated for assessment of dental,
nasal, sinus, ear or ocular conditions.
Radiography contrast techniques
Urinary tract
The urinary bladder wall and urine are both of soft tissue density therefore
indistinguishable on plain radiography. Likewise soft tissues densities within the urine
e.g. blood clots, tumour, radiolucent calculi, will not be visible. The use of contrast
material allows the assessment of the mucosa, bladder wall thickness and luminal
contents. Negative contrast material involves the replacement of urine with air. Positive
contrast replaces the urine with an increased density media e.g. an iodine-based
solution. Double contrast studies use both techniques in combination to demonstrate for
example, a tumour by negative contrast and the associated blood clots by positive
contrast media.
Stomach
Plain film radiography may be used to demonstrate air in the stomach, radio-opaque
foreign body, abnormal size or position. A negative contrast study involving the use of air
is known as pneumogastrography. Generally 5ml of air per kg body weight are
introduced into the stomach via tube to assess stomach position or visualise extramural;
masses. Positive contrast studies, with medium given at given at 3-10ml per kg
bodyweight are used to investigate stomach position, shape and gastric emptying time.
As rabbits and rodents cannot vomit, care must be taken not to overinflate the stomach
or rupture may result. Contrast studies are performed on an empty stomach where
possible to avoid artefacts or masking lesions by ingesta. The rabbit stomach is never
completely empty therefore ingesta present in the stomach is normal and cannot be
33
eliminated by starvation. Double contrast studies are useful for delineating foreign body
and wall lesions e.g. ulcer, tumour. Subtle lesions are often more apparent when most of
the contrast material has left the stomach. Gastric emptying generally begins
immediately or within 30 minutes and in the monogastric rodents is often complete within
3 hours. However, emptying times are variable between species and individuals and are
affected by a number of sedative and general anaesthesia agents. According to one
study in rabbits (2) 32% of a liquid marker reached the cecum in 1 hour, and 80%
reached it by 12 hours. Liquids were retained for prolonged periods in the cecum. Solid
markers reached the cecum from the stomach in about 4 hours. Some barium will stay in
the stomach for days but some will move through unless there is an obstruction or ileus.
Small intestine
Compete obstructions or radiodense foreign bodies may be detected on plain
radiography. Contrast studies are used to evaluate the position of the small intestine,
partial obstructions and lesions. Approximately 3-12ml of contrast liquid per kg
bodyweight is given orally. Transit times are variable between species and individuals
and are affected by a number of sedative and general anaesthesia agents. The study
ends when all the contrast material reached the large intestine. Radiographs are taken
generally from 5, 15, 30 minutes after administration then hourly thereafter. These times
may vary according to the rate of passage in order to obtain a full series of images
showing progression of the material through the small intestine.
Intravenous urography
Changes in kidney shape and structure and ureters size and position are more readily
identified when contrast material is flowing through them. Intravenous urography
describes the technique where contrast material is dosed at approximately 1ml per kg
bodyweight intravenously. The radiographs must be taken immediately, then at 30
seconds, 1 minute, 2 minutes, 5 minutes intervals obtaining ventrodorsal views of the
caudal abdomen. Lateral views may be taken at 2 and 5 minutes. These times are
variable between individuals and species; radiographs must be taken more quickly in
smaller mammals and less often in larger mammals.
Myelography
34
Myelography is a technique whereby contrast material is introduced into the
subarachnoid space to delineate the spinal cord. This technique allows identification of
narrowing of the spinal canal and also differentiation between extradural, intradural and
intramedullary lesions. Plain lateral and ventrodorsal radiographs are obtained first.
Although in theory the site may be accessed via both the lumbar and cisternal areas, the
relatively larger cisternal site is more practical in small mammals. The technique is
similar to that of the dog, hence the reader is referred to standard texts. Radiography is
needed to confirm the position of the needle if no cerebrospinal fluid (CSF) flows to
indicate penetration of the subarachnoid space. Where possible, some CSF is extracted
then contrast material slowly injected at a maximum of 0.3ml per kg bodyweight.
Radiographs are taken in fully flexed as well as extended positions to fully examine the
spine.
Anatomy relevant to radiography
Gastric trichobezoars are common in rabbits and few animals with these foreign bodies
developed chronic anorexia (3). Therefore such radiographic findings must be
interpreted in the light of clinical signs. The group of hystricomorph rodents includes the
guinea pig and the chinchilla. These species therefore share a common dental formula
(see table 3) and gastrointestinal tract anatomy. Both are hind gut fermenters with large
stomach and caecum. Males posses an os penis. The newborn are precocious i.e. fully
furred with the eyes open. The long jejunum of the chinchilla almost fills the entire
abdominal cavity. Chinchilla litters average 1-2 young although the litter size any range
up to six. The unusual guinea pig dentition warrants comment. The roots of the maxillary
premolars and molars lie laterally whereas the roots of the mandibular cheek teeth
incline medially i.e. the lower cheek teeth appear to fall towards the tongue and the
upper teeth towards the cheeks in the normal animal. The large thin walled caecum of
the guinea pig contains a number of inner divisions and is situated on the left side of the
abdomen. The liver has 6 lobes. The pubic symphysis is fibrocartilagenous in both
sexes. It may ossify in aged males. Litters average 4 to 6 young. Murine rodents include
the rat, mouse, hamster, and gerbil. Litters range from 2-14 or more. The young are
altricial i.e. born hairless with the eyes and ears sealed. Cheek pouches, especially
prominent in the hamster, may store large amounts of food and debris that may be
visible on radiography. In African hedgehogs the first incisor is longer than the others.
Hedgehogs possess a simple stomach and no caecum. Litter size ranges from 1-6 pups
35
that are altricial. Short grooved spines cover the entire dorsum of the body. The face,
legs and ventrum do not possess spines. These spines are visible on radiography.
Common radiographic findings by region
Common radiographic findings are summarised in Table 4.
Skull
Dental disease is perhaps the most common presenting condition in pet rabbits and
rodents. Skull radiography is essential in evaluating for proper diagnosis and evaluation
of dental and associated bone pathology. Dental radiography is also required prior to
tooth extraction especially if infection or involvement of other teeth is suspected (4). The
dorsoventral view is used to visualise any lateral spurs from the cheek teeth (premolars
and molars) and pathology associated with the root of the incisors. The lateral view is
also useful in assessing skull conformation. Mandibular prognathism (relative overlong
lower jaw or maxillary shortening) has long been known to be an inherited condition in
rabbits (5). Mandibular prognathism as well as brachycephalism is now common in UK
pet rabbit dwarf breeds (6). Incisor malocclusion and overgrowth therefore occurs (see
figure 5). Cheek teeth (premolar and molar) elongation may occur in those species that
have continuously growing cheek teeth i.e. rabbit, chinchilla and guinea pig. This may be
due to lack of wear (6) or osteopaenia (7). Lysis of the alveolar bone is an early
radiographic sign (see figure 6). Dystrophic root growth, further lysis and proliferation of
the bone indicate a progression of this disease and the presence of osteomyelitis. Rabbit
bone in particular mounts a very aggressive response to infection, radiographically
similar to osteosarcoma in the dog. Post mortem studies of rabbit skulls revealed bone
of poor quality with deformed teeth having little or no enamel (8). Radiography of these
cases should investigate the following possible sequelae; distorted growth of the roots
penetrating the maxillae, mandibles and orbits, osteomyelitis, abscess formation or
infections of the lacrimal duct or nasal cavity. Intra-oral radiography is limited in small
mammals due to their small oral cavities and opening however a technique for intra-oral
radiography in rodents has been described (9).
Chinchillas presenting with ocular discomfort, e.g. epiphora, should have skull
radiography. This epiphora may be in response to pain from root elongation, tooth root
penetration of the orbit or obstruction of the lacrimal duct (see figure 7). Retrobulbar
abscessation is relatively common in the rabbit and presents as exophthalmos.
Radiography of the skull is required to check for signs of osteomyelitis. Radiography of
36
the thorax is also indicated as some cases of exophthalmos are related to thymoma or
other thoracic masses (10, 11).
Dacryocystitis (infection of the nasolacrimal duct) is a common finding in the rabbit in
clinical practice and should be investigated with radiography. The nasolacrimal duct runs
from the single punctum in the lower eyelid through the bony naso-lacrimal canal in the
maxilla, over the roots of the cheek teeth and down over root of the first incisor. The
nasolacrimal ducts empties into the nose at a position rostro-medial to the apex of the
incisor root. Therefore pathology of these structures will impinge on the duct and
promote blockage and infection. The nasolacrimal duct may be cannulated and radioopaque contrast material instilled into the duct to allow investigation of abnormalities.
Marked unilateral dilatation of the duct proximal to a dorsal flexure at the caudal limit of
the incisor tooth root has been reported (12). Occlusion of the nasolacrimal duct has
been attributed to fat droplets (12), scar formation or blockage with purulent or
inflammatory debris.
Facial masses should be investigated using radiography. The differential diagnoses
include bacterial or fungal infection of soft tissues or bone, trauma, bone cysts or
neoplasia. An osteogenic sarcoma has been reported affecting the mandible of a rabbit
(13).
Sclerosis of the tympanic bullae is a frequent finding in pet rabbits and to a lesser extent
guinea pigs, chinchillas and rats. This is because (sub) clinical otitis media is common in
these species. As this radiographic finding can occur in the absence of clinical sign it is
difficult to interpret this finding in conjunction with torticollis. Radiology and otoscopy
were tested as means of antemortem screening for affected guinea pigs (14). Radiology
gave 96% accuracy in diagnosing otitis media and proved to be a more satisfactory
technique than otoscopy.
Skeletal structures
Osteoarthritis is noted to occur in many small mammals, including guinea pigs.
Radiographic changes include marginal osteophytes of the tibia and femur, sclerosis of
the subchondral bone of the tibial plateau, femoral condyle cysts, and calcification of the
collateral ligaments in guinea pigs (15). Such changes may also occur in association
with vitamin C deficiency in guinea pigs. A spontaneously occurring disorder of joints
known as progressive ankylosis has been reported in mice (16). Clinically, peripheral
joints are inflamed initially, then became ankylosed. Axial joint involvement produced
37
severe spinal ankylosis. Extraarticular manifestations included balanitis and crusting skin
lesions. Radiographically, bony erosions and calcification of articular and periarticular
tissues are extensive, with vertebral syndesmophytes. Studies of the radiographic signs
of skeletal maturity in rodents show that no fusion is apparent up to 134 weeks in certain
epiphyses of the rat (17). The rat reaches bone maturity at 17 to 21 weeks of age and
the mouse 17 weeks.
Spontaneous degenerative changes of the spine have been
described in the rabbit (18). Three types of lesion were observed. The nucleus pulposus
underwent chondroid metaplasia throughout the length of the vertebral column by the
age of 2 years. Hydroxyapatite deposition was found in the nucleus pulposus in 12 of 20
animals examined radiographically. The lesion occurred principally in the distal thoracic
segments and was first observed in 3-month-old rabbits. Spondylosis occurred in spines
from animals greater than 24 months old. Portions of the spine spared by disc
calcification were affected.
Ulcerative pododermatitis occurs in rats, guinea pigs and rabbits more than other pet
species. It must be investigated using radiography, as many chronic or severe lesions are
associated with osteomyelitis. Predisposing factors must be addressed. In guinea pigs, a
vitamin C deficiency should be suspected. Guinea pigs lack the enzyme L gulonolactone
oxidase and so need pre-formed vitamin C in their diet. Vitamin C is required to form
collagen that is required for joints, skin (including wound healing) and ligaments
(including those that anchor the teeth). In vitamin C deficiency there may be swelling of
the joints of the limbs and along the ribs at the costochondral junctions, with fractures,
osteoporosis and bleeding into joints.
Hedgehogs feed predominately on insects and small vertebrates. In captivity, an
unsupplemented insect diet leads to nutritional hyperparathyroidism and metabolic bone
disease. Radiography in these cases will reveal a thinning cortical bone, lack of
trabecular pattern in the long bones, generalised loss of bone density, folding fractures
and collapsing spine.
Thoracic radiography
Neurofibrosarcoma of the limbs in the rabbit have been associated with thymomas (19).
It is therefore wise to perform thoracic survey radiography, including the cranial portion
of the mediastinum, in cases of such neoplasia in rabbits. Hypertrophic osteopathy has
been associated with an intrathoracic neoplasm in a rabbit (20). Thoracic radiography as
well as radiography of the skull and orbit may also prove useful in cases of
38
exophthalmos, as such clinical signs have been associated with mediastinal thymoma
(10, 11). Extensive mineralization of the brachiocephalic trunk, and the left subclavian,
both iliac, common carotid arteries has been detected in the rabbit using radiography
associated with atherosclerosis (21). Pulmonary metastases may arise from uterine
adenocarcinoma in the rabbit therefore thoracic as well as abdominal radiography is
indicated in these cases. (22). Radiography can be used to check for thoracic
metastases from skin tumours e.g. Squamous cell carcinoma of the midventral
abdominal pad in gerbils (23) and mammary tumours. The cardiac silhouette of the
normal ferret is elevated from the sternum on the lateral view by fat in the ligament from
the heart to the sternum and so this radiographic finding should not be misinterpreted as
a pneumothorax (24). Normal ferrets should have only a small amount of gas in the
gastrointestinal tract and the spleen is often large (25). Dilated cardiomyopathy is the
most common cardiac abnormality in ferrets (26). Radiography will reveal an enlarged
cardiac silhouette, pleural effusion, pulmonary edema, ascites and hepatosplenomegaly.
Confirmation is by ultrasonography. Megaesophagus has been reported in the ferret and
may be diagnosed on history, clinical signs and the radiographic findings of dilated
esophagus, aerophagia or aspiration pneumonia (27).
Abdominal radiography
The large caecum of the rabbit, chinchilla and guinea pig dominates radiography of the
abdomen whereas in the monogastric rodents i.e. rat, mouse, gerbil, hamster, the
abdominal anatomy and proportions are similar to the dog and cat. Calcification of the
abdominal aorta and iliac vessels has been reported in rabbits associated with
atherosclerosis (21). Hepatomegaly may be associated with hepatic coccidiosis (4). The
detection of ileus e.g. excessive gas in the small intestine, no movement of
ingesta/contrast in sequential radiographs that are indicative of a gastrointestinal tract
problem in rabbits, not merely the radiographic finding of a mass in the stomach (3).
Lead poisoning caused by the ingestion of lead objects may be diagnosed by the finding
of a metallic object in the gastrointestinal tract by radiography and elevated blood lead
levels (28.). Delayed gastric emptying, as detected using barium sulfate contrast
radiography in the ferret, had been reported in a case of granulomatous enteritis (29).
Gastric foreign bodies in the ferret may be indicated by segmental ileus, gaseous
distention of the stomach with occasionally finding the foreign body radiographically (27).
The unique calcium metabolism of rabbits results in calcium excretion in relatively large
39
amounts via the kidneys. These calcium salts are often visible radiographically in the
bladder and may not be associated with clinical signs. Discrete uroliths may also form
and are usually calcium carbonate (30). Guinea pig, chinchilla and rat possess an os
penis that may be confused for a urolith if the anatomy is not known. Imaging of the
kidneys, ureters and bladder may be enhanced using contrast techniques. Such a
technique has been described, albeit experimentally, in the rat (31). Radiography may be
used to detect pregnancy and evaluate dystocia. Mummified fetus associated with
uterine rupture has been reported in the rabbit; radiography was used to diagnose the
condition. (32).
Ultrasonography
The ultrasonographer is faced with a number of difficulties when approaching
ultrasonography of exotic species. There are few reference data regarding the normal
and abnormal ultrasonographic anatomy of these species even though the application of
ultrasonography to exotic species was first suggested in 1978 (33). There are relatively
few individuals who are familiar with both ultrasonography and the veterinary aspects of
exotic species. For the common small exotic pet species, perhaps a minimum
requirement is high definition transducers with a footprint of less than 2cm. As ‘exotic
species’ may include individuals ranging from a 20g mouse to a 10kg rabbit, a full
complement of linear, sector, curvilinear probes from 3.5 to 20 MHz will be required for
the exotic species enthusiast. Functions other than 2D real time imaging, e.g. Colour
Doppler, Power Doppler, Pulse wave, M mode capabilities, are required to image blood
flow and perform echocardiography. Acoustic coupling gel is applied liberally to the skin
and transducer. In some species e.g. chinchilla, ultrasonography is possible through the
fur if sufficient gel is used to exclude air however some hair removal is required in most
species. This should be minimised as large areas of hair loss can predispose the animal
to hypothermia. Care should be taken not to excessively wet or chill the small mammal,
as hypothermia, especially during sedation or general anaesthesia, can be fatal. In
general, the anatomy of the small mammals is similar to the more familiar domestic
species, therefore positioning of the animal and transducer placement are similar. In all
but the most tractable individuals, it is often preferable to sedate or perform general
anaesthesia. Short acting or reversible agents are preferred (see tables 1 and 2).
Normal and abnormal ultrasonographic anatomy
40
Conditions where ultrasonography may prove useful in exotic mammalian medicine are
described in table 5. Ultrasonography of the abdominal organs may be hindered by the
presence of a large hindgut found in rabbits, chinchillas and guinea pigs.
Ultrasonography of the bladder, uterus, liver (see figure 8) and spleen is possible
percutaneously via the ventral abdomen in most species. Ultrasonography of the kidneys
(see figure 9) and ovaries is easier percutaneously via the flank. Rabbits and rodents
possess an open inguinal canal therefore the testes may ascend into the abdomen when
palpated.
Echocardiography
The heart rates of small mammals are much faster than the human (for which most
machines are designed) or the dog. The rabbit heart rate varies between 150-250 beat
per minute whereas the mouse may have a rate of over 250. The ultrasound machine
must have a frame rate or update rate fast enough to image these ‘fast hearts’ or the
cardiac image will merely be a blur. Echocardiography has been described in the rabbit
(34, 35, 36) and in the mouse (37) and in the rat (38). The following measurements
could be the most useful and accurate in small mammals: 1) left ventricular systolic time
intervals; 2) right ventricular systolic time intervals; 3) right ventricular end-diastolic
dimension; 4) left atrial internal dimension; 5) left ventricular end-diastolic and endsystolic dimensions; 6) systolic slope of the interventricular septum; 7) mid-diastolic
partial closure of the mitral valve (EF slope); and 8) systolic slope of the posterior aortic
wall (see table 6). The ultrasonographer should note the sedative or anaesthetic drugs
used to restrain the animal as many of these affect myocardial contractility and other
factors. For example, myocardial contractility in rabbits is higher under isoflurane/nitrous
oxide anaesthesia than halothane/nitrous oxide anaesthesia (35). In addition,
ultrasonography has been used to evaluate heart damage caused by general
anaesthesia agents e.g. myocardial fibrosis has been associated with ketamine/xylazine
anesthesia in rabbits and detected using ultrasonography (36). Cardiomyopathy is a
relatively common post mortem finding in aged rabbits. As pet rabbits longevity
increases, the incidence of heart failure and atherosclerosis has been increasing (39).
Dilated cardiomyopathy is the most common cardiac abnormality in ferrets (26).
Confirmation is by demonstrating a reduced fractional shortening on ultrasonography.
Echocardiography is recommend in rabbits exhibiting exercise intolerance or dyspnoea.
The author has detected a ventricular septal defect in a rabbit presenting with chronic
41
dyspnoea. It is likely that as this technique becomes more widely used in the small
mammal patient, more conditions will be identified in vivo.
Other organ ultrasonography
Ultrasonography has been used to detect ureterolithiasis in a guinea pig (40) and in the
investigation of renal disease has been described in the rat (41). Urethral obstruction in
the male ferret may be due a hypertrophied prostate in response to adrenal disease.
Abdominal ultrasonography will reveal adrenomegaly in those cases (27).
Contrast
media may be used to evaluate renal pathology. Iohexol has been reported to be less
nephrotoxic than other, higher osmolarity, contrast agents (42). Ultrasonography may be
used to perform an ultrasound-guided biopsy of the kidney in order to perform histology
and reach a definitive diagnosis.
Contrast agents may be used to enhance the visualisation of hepatic and splenic
masses and has been reported as successful in the rabbit (43). Hepatic lipidosis is an
important sequel to anorexia and is relatively common in anorexic rabbits, chinchillas,
guinea pigs and ferrets. Ultrasonography may be used to examine the liver; an
increased echogenicity is compatible with hepatic lipidosis. An ultrasound-guided biopsy
may be performed to allow histological investigation of liver disease.
Diagnosis of pregnancy and disease by ultrasound in exotic species has been reported
over 10 years ago (44). The use of uultrasonography in pregnancy diagnosis specifically
in the rabbit has been reported (45, 46). Ovarian cysts have been reported in guinea
pigs and detected using ultrasonography
(47). Clinical signs included anorexia,
alopecia, or depression. Ultrasonographic features of the 2- to 3-cm diameter fluid-filled
cysts included compartmentalization and connection to the ovary. Ultrasonographic
detection of adrenal gland tumor and ureterolithiasis has been reported in the guinea pig
(40). Although splenomegaly may be a ‘normal’ finding in ferrets, abnormalities in the
splenic parenchyma detected by ultrasonography indicate pathology (27). Uterine
adenocarcinoma and pyometra may be diagnosed and differentiated by ultrasonography
in the rabbit (28).
More advanced imaging
Computerised tomography (CT) scanning
CT scanning uses x-rays and computer calculations to produce an image of a ‘slice’ of
the patient. The differentiation between soft tissue and fluid is easiest with CT than
42
conventional radiography. CT allows imaging of an area without superimposition of
adjacent structures. The radiation dose to the patient is higher than with conventional
radiography. The modality is expensive to use. It is therefore often restricted to the
investigation of intracranial lesions, nasal cavity, sinus, orbit, middle ear, metastases
within organs, that neither radiography nor ultrasonography can image well. CT is ideal
for bone and calcium imaging. Meniscal ossification in spontaneous osteoarthritis in the
guinea pig has been demonstrated using CT scanning (48). CT scanning was used to
investigate tooth structure in chinchillas (Chinchilla laniger), both cheek tooth crown and
root abnormalities being common in this species (49). Early pathological changes were
identified which are not detected by radiography (49). CT is useful in the assessment of
bacterial sinusitis in rabbits, as true anatomic cross sections of the sinuses are achieved
(50)
Magnetic Resonance Imaging (MRI)
Rather than use radiation, MRI uses computer generation of pictures measuring the
hydrogen content of tissues. The spacial resolution and soft tissue contrast is higher with
this technique than with CT. The images can be viewed in any plane. MRI is very
sensitive to any movement, which will blur the image. Therefore the patient must be
under deep sedation or general anaesthesia. Even gastrointestinal tract peristalsis can
blur the image. MRI is excellent for musculoskeletal and articular imaging and also for
brain lesions. To date most reports of the use of MRI in small mammals are from the
experimental literature and include imaging such lesions as; pyelonephritis in rabbits
(51), spinal abscesses in rabbits (52), synovitis in rabbit (53), bacterial sinusitis in rabbits
(50).
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Anim Sci Feb;30(1):60-3, 1980
32 Harper PA, Ensley PK. Mummified fetus associated with uterine rupture in a New
Zealand white rabbit (Oryctolagus cuniculus). Lab Anim Sci Oct;32(5):518-9, 1982
33 O’Grady JP, Yeager CH, Thomas W. Practical applications of real time ultrasound
scanning to problems of zoo veterinary medicine. J Zoo Anim Med 9:52-56, 1978
34 Tello de Meneses R, Mesa MD, Gonzalez V. Echocardiographic assessment of
cardiac function in the rabbit: a preliminary study. Ann Rech Vet;20(2):175-85, 1989
35 Marano G, Formigari R, Grigioni M, et al. Effects of isoflurane versus halothane on
myocardial contractility in rabbits: assessment with transthoracic two-dimensional
echocardiography. Lab Anim Apr;31(2):144-50, 1997
36 Marini RP, Li X, Harpster NK, Dangler C. Cardiovascular pathology possibly
associated with ketamine/xylazine anesthesia in Dutch belted rabbits. Lab Anim Sci
Apr;49(2):153-60, 1999
37 Manning WJ, Wei JY, Katz SE, Douglas PS, et al. Echocardiographically detected
myocardial infarction in the mouse. Lab Anim Sci Dec;43(6):583-5, 1993
38 Nakamura T, Shimoo K, Kuribayashi T, et al. Visualization of the heart and
determination of left ventricular mass in rats by echocardiography. Jpn Heart J
Jul;32(4):481-91, 1991
39 Deeb BJ, DiGiacomo RF. Respiratory diseases of rabbits. Vet Clin North Am Exotic
Anim Pract; 3:465-480, 2000
40 Gaschen L, Ketz C, Lang J, et al. Ultrasonographic detection of adrenal gland tumor
and ureterolithiasis in a guinea pig. Vet Radiol Ultrasound Jan-Feb;39(1):43-6, 1998
41 Suzuki K, Hashimoto S, Imamichi T, et al. Differential diagnosis of hydronephrosis
types I and II in rats by echography. Nippon Juigaku Zasshi Jun;49(3):543-6, 1987
42 Duan SB, Liu FY, Luo JA, et al. Nephrotoxicity of high- and low-osmolar contrast
media. The protective role of amlodipine in a rat model. Acta Radiol Sep;41(5):503-7,
2000
43 Forsberg F, Goldberg BB, Liu JB, et al. Tissue-specific US contrast agent for
evaluation of hepatic and splenic parenchyma. Radiology Jan;210(1):125- 32, 1999
44 Du Boulay GH, Wilson OL. Diagnosis of pregnancy and disease by ultrasound in
exotic species. Symp.Zool.Soc.Lond 60:135-150, 1988
45 Inaba T, Mori J, Torii R Use of echography in rabbits for pregnancy diagnosis Nippon
Juigaku Zasshi Oct;48(5):1003-6, 1986
46 Cubberley DA, Lee TG, Laughlin CL, et al. Importance of ultrasound determination of
pregnancy in the rabbit. Am J Vet Res;43(10):1802-3, 1982
47. Beregi A, Zorn S, Felkai F. Ultrasonic diagnosis of ovarian cysts in ten guinea pigs.
Vet Radiol Ultrasound Jan-Feb;40(1):74-6, 1999
48 Kapadia RD, Badger AM, Levin JM, et al. Meniscal ossification in spontaneous
osteoarthritis in the guinea pig. Osteoarthritis Cartilage Sep;8(5):374-7, 2000
49 Crossley DA, Jackson A, Yates J, et al. Use of computed tomography to investigate
cheek tooth abnormalities in chinchillas. J Small Anim Pract Aug;39(8):385-9, 1998
50 Kershner JE, Cruz MJ, Betse DJ et al. Computed tomography versus magnetic
resonance imaging of acute bacterial sinusitis in a rabbit model. Am J Otolaryngology;
21(5):298-305, 2000
51 Runge VM, Timoney JF, Williams NM. Magnetic resonance imaging of experimental
pyelonephritis in rabbits. Invest Radiol. 32(11):696-701, 1997
45
52 Runge VM, Williams NM, Lee C, et al. MRI imaging in a spinal abscess model.
Preliminary report. Invest Radiol. 33(4):246-55, 1998
53 Strouse PJ, Londy F, DiPetro MA, et al. MRI evaluation of infectious and no infectious
synovitis: preliminary studies in a rabbit model. Pediatr Radiol. 29(5):367-7, 1999
54 Orcutt C. Cardiac and respiratory disease in rabbits. 2000 Proc of British Veterinary
Zoological Society, Autumn meeting, 2000, Pp68-73
Table 1. Injectable agents for sedation and general anaesthesia in mammals
drug
mouse
rat
Guine
a pig
Hypnorm
0.2- 0.5 ml
as mouse
0.5 (fentanyl/
i/m 0.3-0.6 i/p
1.0
fluanisone)
ml/kg
i/m
Hypnorm(fentanyl 0.4ml/kg / 5
ml/kg
1 ml/kg
/ fluanisone)/
i/p
2.5 i/p
2.5
diazepam
i/m
Hypnorm &
10 ml/kg* i/p
2.7 ml/kg*
8
midazolam*
i/p
ml/kg*
i/p
ketamine/
200 / 0.5 i/p
90/ 0.5 i/p
40 i/m
medetomidine
0.5 i/m
propofol
26 i/v
10 i/v
*One part Hypnorm, one part midazolam, two parts water
rabbit
0.2- 0.4 ml
i/m
Duration of
anaesthesia
sedation only 30-45
minutes
0.3ml/kg i/m
2 i/p
45-60 mins
ml/kg i/m
0.5-1 i/v
45-60 mins
35 i/m 0.5
i/m
10 i/v
20-30
5 minutes
Table 2. Reversal agents for sedative/general anaesthesia agents
agent
To reverse
Dose mg/kg
atipamazole any combination using
1
medetomidine
buprenorphi any combination using Hypnorm
0.05 rabbit; -0.1 small
ne
rodents
butorphanol any combination using Hypnorm
0.3 rabbit 1 small rodents
46
route
i/m i/p s/c
i/v
i/m i/p s/c
i/v
i/m i/p s/c
i/v
Table3. Dentition of common small mammal pet species
Species
Dental formula
Incisor, canine, premolar,
molar
rabbit
2/1, 0/0/, 3/2, 2/3
Hystricomorph rodent ( guinea pig,
1/1, 0/0, 1/1, 3/3
chinchilla)
African hedgehog
3/2, 1/1, 3/2, 3/3
murine rodents (rat, mouse, gerbil,
1/1, 0/0, 0/0, 3/3
hamster)
Total number of
teeth
26
20
36
16
Table 4. Conditions for which radiography is a useful diagnostic tool in small
mammals
Species (noting most
common species
affected)
Rabbit, guinea pig
rabbit
rabbit
chinchilla
rabbit
rabbit
rabbit
Rabbit, Hystricomorph
rodent
rabbit
Guinea pig
Guinea pig
Guinea pig
Guinea pig
rabbit
rabbit
rabbit
Rabbit, rodents
Rabbit, rat, guinea pig
Rabbit, all
all
rabbit
all
Rabbit, guinea pig, all
all
Guinea pig
all
Guinea pig
Chinchilla, guinea pig, all
Hedgehog, all
Hedgehog, all
Lesion
urolithiasis
(pre) molar root elongation
Osteomyelitis
Premolar root penetration of orbit
Incisor elongation
(pre)molar malocclusion
Fracture L7
Ileus, gas filled small intestine
Uterine adenocarcinoma
Uterine teratoma
Cystic ovaries
Leukaemia, lymphosarcoma
Streptococcus zooepidemicus abscessation
Caecal impaction
Trichobezoars
Rhinitis
Inner ear infection, otitis
Pododermatitis
Spondylosis of the spine
Pneumonia
Rectal papillomata
Retrobulbar abscess, osteomyelitis
Pulmonary metastases e.g. from uterine carcinoma
(rabbit), mammary tumours (guinea pig)
Lead poisoning
Os penis
arthritis
Vitamin C deficiency
intussusception
Neoplasia of gastrointestinal tract
Nutritional hyperparathyroidism, metabolic bone
47
disease
48
Table 5. Conditions for which ultrasonography is a useful diagnostic tool in small
mammals
Problem
Species
Possible causes
Ultrasonography
renal
all
Infection
Examination of organ
disease,
Degeneration
Ultrasound guided biopsy
liver
Toxicity
for histological
disease
neoplasia
examination
pregnancy
guinea pigs, rabbit
Large foetus
Determination of
toxaemia
Dead foetus
pregnancy
obesity
Determine whether
foetus alive or dead
Diarrhoea
all
dietary change, stress, enteritis Identify intussusception,
(bacterial, fungal, viral)
foreign body
Diarrhoea
rabbit
coccidiosis
vomition
ferret
Respiratory
disease
Myiasis (fly
strike)
all
Ingestion of foreign body
Gastritis
Lymphoma
Gastric neoplasia
Viral, bacterial, fungal infection
Cardiac disease
Carnivorous maggots
Haematuria
all
Lameness,
lethargy,
weakness
ferret
subcutaneo
us masses
rabbit, rodents,
ferret
Ovarian
enlargemen
t
Uterine
enlargemen
t
All (guinea pig)
All (rabbit)
all
urolithiasis
cystitis
neoplasia bladder
neoplasia uterus
renal infection
normal red pigments
insulinoma
lymphoma
adrenal gland disease
anaemia (persistent estrous)
Aleutian disease
canine distemper
cardiomyopathy
abscess
sebaceous adenoma (guinea
pigs)
neoplasia
lipoma
Cystic ovaries
Pyometra
Uterine adenocarcinoma
(rabbit)
49
Hepatobiliary tree dilation
associated with hepatic
coccidiosis
Detection of foreign body,
gastric wall abnormality
Investigation of cardiac
disease
detection of maggots
within the abdominal
cavity
Investigation of
urogenital tract
Examination of pancreas,
lymph nodes, adrenal
glands, heart
Facial abscesses in
rabbit are often related to
dental infection or
osteomyelitis
Fluid filled cysts attached
to ovary
Ultrasonography of
uterus to differentiate
lesions
Subcutaneo
us,
abdominal
masses
ocular
protrusion
guinea pig
rabbit
Uterine haemorrhage/ ruptured
venous aneurysm
cervical adenitis, abdominal
lymph node abscessation
caused by Streptococcus
zooepidemicus
Abscess or neoplasia
retrobulbar
50
Examination of
abdominal lymph nodes
Examination of
retrobulbar area to
differentiate
Table 6. Echocardiographic parameters in rabbits under diazepam sedation. (From
36, 54)
Parameter
Left ventricular end diastolic dimension (LVEDD)
Left ventricular end systolic dimension (LVESD)
Shortening fraction (%D)
Left ventricular ejection time (LVET)
Velocity of circumferential fibre shortening (VCF)
Ejection fraction (Ej fract)
Left ventricular free wall thickness diastolic (LVFW Th d)
Interventricular septum thickness diastolic (IVS Th d)
Left atrial dimension systolic (LADs)
Left atrial to aortic root ratio (LA/ Ao)
Right atrial dimension systolic (RAD s)
Right atrial to aorta ratio (RA/Ao)
E point septal separation (EPSS)
DE excursion (DE excurs)
E to F slop (EF slope)
Right ventricular outflow velocity (RVOT vel)
Left ventricular outflow velocity (LVOT vel)
51
Value
1.17 +/- 0.19
0.7 +/- 0.09
39.5 +/- 5.39
0.08 +/- 0.01
4.74 +/-0.45
76.17 +/- 5.81
0.31 +/- 0.08
0.25 +/-0.05
0.17 +/-0.41
1.38 +/- 0.32
0.61 +/- 0.08
0.88 +/- 0.17
0.05 +/- 0.05
0.55 +/- 0.08
70.17 +/- 31.82
0.83 +/- 0.10
0.65 +/- 0.14
Imaging techniques in pet birds
Sharon Redrobe BSc (Hons) BVetMed CertLAS DZooMed MRCVS
RCVS Diplomate in Zoo and Wildlife Medicine
RCVS Recognised Specialist in Zoo and Wildlife Medicine
[email protected]
Ultrasonography and radiography are complementary imaging techniques. In rare cases
one technique is used instead of another but more commonly both modalities are used
to maximise diagnostic information.
Ultrasonography is an excellent modality for differentiating between fluid and soft
tissues and is therefore the diagnostic test of choice to investigate lesions of the bladder,
heart and uterus. Radiography requires contrast material to fully explore these organs.
Radiography is useful in determining the size, shape and position of organs within the
body and relative to each other as large areas of the body can be imaged.
Ultrasonography only allows imaging of a small area of the body at a time but allows
visualisation of the internal organ parenchyma. Ultrasonography is a dynamic modality
and is therefore useful for assessment of cardiac movement and blood flow using the
Doppler facility. Ultrasound waves are blocked by gas and therefore the ultrasonography
of the abdomen of small herbivores is greatly hampered by the pockets of gas present.
Artefacts and over-diagnosis are common in ultrasonography. It is vital therefore that the
ultrasonographer is familiar both with the normal anatomy of the species under
examination as well as with the basic practice of ultrasonography. Radiography is a
much more familiar imaging technique to most clinicians and the images once taken can
be read by others. Interpretation of the ultrasound image requires a knowledge of where
the probe was placed on the animal, moving images being more easily interpreted than
still images, making second opinions of ultrasonographic findings difficult.
Avian Radiography
ventro-dorsal restrain bird in crucifix position using micropore tape
lateral
lateral recumbency, legs held back, bird parallel to film
52
Assess skeletal density, lesions (fractures), heart normal lies at the second rib to the fifth
rib.
The lateral margins of the normal heart and liver in psittacine birds create an
hourglass shape (there may be a kink between the two in macaws). On the VD view, the
heart covers much of the lungfield, the abdominal air sacs outline the liver.
Heart size at base should equal about 50% of the width of the coelomic cavity at the
level of the fifth thoracic vertebra. Cardiomegaly is rare and associated with; endocarditis
(often secondary to pododermatitis), chronic anaemia most commonly. Pericardial
effusion shown as a large rounded heart is caused by e.g. Chlamydophilosis, polyoma
virus, TB and neoplasia. Microcardia suggests hypovolaemia and an emergency.
Atherosclerosis is common in older birds maintained on a high fat diet (oily seeds).
On a good quality radiograph, the parabronchi can be seen as a honeycomb pattern to
the lungs. Pneumonic changes are best appreciated at the caudal edge of the lungs on
the VD view. The air sac walls are not readily visible unless they are inflamed when fine
lines may be seen on the lateral view and dorsal views where two membranes are
confluent e.g. the confluent membranes of the caudal thoracic air sac and right
abdominal air sac.
The crop is on the right side of the distal neck but may appear to extend across the
neck, depending upon species and contents.
The liver should not extend beyond the sternum on the lateral view. An enlarged liver is
detected by the loss of the ‘waist’ of the hourglass shape formed with the heart, the loss
of abdominal air sac, the presence of liver lobes beyond the scapula/ coracoid line, a
cranially displaced heart and dorsal elevation of the proventriculus.
The spleen is a rounded object slightly right of midline at the junction of the ventriculus
and proventriculus on the VD view. The gastrointestinal tract is best appreciated
radiographically by the use of barium contrast material. Gas is considered abnormal in
the avian GIT.
The kidneys are normally made visible by the presence of air around them. The cranial
and caudal divisions are best appreciated on the lateral view ventral to the synsacrum.
Masses of the spleen, testis, ovary, intestine may appear as renal enlargement.
The active ovary appears as a bunch of grapes cranial to the kidneys. The active testis
is large and can be misinterpreted as renal enlargement.
53
Avian ultrasonography
The air sacs within the coelom (body cavity) of birds severely restrict the use of
ultrasonography in these animals. Ultrasonography is therefore most useful in the
investigation of the swollen coelom and the differentiation between fluid, soft tissue mass
and organomegaly.
Procedure
Tame parrots, trained raptors and other tractable individuals may be examined under
physical or minimal restraint. In most cases, it is less stressful to the bird and operator if
the bird is lightly anaesthetised using isoflurane (see table 6). Feathers will interfere with
the transmission of the ultrasound beam and require removal over the area of interest. A
minimal area of feathers should be removed as in most species feathers are replaced
only once or twice per year. Feathers should be plucked rather than cut as plucking may
encourage earlier regrowth. In some species, a featherless tract occurs over the caudal
coelom and no plucking is required. Gel is applied to the skin in the normal manner. An
ultrasonography machine with a 7.5-10MHz probe with a foot print of less than 2cm is
required to perform ultrasonography on most pet parrot, pigeon and raptors species. In
most pet birds, weighing 50g to 2kg, the heart rate will be above 150 beat per minute.
The heart itself will measure between 0.5 and 2cm. The ultrasonography equipment
must therefore possess sufficient image definition and update rate to image the heart
effectively.
Transcloacal and transintestinal ultrasonography using high resolution miniaturised
probes have been developed in order to circumvent the problems associated with
transcoelomic
ultrasonography
in
birds.
Transintestinal
ultrasonography
allows
visualisation of the gonads and genital tract whereas transcloacal ultrasonography is
limited to the caudal genital tract.
Normal ultrasonographic anatomy
Note that birds do not possess a urinary bladder. The gall bladder is absent in some
species e.g. pigeon.
54
In the normal bird, scanning percutaneously over the coelomic wall aiming cranially may
contact the liver and allow examination of this organ. Ultrasonography of the liver is
facilitated by hepatomegaly. Similarly, the ovaries are not readily imaged unless follicles,
abscess, granuloma enlarge the organ or coelomic fluid is present. The bursa of
Fabricius may be identified in juvenile birds.
Birds do not possess a diaphragm therefore the apex of the heart contact the cranial
edge of the liver directly. The heart may therefore be imaged ultrasonography by
directing the beam through the liver caudad to craniad.
Abnormal ultrasonographic anatomy
Coelomic ultrasonography is enhanced when coelomic fluid is present as this fluid
displaces the air filled air sacs within the coelom. Care should be taken when examining
such patients, as they will therefore have a degree of respiratory embarrassment.
Laminated and thin-shelled eggs can be differentiated from abdominal masses,
salpingitis and cystic degeneration using ultrasonography.
Hepatomegaly is a relatively common clinical sign in diseased birds. Ultrasonography
may be used to detect masses within the liver parenchyma such as multiple discrete
abscesses associated with Yersiniosis, or biliary tree neoplasia seen in Amazon parrots.
The surrounding air filled air sacs often obscures ultrasonographic imaging of the
normal, quiescent ovary. Enlargement of the ovary caused by normal folliculogenesis, or
abnormal neoplasia or granuloma often facilitates imaging using ultrasonography.
55
Therapeutics: pet birds, small mammals
Sharon Redrobe BSc(Hons) BVetMed CertLAS DZooMed MRCVS
RCVS Diplomate in Zoo and Wildlife Medicine (Mammalian)
RCVS Specialist in Zoo and Wildlife Medicine
Birds
Respiratory Disease
•
signs
acute/chronic dyspnoea, tail-bobbing, increased abdominal effort, open
mouth breathing, respiratory noise (unaided and with stethoscope), voice change,
anorexia, decreased activity, decreased perching, fluffed up appearance
•
diagnostic workup;
blood sample - CBC and biochemistry, Aspergillus ELISA
faecal examination - gram stain, wet prep, PCR/ serology for Chlamydia
transillumination of neck
tracheal / lung wash - Gram’s stain, culture and sensitivity
radiography
endoscopy of upper respiratory tract, laparoscopy of air sac and
abdominal organs (biopsy liver - Chlamydia)
Acute Dyspnoea
•
often due to inhalation of seed by large psittacines or raptor, may be due to
Aspergillus granuloma in the upper respiratory tract
•
EMERGENCY - provide an airway. The abdominal airsac may be cannulated and the
tube sutured in place. Oxygen may be administered via this tube. Once the animal is
stabilised, inhalational anaesthetic may be supplied by this route.
Upper Respiratory Tract Diseases
Includes nares, sinuses.
signs
nasal discharge (stenotic breathing with bilateral caseous; moist respiratory
sounds and sneezing if serous); conjunctivitis, abscesses in pharyngeal areas, impaired
56
flight in more severe cases. Upper respiratory disease is often due to bacterial, fungal,
Chlamydia, viral or trauma factors.
sinusitis
due to bacteria or mycoplasmas (differential diagnoses; Chlamydia, aspergillosis,
candidiasis)
Dxswelling of sinuses, unilateral or bilateral. Radiography, transillumination, C+S of
nasal flush
Tx based on sensitivity, flush out sinuses, infuse AB. Vitamin A therapy. Improve
ventilation and correct temperature/humidity of environment. Doxycycline, enrofloxacin,
tylosin are good first line choices. Or, 25mg oxytetracycline + 25mg tylosin / Kg i/m BID,
or tylan 50 diluted 1:10 in saline and injected into infected sinus
rhinoliths
dust, dirt and nasal mucus blocking external nares, sequel of chronic sinusitis/
hypovitaminosis A
Tx remove with needle point, treat underlying cause
abscesses
lingual, palatine, periocular, submandibular sites. Abscesses of submandibular salivary
gland common in birds fed seeds only.
Tx surgical remove of encapsulated abscess, suture wound. Treat underlying cause
(bacterial infection , hypovitaminosis A)
Lower Respiratory Tract Disease
•
lungs, air sacs, syrinx, trachea
•
signs open-mouthed breathing, gasping, exaggerated thoracic movements, tailbobbing. If cyanotic, feet and beak appear blue (severe cases), wheezing gasping.
air sacculitis
bacterial or chlamydial aetiology most common. Also aspergillosis.
57
Dxradiography, culture, serology, faecal tests to differentiate cause. Laparoscopic
examination of the air sacs following radiographic localisation enables visualisation of
lesion plus direct culturing.
Wheezing and other audible lung sounds have a number of causes;
a) foreign body in trachea
b) parasitic obstruction and inflammation of trachea. Due to organism or exudate
produced.
Syngamus trachea (the tracheal mite), Sternostoma tracheacolum, and the rare air sac
mite Cytodites nudus. Aspergillus colonies can also produce this sound (see antimycotic
drug table)
Dxfaecal examination for oocysts, culture of exudate. Direct examination with
endoscopy.
Clicking/ crying sound;
a) thyroid hyperplasia primarily affects the budgerigar fed cheap loose seed. Iodine
deficiency increases TSH levels causing thyroid hyperplasia and dysplasia. The
enlarged thyroid presses on trachea (producing clicking noise) and bird typically sits
with head pointed forwards to aid ventilation. Pressure on the lower oesophagus can
result in crop dilatation and stasis - weight loss may be a presenting sign therefore. In
severe cases, cardiac embarrassment may result in convulsions and/or partial paralysis.
Dxsigns, dietary history, response to treatment
Tx iodine to drinking water ( 1 part Lugols iodine to 14 parts water; 1 drop to 30mls
drinking water daily for 3 weeks). Provision of a diet supplemented with iodine (Trill;
Pedigree)
b) asthma seen in psittacine and passerine birds, rarely reported.
Other treatment for respiratory disease
Nebulisation proprietary nebulisers must produce droplets of <3 microns to penetrate
to the lower respiratory tract. Nebulised drugs are not systemically absorbed and so
potentially nephrotoxic drugs may be used more safely by nebulisation. Generally
nebulise for 20 mins per day.
58
Psittacosis
Infection with Chlamydia psittaci; infects birds, cats, dogs, sheep. Difficult to diagnose affected birds may have marked illness, lameness only or appear clinically well. Latent
infection possible - disease appears when stressed.
Symptoms suggestive of Chlamydial infection;
•
bird listless and dull
•
respiratory signs (respiratory distress, respiratory clicks, auscultation, air sac
infection)
•
enlarged liver and spleen on radiography
•
elevated white blood cell count (>25 x 109/l), especially if concurrent heterophillic left
shift
•
ducks - conjunctivitis; turkeys and cockatiels - sinusitis
Aids to diagnosis
•
cloacal swab ELISA, PCR. Serology.
•
post-mortem findings in in-contact birds - serous membranes thickened (air
sacculitis, pericarditis)
•
signs of septicaemia in carcass
•
enlarged spleen, liver (radiography, endoscopy, post-mortem)
•
impression smear tests of parenchyma (liver, spleen, lung, kidney)and serosal (liver
and spleen) surfaces with Modified Ziehl-Nielsen for elementary bodies.
Zoonotic implications
•
warn owners of zoonotic risk, and make informed decision to treat or euthanase
•
symptoms in man - headache, fever, confusion, myalgia, non-productive cough,
lymphadenopathy
•
health status of owner should be taken into account (HIV, immunosuppressive drug
treatment)
•
adopt strict hygiene standards (wash hands with antiseptic after contact with bird,
wear masks)
Treatment
59
It is advisable to include Psittacosis treatment if the disease is suspected, even if not
diagnosed
treat under quarantine conditions, with plastic aprons, hats, masks and gloves for staff
a)Parenteral
Doxycycline 2%, 100 mg/Kg i/m (half dose either side of keel) and
Vitamin A injections. Treat with a 45 day course with injections on days 1, 8, 15, 22, 28,
34, 40, 45
repeat ELISA/PCR test (following stress/ prednisolone) a few weeks after treatment
b)Oral dosing
crush doxycycline tablets or ciprofloxacin in lactulose
Aspergillus
Aspergillus fumigatus is the most common species. A. flavus and A. niger less common.
Chronic respiratory infection or peracute death.. African Grey parrots, Blue fronted
Amazon parrots and mynah birds are susceptible pet species. Goshawks, Gyrfalcons
and penguins are also susceptible. As this organism is ubiquitous in the environment,
birds generally succumb to infection only when compromised by certain factors. These
factors include stress, malnutrition, age, antibiotic therapy, respiratory irritants or
concurrent disease. Both local and systemic forms occur. Clinical findings in an affected
bird include (in decreasing order); emaciation, respiratory distress, neuromuscular
disease, abnormal droppings, vocalisation changes.
Nasal aspergillosis - dry granuloma in one or both nostrils that causes erosion. Birds
may present with one very large nares
Tracheal or syringeal - severe dyspnoea, whistling sounds as breathe
Air sac form - diagnosis based on endoscopy, radiography
Lung form - animal can exsanguinate if granuloma invades a major vessel
Diagnosis
Haematology, serology, radiography, endoscopy, exploratory surgery. Fungal culture of
sinus flush, lung wash, air sac flush. Haematology changes associated with Aspergillosis
include; leucocytosis, heterophillia, monocytosis, lymphopaenia, non regenerative
anaemia, hyperproteinaemia, hypergammaglobulinaemia
60
Treatment
Surgical debridement and removal of plaques or granulomas if possible. Topical
treatment with antifungal, nebulisation, oral therapy. Amphoteracin B can be given
intratracheally. Itraconazole is the oral therapy of choice due to its low toxicity and high
efficacy (10mg/Kg). Nebulisation with clotrimazole (‘Canesten’ in propylene glycol) for 15
minutes daily in conjunction with oral itraconazole has been used successfully in a
number of parrots. Oral itraconazole at 10mg/kg for 6 weeks with nebulisation (e.g. with
F10 or IV antifungal solutions) once/twice daily for 20 minutes.
Sour Crop
Inflammation and ulceration of the crop lining. First signs; regurgitation and soiling of
beak. Crop fluid is foul-smelling, blood tinged or mucoid. Obtain cytology and microbial
culture and treat appropriately.
Tx milk out crop contents three times a day, treat with appropriate antimicrobials
Caused by Candida albicans or Trichomoniasis. Candida is a normal part of the gut flora
in healthy birds, so if implicated as pathogenic, look for predisposing factor. Can spread
systemically in susceptible birds ( e.g. young hand-reared psittacines)
Signsregurgitation, thickened crop (see also), distended crop, delayed emptying
Dxpalpation, visualise crop lesion (auroscope/endoscope) as white foci on mucosa,
‘Turkish towel’ appearance to crop mucosa, crop wash - culture and staining of sample,
deep mucosal scrapings, biopsy
Tx antifungal drugs or antiprotozoal drugs and supportive therapy
Note For flock control of candidiasis and Trichomoniasis, give chlorhexidine 2% in
drinking water.
Dermatology
Tassel Foot/Scaly Face
Cause Cnemidocoptes pilae. Only attacks older bird with underlying vitamin A
deficiency
Tx parenteral
ivermectin,
topical
evening
supplementation.
61
primrose
oil,
vitamin
injections
and
Pododermatitis/Bumblefoot
occurs in raptors primarily (and other exotic birds)
Cause inappropriate husbandry/perches, dietary deficiencies. Day old chicks are high
in cholesterol and low in calcium
Tx Ispagula husk (Isogel, Regulan, Metamucil) may lower cholesterol levels in birds fed
fatty foods (useful in parrots). Feed rodents , or wash eggs yolk from day-old chicks.
Radiograph foot- check sesamoid bone intact, if infection of bone consider surgery or
euthanasia. Antibiosis (cloxacillin, lincomycin), surgical drainage, correct diet, correct
husbandry
Feather Plucking
It is imperative that the patient undergo a complete diagnostic workup to eliminate an
organic cause of the feather plucking. The common causes are; boredom/neurosis, poor
quality feathers (nutrition, hormones, husbandry), folliculitis, feather mites, liver disease,
masses within the coelom. Blood haematology and biochemistry, radiography, faecal
examination and exploratory endoscopy/ surgery are required. If it is a behavioural
problem it is difficult to resolve. May also chew nails. Can progress to anorexia and
weight loss.
Dxhistory, cage size, social interactions, pattern of feather loss. Initially flight and contour
feathers are lost, but may become bald except for head.
Tx treat underlying problem if present. In cases of neurosis only; cause of the neurosis
must be corrected for any treatment regime to be successful.
•
Elizabethan collar. Allow bird to adapt to it in hospital before being discharged. Allows
assessment of follicular activity if still some doubt. Removed when normal feathers
have regrown (about 2 months). DO NOT BE TEMPTED TO MAKE COLLAR THE
PERMANENT SOLUTION.
•
improve plane of nutrition necessary for feather regrowth (especially protein, calcium,
energy)
•
change environment frequently, allow exercise, give branches to gnaw, increase
owner attention to bird. Provide hide so bird has privacy
•
bathe/spray daily (especially African Greys as they are very dusty normally)
•
discourage bird by placing in dark cupboard (ignoring it) or using water pistol.
Shouting is seen as attention (positive reinforcement).
62
If these points are not successful, medical therapy may be attempted;
Tranquillisers
diazepam (5mg/ml) at 2 drops/ 30 ml drinking water
Thyroid hormones start at high (moult inducing dose) 100mcg/ Kg thyroxine every
other day for 2 weeks, then reduce to a quarter for 4 weeks.
Dietary Deficiencies
Hypovitaminosis A
•
especially of larger psittacines maintained on exclusively seed diet
•
early cases
lethargy and unthriftiness only at first, then hypersecretion -> serous
nasal discharge, sneezing/coughing. Secondary respiratory diseases unresponsive
to treatment. May see metaplasia mandibular salivary gland only (small round mass
under jaw)
•
later cases
squamous metaplasia leads to single/multiple keratin cysts in mucus
glands in oral cavity, secondary bacterial oral infections, rhinoliths, xeropthalmia,
conjunctivitis, periocular abscessation, gout (due to renal tubule metaplasia)
Dxdietary history, clinical signs, biopsy of keratin cysts
Tx debride oral lesions, excise abscesses, surgically remove rhinoliths etc. Supply
vitamin A at 5-50 iu/g daily for 2-4 weeks. Improvement is seen within 3 days. Correct
diet.
Calcium Deficiency
Dxskeletal abnormalities (fractures, misshapen sternum), dietary Ca: P should be
>1.5:1, raptors raised on day old chicks (whole adult rodents best), brachynathism.
Hypocalcaemic tremors, tetany, fits. Egg retention (see later), shiny beaks (lack of
powder down), enlarged parathyroid glands at PME
Tx Nutritional supplementation, oral supplementation, Hypocalcaemic tetany 20%
calcium solution diluted to 10% with 5% dextrose. Also inject vitamin A as deficiency
likely and to encourage adequate absorption of calcium supplementation.
63
Reproductive Problems
Excessive Egglaying
Especially common in pet cockatiels
Tx do not remove the laid egg, encourage her to brood them. Reduce calorific intake (not
if already debilitated). Very difficult to cure medically- ovariosalpingotomy is possible.
Egg Retention
**avian emergency**
Tx warm the bird and increase humidity of environment. Within 60 minutes begin calcium
treatment, then oxytocin (see drug table). If the egg is not expelled, surgical access is
usually made possible by this treatment.
Viral Diseases
Psittacine Beak and Feather Disease (PBFD) Virus
A chronic disease, symmetrical feather dystrophy and loss, development of beak
abnormalities, death. Acute form (French moult) grossly dystrophic feathers in the first
moult.
transmission oral, intracloacal, intranasal (experimentally)
Dxgenerally birds aged <3 years, abnormal feather colouration, dystrophic feathers.
PCR test for viral DNA in whole blood
Tx None. Birds may live for several years with few or very deformed feathers.
Polyoma Virus
Budgerigars
neonates - sudden death, survivors have symmetrical feather abnormalities; dystrophic
primary and tail feathers, lack of down feathers on the back and abdomen. Similar to
PBFD however feather loss will resolve after several months.
Other psittacines
64
sudden
death,
death
after
depression,
weight
loss,
diarrhoea,
regurgitation,
subcutaneous haemorrhage, dyspnoea, polyuria. Chronic form manifests as weight loss,
intermittent anorexia, polyuria, recurrent infections, poor feather formation.
Transmission unknown, horizontal and vertical? feather dust?
DxCannot be distinguished clinically from PBFD. Cloacal swab for viral specific DNA
detection by PCR
Tx vitamin K (0.2 mg/Kg) for haemorrhaging birds. Immunostimulants? No successful
treatment found. Vaccine now available in USA.
Mycobacterium avium
This disease rarely affects housed pet birds but can affect those housed in an outside
aviary. It is a particular problem in waterfowl and zoo pheasants and other ground
feeding birds. There are PCR tests available for faecal testing and an ELISA for blood
testing. There is no recignised treatment other than disease control by culling positive
animals, keeping feed away from faecal contamination, good attention to hygiene to
prevent the disease building up in the environment.
Nursing the Sick Bird
•
Nutrition
-a high energy requirement. If hepatic function is compromised, Hycal
(Beechams) for fat free energy source. Fat free baby foods. Spirulina (algae) as
easily assimilable protein (crush tablet with water)
•
Hydration -gavage with Lectade (SKB), or electrolyte/probiotic (Avipro: Vetark)
•
Warm foods before administering via crop tube. Care not to overheat in microwave
or will cause crop burn.
•
Probiotics are useful e.g. Avipro (Vetark). Stressed/ill birds often lose commensal
bacteria from their short GIT.
•
Provide warmth without draughts, incubators are useful.
•
Place cage at shoulder level.
•
Darkness and quiet tends to sedate birds and reduces stress.
Short Avian Formulary
Antibiosis Dosage Guide
Drug
piperacillin
Form and Route
i/m
65
Dose (mg/ Kg)
200-100 tid
cefotaxime
gentamicin
amikacin
doxycycline
enrofloxacin
chloramphenicol
trimethoprim pot.
sulphonamides
i/m
i/m
i/m
i/m
oral
po i/m
i/m
po
nystatin
Amphoteracin
i/m
i/m
po
in drinking water
oral by gavage
intratracheally
itraconazole
ketoconazole
miconazole
orally
orally by gavage
i/m
Anthelmintic Drugs
Drug
fenbendazole
Form and Route
orally by gavage
metronidazole
in drinking water
levamisole
praziquantel
orally
s/c
as an
immunostimulant
s/c
orally
ivermectin
i/m or s/c
orally 1%
i/m or s/c
percutaneously
Miscellaneous Drugs
Drug
medroxyprogesterone
acetate (5%)
Form and |Route
i/m or s/c
oxytocin 10iu/ml
i/m
66
100 3-6 x day
2.5 bid
10-15 bid
100 once a week for 45d
25 bid
7.5 - 15
50 bid (budgerigar)
50 QID (parrots)
50 SID
25 bid
25 bid
5 bid
50 as tablet
20 mg/ l
300,000 - 600,000 iu/Kg bid x 7d
1 in 2ml water bid x 12d then
alternate days for 5 weeks
10 SID 4-6w
25-30 tid x 2w
10 SID x 6-12d raptors
20 SID 8-10d psittacines
Dose (mg/ Kg)
10-50. rpt 10d for nematodes,
daily for 3d for trematodes
+microfilaria
daily for 5d for capillaria
50 mg/l
10-20, rpt 14d
4-8
2 , 3 injections 4 days apart
5-10 as tablet, rpt 2-4w for
cestodes and nematodes
7.5 or 0.13 rpt in 2-4w
1ml diluted in 4.5 ml
polypropylene, give 0.1 ml/Kg
0.2 Can be toxic in small birds
1ml of 1% in 10ml polypropylene
glycol. One drop to back of neck
monthly
Dose (mg/ Kg)
5-10 to suppress persistent
ovulation
30 to stop regurgitation
3-5 iu once only for egg retention
delmadinone (Tardak)
dexamethasone 2mg/ml
i/m
i/m or i/v
doxapram hydrochloride
i/m
drops to tongue
bromhexine
i/m
powder 1%
multivitamins
vitamin A
calcium borogluconate
10%
frusemide
iodine
i/m
i/m
s/c i/m
pancreatin
powder/capsules
lactulose syrup
orally in soft food
i/m s/c
orally in drinking
water
orally by gavage
with ca borogluconate
1 (0.02 ml/30g)
0.3-3 or 0.15-1.5 bid shock/antiinflammatory
5-10
one drop for apnoea during GA
and to speed recovery from
ketamine anaesthesia
3-6
2g powder/l mucolytic and helps
antibiotics penetrate respiratory
mucosa
maximum dose is 20,000iu vitamin
A
1-5ml/Kg for egg retention and for
Hypocalcaemic tetany
0.15 bid
stock solution made with 2ml
Lugols iodine to 29ml water, one
drop to 100ml drinking water
as an aid in Tx of pan.
insufficiency, pancreatitis
0.25ml/ Kg appetite stimulant,
laxative
Mammals
ENCEPHALITOZOON CUNICULI
This common parasite is spread in urine and affects
Primarily the nervous system (brain and spinal cord) and kidneys. Hind
limb weakness and paralysis is a result of the inflammation surrounding the
parasite causing destruction of the nervous tissue. Other signs commonly seen with this
disease include a head tilt, fitting; loss of balance, tremors, kidney failure and bladder
weakness. Unfortunately once the rabbit develops severe clinical signs this can lead to
death.
A blood test can be carried out to measure antibodies that are produced by the rabbit if it
has been exposed to the disease at some stage in its life. 50% of healthy rabbits were
found to have antibodies to this parasite in a study carried out by E.Keeble (Keeble et al
The Veterinary Record 158:539-543 (2006), which makes it difficult to interpret the blood
67
results fully. More information indicating the stage of infection and immune response can
be obtained by taking two blood samples one month apart. If the antibody levels to
E.cuniculi are falling, this suggests that a recent history of infection or flare up of an
existing E.cuniculi infection has occurred. Rising antibody levels between the 2 blood
samples is more suggestive of a current active infection or flare up. However if the
antibody levels are the same at the first and second blood sample, it is difficult to
conclude too much. As we learn more about how this parasite affects the body, how the
immune system can deal with it and in some cases fully recover, we will be able to
interpret the results more accurately. Unfortunately at this stage we can only support
rabbits with the condition, because at present there is no specific treatment that will
reverse the damage caused by the presence of the parasite. Medication (Fenbendazole)
can slow or halt the rate of multiplication of the E.cuniculi parasite with in the body. (see
photo of rabbit having blood test for E.cuniculi antibodies)
Rabbit abscesses
Aetiology
Subcutaneous abscesses can result from periodontal disease, trauma, foreign bodies;
bacteraemia secondary to systemic disease including peridontal disease. Bacteria
usually isolated include Pasteurella multocida, Staphylococcus aureus, Proteus spp,
Pseudomonas aeruginosa, Bacteriodes spp and Fusobacterium, Streptococcus,
Escherichia coli, Corynebacterium pyogenes and Klebsiella have also been isolated.
Pulmonary abscess can result from chronic respiratory disease or also be secondary to
bacteraemia. Retrobulbar abscesses usually are associated with tooth root abscesses.
Clinical features and diagnosis
Rabbits form thick-walled abscesses that contain caseous, inpissated purulent discharge
in reaction to most bacterial infections. Their pus does not drain as in other species.
Abscesses can form anywhere in the body and are usually not associated with pyrexia
and not always painful. Diagnosis is made on historical and clinical findings.
Haematology and biochemistry may indicate systemic disease. Radiography should
always be carried out if there is a suspicion of osteomyelitis and as an aid to prognosis.
68
Ultrasonography may be useful to identify sinus tracts and foreign bodies as well as
delineate abscess margins, especially retrobulbar abscesses. Computer tomography
may be used in retrobulbar and middle ear abscesses.
Treatment and prognosis
Complete surgical excision, leaving the wall intact with a substantial margin, so that all
the contaminated tissue is removed is the recommended treatment. Excision of large
abscesses may require the use of skin flaps for closure of the defect. The use of
antibiotic-impregnated polymethylmethacrylate beads has been advocated following
excision, or where total excision is not possible, has been used to treat and prevent
reformation. Antibiotics that have been used include gentamicin, piperacillin, amikacin,
tobramycin and cefazolin/cephalothin although care must be taken to avoid oral
absorption of these antibiotics, as they have been associated with fatal enterotoxaemia.
The pus usually is sterile therefore always submit the abscess capsule or affected bone
for bacterial culture and antibacterial sensitivity, so that appropriate antibiotic therapy
post operatively can be used. Retrobulbar abscess may require enucleation. Abscesses
affecting limb bones or joints may require amputation. Where tooth root abscesses are
involved affected teeth must be extracted. Doxycycline gel (Doxirobe gel, Pharmacia and
Upjohn) has been used with good success in packing defects secondary to periapical
infection and abscess excision. Calcium hydroxide causes severe soft tissue necrosis
and therefore its use should be avoided.
Where complete resection is not possible the soft tissue and affected bone should be
debrided, flushing with antiseptic solutions, appropriate antibiotic therapy (systemic and
or local e.g. gentamicin injected into the capsule), hyaluronidase, honey (clear unboiled,
Manuka honey is reputed to have the most antibacterial properties) have all been used
to manage abscesses. Penicillin G Benzathine/ Penicillin G Procaine combination has
been used in a small number (n=10) of facial abscess cases with good success.
Dosages used were 75,000 units subcutaneously, every other day for rabbits weighing
less than 2.5 kg, and 150,000 units subcutaneously, every other day, for rabbits weighing
more than 2.5kg. However signed owner consent should always be obtained prior to
treatment as the fatal side effects of Penicillin in rabbits are well documented. Long-term
prognosis is improved if complete excision is achieved; if this is not possible reoccurrence is common and may require life-long antibiotic therapy and repeated
surgeries. Osteomyelitis carries a poor prognosis.
69
DRUGS USED TO TREAT CARDIAC CONDITIONS IN RABBITS
Drug
Dose (mg/Kg)
Route
Frequency
Frusemide
0.3-4
Enalapril
0.1-0.5
Glyceryl
trinitrate ointment
(2%)∝
3mm
Atenolol ∝
0.5-2
Verapamil* ∝
0.2
Diltiazem
Lidocaine
0.5-1
1-2 (2-4 IT)
Primary action
Loop
Diuretic
po, sc, im, iv
Every 12-24h
(reduce preload)
Every
24- ACE
inhibitor
48h(start
with (reduce
po
48h)
afterload)
Vasodilator
Topical: applied
(reduce
to inner pinna
Every 6-12h
afterload)
β-Adrenergic
po
Every 24h
blocking agents
Calcium channel
blocking agents
(enhance
po, sc, slow iv
Every 8h
diastolic function)
po
iv, it
Every 12-24h
Bolus
Calcium channel
blocking agents
(enhance
diastolic function)
Antiarrhythmics
Antiarrhythmics
(improve systolic
function)
Anticholinergics
Anticholinergics
Digoxin ∝
0.003-0.03
po
Every 12-48h
Atropine δ
0.05-0.5
sc, im
Bolus
∝
Glycopyrrolate
0.01-0.1
sc, im iv
Bolus
po Oral, sc Subcutaneous, im Intramuscular, iv Intravenous, it Intratracheal
∝
Not licensed for use in animals
* Verapamil is used to reduce or prevent adhesion formation following abdominal surgery
in rabbits. There are currently no reports of verapamil being used for treatment of
cardiac disease in rabbits.
δ
Ineffective in a high proportion of rabbits.
Rabbit respiratory disease therapeutics
Treatment of upper respiratory disease and prognosis
Resistance has been seen in bacteria other than Pasteurella species. If this is not
possible antibiotics which have been shown to be sensitive to Pasteurella multocida and
which currently have the least resistance include penicillin G, chloramphenicol,
erythromycin, tetracyclines, fluoroquinolones, novobiocin and nitrofurans. Antibiotics
which P.multocida is known to have resistance to include lincomycin, clindamycin and to
some degree streptomycin and sulphonamides. In severe infections the use of
parenteral, nebulised and topical antibiotics may be indicated. Nasolachrymal duct
flushing with sterile water or antibiotics is indicated in dacryocystitis. Non-steroidal antiinflammatory are essential to reduce inflammation in the narrow URT and analgesia is
essential as this condition is painful. Mucolytics (bromhexine, N-acetyl-cysteine) and
humidification are useful in the management of rhinitis. Assisted feeding is indicated if
70
anorexia occurs. Prognosis is dependent on severity of disease and response to
treatment.
Treatment of viral disease is supportive, but euthanasia may be indicated in severe
cases. Avoidance of allergens and irritants is important in all cases of respiratory disease
as these predispose the respiratory tract to infection. Nasal carcinomas carry a grave
prognosis. Foreign body removal by forceps or endoscopically and subsequent
antibiosis is indicated.
Treatment of lower respiratory disease
Antibacterial treatment of bronchopneumonia should ideally be based on culture
and sensitivity. In chronic cases antibiotic therapy may be required for months.
Treatment of bacterial pneumonia is similar to rhinitis. Humidification or nebulization will
reduce dyspnoea and aid absorption of antibiotics. These critical patients often require
intensive nursing and oxygen therapy. Prognosis will depend on the severity of the
disease and response to treatment.
Viral pneumonia is generally unresponsive to treatment and euthanasia on
humane grounds should be considered.
Removal of a thymoma via median stereotomy has been accomplished.
Radiation chemotherapy has also been used in a rabbit with thymoma. Thoracic
metastasis has a poor prognosis, supportive therapy with antibiotics and bronchodilators
may give temporary relief.
Allergic respiratory disease should be managed by elimination of the allergen
where possible, antihistamines can also be used to reduce inflammation.
Prevention of P.multocida can be carried out by serological screening and barrier
housing, to establish Pasteurella-free colonies in laboratory rabbits. Pet rabbits however
are unlikely to originate from Pasteurella-free sources. Carrying out serological
screening for P.multocida, quarantining positive animals and treating infected rabbits
may however reduce outbreaks and control disease in a multi-rabbit household. Several
vaccinations have been developed against P.multocida although none are currently
available for prevention of pasteurellosis. Careful attention to any contributing factors will
decrease the individual’s susceptibility to infection.
Vaccination against myxomatosis is available in the UK (Nobivac Myxo, Intervet),
a live attenuated vaccine containing Shope Fibroma virus that provides cross-immunity
against the myxoma virus. Vaccination should commence from 6 weeks of age. Boosters
are required every 6-12 months depending on risk. Effective insect control is essential to
reduce the risk of infection.
Treatment and Prognosis of rabbit ulcers
Therapy depends on the severity of the ulceration and whether the underlying cause
is detected. Rabbits with perforation and peritonitis have a very grave prognosis.
Symptomatic or prophylactic treatment could be considered in higher risk cases such as
females in late gestation, rabbits with anorexia, enteritis or chronic disease. This would
include decreasing acid production, protecting ulcerated mucosa, fluid therapy,
analgesia, antibiosis and supportive nutrition. Ranitidine partially inhibited basal acid
secretion (73%), and partially decreased pepsin secretion (37%). Cimetidine, however
was found to be ineffective in protecting against stress-related gastric lesions in a rabbit
model. Sucralfate (Antepsin) (25mg/kg per os every 8-12 hours) either a crushed tablet
slurry or viscous gel has been shown to bind to pepsin substrates in tissues resulting in
very effective prevention of experimental induced peptic esophagitis in rabbits and may
be effective in treating gastric ulceration.
71
Treatment and prognosis of rabbit /small herbivore gastrointestinal tract stasis and/or
ileus
Aggressive medical management is required to prevent further deterioration and
death. Nearly 10% of fundic ulcers were found to be associated with anorexia or caecal
impaction, in a survey of gastric ulceration in the rabbit. Hepatic lipidosis is a common
complication and cause of death in rabbits, with prolonged gastric stasis and ileus.
Rehydration, of both the patient and stomach contents, with both oral and intravenous
fluids may be required depending on the severity of the case, 100ml/kg/day is the
maintenance volume in the rabbit.
Analgesics, such as buprenorphine (0.01-0.05 mg/kg, subcutaneously, every 6-8
hours) or butorphanol (Torbujesic) (0.1-0.5mg/kg subcutaneously or intravenously, every
2-4 hours), in the first instance, and then once rehydrated, NSAIDS e.g., meloxicam
(Metacam) (0.1-0.6mg/kg subcutaneously or per os, every 24 hours) or carprofen
(Rimadyl) (2-4mg/kg subcutaneously, intravenously or per os, every 24 hours) are also
appropriate.
Prokinetics are required to stimulate GIT motility. Cisapride (Prepulsid) (0.5mg/kg
per os every 8-12 hours) a potent prokinetic, acts on 5-hydroxytryptamine (5-HT or
serotonin) receptors and facilitates and restores motility throughout the length of the GIT.
Dosing intervals for cisapride should be every eight hours. Cisapride was withdrawn in
2000, from several Western European countries, the United States and Canada,
because it was shown to be associated with a rare, but potentially fatal ventricular
arrhythmia (Torsade de pointes) in man, due to drug-induced delayed re- polarization
and prolongation of the QT interval. Similar characteristics have been characterized in
rabbit hearts and canine cardiac Purkinje fiber, but in vivo effects have not yet been
reported in dogs, cats or rabbits.
Metoclopramide (Emequel)(0.5mg/kg per os or subcutaneously every 8-24
hours), is a dopamine antagonist having both central (antiemetic and depressant) and
peripheral (prokinetic) effects. The prokinetic effects of metoclopramide are not as potent
as cisapride and are limited to the proximal GIT. Having prokinetic effects equal to
cisapride, and antacid actions makes ranitidine (Zantac) (2-5mg/kg per os every 12-24
hours) a very useful drug, in the author’s opinion, in the treatment of gastric stasis and
ileus. H2 receptor antagonists will reduce gastric acid, and have also been shown to have
a concentration dependent prokinetic effects on the rabbit stomach fundus and sigmoid
colon, the order of potency was ranitidine>famotidine>cimetidine .
Dimethicone (Infacol)(20-40mg/kg per os every 6 hours) may be useful if a large
amount of gas is present. Exercise will also stimulate GIT motility and should be
encouraged.
Nutritional support to reverse energy balance and stimulate motility can be
achieved by syringe feeding commercially available high fiber recovery diets e.g., Critical
Care for Herbivores (Oxbow Petlife International Ltd., Bury St. Edmunds, Suffolk, UK),
ground up rabbit pellets or pureed vegetables and grass, four-five times a day. A wide
variety of fresh vegetation should be offered daily, to encourage the rabbit to eat.
Nasogastric tubes are easily placed in a conscious calm or weak rabbit, in a similar
manner to that used in a cat. Radiography is always recommended to ensure the tube is
in the correct position. Some rabbits will tolerate the tube without an Elizabethan collar,
which will enable eating, caecotrophy and is less stressful. Blended and strained food
can then be fed; flushing with 5ml of water before and after feeding will keep the tube
patent. Nasogastric tubes can be left in place for several days. Antibiotic therapy such as
enrofloxacin (Baytril) (10-30mg/kg per os or subcutaneously, every 24 hours) is
advisable to help prevent rhinitis, which may develop if nasal tissue was traumatized.
72
Bacterial enteritis in rabbits/small mammals
Treatment and prognosis
Aggressive fluid therapy and supportive therapy is essential in these critical patients.
Metronidazole (Flagyl) (20mg/kg, per os, every 12 hours) is indicated. Cholestyramine
(Questran) (2g in 20ml water, by gavage, every 24 hours) has been shown to bind to
bacterial toxins, including clostridial cytotoxin and endotoxin in man. Enteroxemia and
mortality in rabbits, due to intravenous clindamycin, was prevented by cholestyramine
administration on day 1 or 3 of the study. Loperomide hydrochloride (Immodium)
(0.1mg/kg, per os, every 8 hours for first 3 days, then every 24 hours for 4th and 5th days
after the start of the diarrhea) and a high fiber diet may improve recovery. Prognosis for
recovery of mild cases, that can be treated with diet adjustment can be good, however
severe cases have a poor prognosis.
Future treatments under current study include probiotics. There is an incomplete
understanding of the mechanisms of probiotic activity; suggested mechanisms for
reduction of pathogens include competition for nutrients, competition for enterocyte
adhesion sites and production of inhibitory substances. Lactobacilli and enterococcus
have been studied in rabbits. Lactobacilli, in contrast with other mammals, are very
rarely found in the rabbit GIT microflora. Although some strains of lactobacilli,
L.fermentum were shown to have relatively resistant to pH 2 of rabbit gastric juice, lack
of adhesive capability may prevent them colonizing the rabbit GIT. Transfaunation of
fresh caecotrophs from healthy rabbits can provide the appropriate microflora to help
reestablish caecal homeostasis.
Treatment and prognosis of rabbit coccidiosis
Treatment Trimethoprim-sulfamethoxazole (Co-trimoxazole suspension) (30mg/kg per
os, every 12 hours for 10 days) has been shown to be effective. Prognosis is good in
mild cases and may result in lifelong immunity.
Treatment and prognosis of rabbit mucoid enteropthy
Non-specific supportive treatment is recommended. In cases of constipation the use
of frequent enemas has been described . Prognosis is poor. Prevention can be
achieved by feeding a high fiber, low carbohydrate diet .
Viral Haemorrhagic disease (VHD) (Rabbit Calicivirus Disease)
Aetiology
A calicivirus, originated in 1984 in China and then spread to Europe. It arrived in the
UK in 1992, transmission is by oral, nasal and parenteral, is shed in urine and faeces.
Fomites, birds and insects can be important vectors. Rabbits older than 2 months of age
are affected, if infected before this age they become immune.
Clinical features
Peracute disease results in death with in 24 hours. Clinical signs seen with acute
disease include depression, anorexia and lethargy, progressing to pyrexia, tachypnea,
cyanosis, abdominal distension and constipation or diarrhoea. End stage of the disease
is seen with hypothermia, collapse, seizures and epistaxis. High morbidity rates (70100%) and mortality rates (100%) are associated with VHD. Haematology shows
lymphopenia and thrombocytopenia, clotting factors reflect disseminated intravascular
coagulation (DIC), with prolonged thrombin and prothrombin times, and increased fibrin
degradation products. Hepatocytes are the predilection site for calicivirus, where it
replicates and causes necrotising hepatitis, death is due to DIC or liver failure.
Diagnosis, treatment and prognosis
73
A presumptive diagnosis can be made on historical, clinical and pathological findings.
A definitive diagnosis requires demonstration of the virus on electron microscopy.
Treatment is supportive, however is usually unsuccessful. Prognosis is poor. Prevention
by an attenuated vaccine is available in Europe (Cylap), commencing at 8-12 weeks old
with annual boosters. The virus is killed by 0.5% sodium hypochlorite or 1% formalin.
VHD is no longer notifiable in the UK.
Small mammal formulary
Due to the large variation in dose rates for different species, only a few common drugs are
listed below. For further information you are directed to the reference list.
(m=mouse, h=hamster, r=rat, g=gerbil, gp=guinea-pig, rb=rabbit, f=ferret)
Drug
Species
Dose
Ciprofloxacin
All
10mg/kg q12h po
Doxycycline
All
2.5mg/kg q12h po
Enrofloxacin
All
5 - 10mg/kg q12h
Gentamicin
5-8mg/kg/day divided q8-24h sc,im
Neomycin
50 - 100mg/kg q24h
Oxytetracycline
10 - 20mg/kg q8h po
Trimethoprim-sulphadiazine
30mg/kg q12 - 24h sc
Tylosin
10mg/kg q12h
Griseofulvin
All
25mg/kg q24h po
Buprenorphine
h g r m gp
0.05 - 0.1mg/kg q8-12h
rb
0.01 - 0.05mg/kg q8-12h
Butorphanol
m
1 - 5mg/kg q3-4h
r gp
2mg/kg q3-4h
rb f
0.1 - 0.5mg/kg q4h
Carprofen
rb f
5mg/kg q8-12h
Fentanyl/fluanisone
rb, gp
0.3-0.5ml/kg im/sc
Fent/fluan + midazolam
rb
0.3ml/kg im + 0.5 - 2mg/kg iv
Ketamine/medetomidine
rb
25mg/kg + 0.5mg/kg im
ADMINISTRATION OF SUBSTANCES
For each species, site of injection and maximum volume is given in the table below:
Species
Subcutaneous
Intramuscular
Intraperitoneal
Intravenous
Mouse
Scruff, 2 - 3ml
Quadriceps,
2 - 3ml
Lateral tail vein,
0.05ml
0.2ml
Hamster/gerbil
Scruff, 3 - 4ml
Quadriceps,
3 - 4ml
Not practicable
0.1ml
Rat
Scruff, flank, 5 - Quadriceps,
10 - 15ml
Lateral tail vein,
10ml
0.3ml
0.5ml
Guinea pig
Scruff, flank, 5 - Quadriceps,
10 - 15ml
Ear
vein,
10ml
0.3ml
saphenous vein,
0.5ml
Rabbit
Scruff, flank, 30 - Quadriceps,
50 - 100ml
Marginal ear vein,
50ml
lumbar muscles,
1 - 5ml
0.5 - 1ml
74
75
Infectious diseases in small mammals
Rabbit and rodent conditions
DISEASES
DISEASES OF THE SKIN
1. PARASITIC DISEASE
Ectoparasites are the most common cause of dermatoses in small mammals. Diagnosis is
achieved by taking skin scrapings : Remove hair from affected area, squeeze skin gently, swab with 10% KOH, scrape with a
blunted scalpel blade and mount material in 10% KOH for examination. Wipe skin with
water afterwards to remove remaining KOH. You can use liquid paraffin instead of KOH to
see live mites.
Demodicosis
Disease most commonly seen in hamsters, but reported in gerbil, guinea-pig and rabbit.
Non-pruritic alopecia and dry, flaky skin, usually on dorsum and flanks. Two types of mite in
the hamster - D. aurati (long and thin) and D. criceti (short and broad). Both present on
normal animals and disease is stress-related e.g. poor diet, housing, concurrent infection,
pregnancy, or associated with ageing.
Treatment: Address underlying condition. Ivermectin at 400 micrograms/kg can be effective,
repeated every 7 - 10 days. Alternatively weekly bathing with amitraz diluted to 100 ppm
until no live mites or eggs seen (this is rarely necessary).
Sarcoptic mange
Most commonly seen in guinea-pigs infested with Trixacarus caviae. Severe pruritus, selftrauma, alopecia, hyperkeratosis and acanthosis, usually on
dorsum. Pruritus can be
severe enough to lead to seizures. Again, disease is often stress-related e.g. pregnancy.
Treatment: Ivermectin 200-400 micrograms/kg sc; 3 injections 7 - 10 days apart.
Bathing with Gamma BHC weekly, or dipping in a 1:72 soln. of Tetmosol fortnightly (no
rinsing) are also effective.
All in-contacts and the environment should also be treated, as the mite can survive for a
while off the host. Life-cycle takes 14 days and transmission is by direct or indirect contact.
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Sarcoptic mites much more rarely seen in the other species. S. scabei in the ferret can
cause foot swelling.
Notoedres muris in the rat burrows into the skin of the ears, causing warty, papular lesions.
This can spread to the face, neck and genitalia as a result of grooming. This mite is often
difficult to detect even on deep scrapings, and a biopsy may be necessary. Morphologically
similar species have been reported in the rabbit and hamster.
Fur mites
Often asymptomatic, but can cause disease in the mouse, rat and rabbit. Cheyletiella
parasitovorax and Listrophorus gibbus in the rabbit and Chirodiscoides caviae in the
guinea-pig can occasionally cause hair loss and scaling on the dorsum. In the mouse and
rat Myopia musculi, Radfordia affinis and Mycoptes musculinis (mouse only) cause miliary
lesions round the head and neck. Mites can be just visible to naked eye, or detected by
sellotape test.
Treatment: as for Trixacarus.
Ear mites
Psoroptes cuniculi in the rabbit, Otodectes cynotis in the ferret. Severe pruritus, and in the
rabbit the ear canal fills with thick crusts. Lesions can extend to skin of ear and head.
Treatment: If extensive crusts soften with mineral oil for 2-3 days to avoid damage to lining
of canal. Acaricidal drops (e.g. GAC) for four weeks or ivermectin 400 micrograms/kg
repeated 3 times at 14-17 day intervals. Life cycle of Psoroptes takes 21 days and females
can survive off the host for several weeks. Treat all in-contacts and environment.
2.FUNGAL DISEASE
Rare in small mammals, but Microsporum and Trichophyton spp. can cause alopecia and
scaling and occasionally mild pruritus. Diagnosis by hair examination and fungal culture.
Don't forget zoonotic aspect.
Treatment: Enilconazole wash (Imaverol) twice weekly until two cultures negative. For
groups of animals environmental treatment with a spray of enilconazole soln 50mg per m2
twice weekly for 20 weeks. Griseofulvin 25mg/kg P.O. or 0.75mg/kg of feed(10g/kg of 7.5%
powder in dry feed) - expensive.
3.BACTERIAL DISEASE
77
Common. Often secondary to poor management.
Subcutaneous abscesses in rabbits and guinea pigs/chinchillas are usually caused by
Staph. aureus or Pasteurella and contain thick toothpaste-like pus. Lance, drain and flush
with 3% hydrogen peroxide, an antiseptic or antibiotic solution ( may need sedation with
fentanyl/ fluanisone for this). On the mandible infection often spreads to the bone and
systemic antibiotics also required. NB mandibular abscesses are usually associated with
underlying dental disease - bony involvement carries an extremely poor prognosis.
Cervical lymphadenitis in guinea-pigs usually caused by Strept. zooepidemicus - swelling
or abscessation of the cervical lymph nodes. Organism enters via URT or abrasions in oral
mucosa.
Treatment: Surgical removal of the affected gland is best, or else lancing and flushing of the
abscesses. At least fourteen days appropriate antibiotics.
Moist dermatitis due to Pseudomonas aeruginosa in rabbits is seen as a consequence of
chronic salivation due to dental disease. See a blue-green stain on fur.
Treatment: Clip hair, topical antiseptics e.g. chlorhexidine, change management (e.g. use
water bottles). Systemic antibiotics rarely required.
2.ENTERITIS AND DIARRHOEA
NB Rodents and Lagomorphs are unable to vomit.
Diarrhoea is a common presenting sign and it is often difficult to find the cause. General
supportive treatment in lagomorphs and rodents consists of rehydration (oral, S.C. or
I.P),hand feeding (e.g. Milupa), withholding of green food, provision of hay for rabbits and
guinea pigs, probiotics (commercial or live natural yoghurt). The value of probiotics is,
however, debatable as the lactobacilli will be killed by the low stomach pH. Products such
as " Duphalyte", a sterile solution of amino acids, electrolytes, dextrose and vitamins very
useful S.C. or orally. Multivitamins esp B complex if coprophagy absent. Vitamin C for
guinea-pigs. Liquidised fresh droppings from a healthy animal can be used to repopulate
the gut (transfaunation) and 0.25-0.5 ml of products used to repopulate cattle GI flora (e.g.
Vetrumex, Leocud) can be used in guinea pigs and rabbits. Motility modifiers such as
loperamide (0.1mg/kg P.O.), metoclopramide and cisapride, and kaolin-based products can
be of use. ONLY use antibiotics if you are sure you are dealing with a bacterial cause, as
these can cause diarrhoea and death from clostridial enterotoxaemia.
78
1.Dietary causes are very common. A sudden change of diet, feeding of lawnmower
clippings, large amounts of laxative plants (e.g. dandelion, groundsel) or mouldy/frosted
food are common scenarios.
Treatment: Remove offending item plus supportive therapy.
2.Bacterial enteritis:
a) E.Coli. Important cause of diarrhoea in rabbits and ferrets. Young animals usually
affected. Can cause septicaemia and sudden death.
b) Salmonella. Usually S. typhimurium or S. enteritidis. Acute, often haemmorhagic
diarrhoea, death, or chronic diarrhoea and weight loss. Best to destroy animal - zoonotic
aspect plus carrier if treated and recovers.
c) Yersinia (pseudotuberculosis). Transmitted to outdoor rabbits and guinea-pigs via wild
birds and rodents - infection is by eating contaminated food or through skin lacerations.
Acute septicaemia and death or chronic diarrhoea and weight loss. Can feel enlarged
mesenteric lymph nodes in a thin animal. Can infect the cervical lymph nodes. Treatment
not advised - zoonotic.
d)Clostridia. C. spiriforme normally present in small numbers, but in certain situations (e.g.
antibiotic administration) they proliferate and cause a fatal enterotoxaemia.
e)Tyzzer's disease. Bacillus (now Clostridium) piliforme (an obligate intracellular bacterium)
important in mice and gerbils but can affect the other species. Peracute death or acute
diarrhoea and death, esp. in weanlings. Organism exists in vegetative and spore forms and
cannot be cultured. Source of infection is usually spore-contaminated food or bedding.
Diagnosis on PM - necrotising hepatitis, enlarged mesenteric lymph nodes and thickened
ileum. Silver stain, Giemsa or PAS for organism. Treatment usually unsuccessful, but can
try oxytetracycline in the water 0.1mg/ml for 30 days to decrease morbidity.
f)Proliferative ileitis/ "wet tail" in hamsters is a common condition in which several
aetiological agents have been implicated, including Chlamydia tracheomatis and a
Desulphovibrio species. It generally affects 3 - 8 week old hamsters, but can be seen in
adults. Clinical signs include lethargy, anorexia, weight loss, abdominal pain and a watery
79
foul-smelling diarrhoea. Rectal prolapse and intussusception often ensue. The thickened
bowel loops can sometimes be palpated. Death is common within 24-48 hours. Definitive
diagnosis is at PM, with histopathology of the terminal ileum showing mucosal hyperplasia,
hypertrophy of muscle layers and presence of an intracellular curved bacillus (probably
Desulphovibrio). Treatment is often unsuccessful, but supportive therapy and oral
tetracycline or neomycin have been reported to be successful.
3. Viral enteritis
Rarely seen in pet rodents and lagomorphs. Aleutian disease in ferrets can cause melaena
(see later)
4.Parasitic enteritis
a)Protozoa. Coccidiosis in rabbits and guinea-pigs (Eimeria spp.) is usually secondary to
poor husbandry. Detect oocytes in faeces.
Many different species of Eimeria have been identified in the rabbit. With predominance
of Eimeria perforans, E.media and E. magna in domestic breeding colonies wide spread.
Transmission is by ingestion of sporulated oocysts. It is generally accepted that
caecotrophy is not involved in the transmission of infectious oocysts. Prepatent periods
for the Eimeria species range from two to ten days, and sporulation requires 22 hours at
20 ºC for E.perforans and 70 hours for E.piriformis.
Clinical features Intestinal coccidiosis is most often a subclinical disease in adult
immunocompetent rabbits. Co-infection with other enteropathies, immunosuppression or
a naive immune system, dose of infection and species of Eimeria are all predisposing
factors to clinical disease. Clinical signs include: weight loss, mild to severe intermittent
or continuous haemorrhagic diarrhea, dehydration and occasionally intussusceptions.
Death is usually associated with secondary bacterial enteritis and dehydration. Ileo-ileal
intussusception suspected consequent to hyperperistalsis induced by E.perforans
infection has been reported.
Diagnosis Coccidiosis is presumptively diagnosed by finding oocysts on fecal flotation.
Even on repeated fecal examination, small numbers of oocysts does not determine their
clinical significance. Definitive diagnosis is based on histopathological findings.
Trichomonas, Entamoeba and Giardia can occasionally cause diarrhoea.
Treatment: Metronidazole 20 mg/kg daily for 7-10 days S.C. (Torgyl) or Flagyl suspension 1
ml in 150 ml drinking water, or dimetridazole.
80
b)Helminths. Rarely cause disease. Use benzamidazoles for nematodes, praziquantel or
niclosamide for cestodes.
DISEASES OF THE RESPIRATORY SYSTEM
Respiratory disease is probably the most common presenting sign in these species. Clinical
signs include nasal discharge, sneezing, dyspnoea, "rattling" respiratory noise, coughing.
Don't forget that in rodents a red oculonasal discharge is not blood but a porphyrin-stained
secretion from the Harderian gland that occurs with any stress/illness. Underlying chronic
respiratory disease is probably the reason for most anaesthetic deaths in these species.
1.Bacterial respiratory disease
Pasteurella multocida and in guinea pigs Bordetella bronchiseptica are the most common
causes of bacterial "snuffles" (rhinitis, sinusitis) and pneumonia. Pasteurella pneumotropica
is the main respiratory pathogen of rats and mice. These agents can also cause otitis
media and interna, abscesses and metritis. Other agents that can cause pneumonia are
Klebsiella, Streptococcus and Pseudomonas. Anorexia and depression will occur in severe
cases. Pasteurella and Bordetella are often present in symptomless carriers, and overt
disease is usually stress-related.
In rats and mice Mycoplasma pulmonis is a common cause of respiratory disease. NB
rabbits will mouth-breathe, rodents will not.
Treatment: Appropriate antibiosis. Supportive treatment in severe cases. For dacryocystitis,
cannulation and flushing of the nasolacrimal ducts is essential, under sedation. Instil local
anaesthetic eye drops before inserting a nasolacrimal cannula in the single punctum in the
medial aspect of the lower lid, and flush the duct through with sterile saline. Permanent
blockage of the duct can be due to a congenital deformity (dwarf breeds) or impingement
by tooth roots (see dental disease).
2.Viral respiratory disease
Viral disease is usually of little importance in pet situations, but can be a problem in
laboratory colonies. Sendai virus is practically endemic in pet rats and mice.
DISEASES OF THE MUSCULOSKELETAL AND NERVOUS SYSTEM
FITS/EPILEPSY
81
Reported in all species. Thought to be hereditary in gerbils. Severe Trixacarus in guinea
pigs can cause fits.
TORTICOLLIS
Seen in all species, but especially rats. The most common cause is otitis media/interna due
to infection. Mycoplasmosis in rats and streptococcus in guinea pigs. Rabbits –
toxoplasmosis, Encephalitozoon Cuniculi, meningitis, brain abscess, middle ear
infection/abscess, trauma, tumour.
Signs- classic head tilt, circling, rolling and nystagmus. Can often see pus at base of ear
canal. Medical treatment is often unrewarding but in acute cases steroids and antibiotics
can be effective. Bulla osteotomy is possible in large rodents, rabbits and primates, after
confirmation of tympanic bulla involvement by radiography.
82
Non-infectious diseases in small mammals
NEOPLASTIC DISEASE
Common in small mammals - most of the tumours seen in dogs and cats have been
reported.
Mycosis fungoides in hamsters is a cutaneous T-cell lymphoma causing pruritus, alopecia,
plaques and nodules. Diagnosis by biopsy. No treatment.
Melanomas in hamsters are also common.
Mammary tumours are the commonest tumour in rats and mice. They are usually very
rapidly growing, and surgical excision is essential. In rats they are usually benign
fibroadenomas, but in mice are more likely to be more malignant carcinomas and
adenocarcinomas
Ventral abdominal sebaceous gland adenoma/adenocarcinoma in gerbils. Often ulcerate,
surgical excision essential.
ENDOCRINE DISEASE
Persistent oestrus in ferrets can cause symmetrical alopecia. Treatment: Spaying, HCG
(100 IU im, repeated in 1 week if the vulvar swelling has not started to regress after 3 - 4
days), or mating to a vasectomised hob. Supportive therapy for the associated anaemia,
including blood transfusion if PCV <15%.
Hyperadrenocorticism in ferrets and hamsters causing alopecia and swollen vulva(ferrets).
In ferrets, hyperadrenocorticism differs from the condition in dogs. It is always adrenaldependent, and serum cortisol levels are rarely elevated. Instead, plasma androgens
and/or
oestradiol and/or 17-hydroxyprogesterone levels are elevated. The ACTH
stimulation test and dexamethasone test cannot be used to establish a diagnosis. This
condition is rare in ferrets in the UK, but very common in the USA.
Alopecia during pregnancy and after parturition is often seen in intensively-bred guineapigs.
Cystic ovarian disease in ageing guinea-pigs can cause a hormonal alopecia. (NB cystic
ovaries can also be an incidental finding). Treatment of choice is ovariohysterectomy. Some
success has been reported with HCG every 7 days for 1 - 3 weeks.
ENVIRONMENTAL AND BEHAVIOURAL DISEASE
83
Barbering
Seen in all species. Chewing of fur and whiskers by cage mates or occasionally self. In
mice often due to overcrowding/lack of bedding. In guinea-pigs can be due to lack of
dietary fibre, or over-zealous grooming of young by sows.
Self-plucking can cause gastric hairballs in rabbits, and plucking from the dewlap is a
normal nesting behaviour in does.
Nasal dermatitis in gerbils is secondary to hypersecretion of the Harderian gland posterior
to the globe. Porphyrin pigment in the secretion is thought to be a skin irritant and leads to
self-trauma. Hypersecretion is a response to stress, e.g. overcrowding, too high humidity.
Bald nose can also occur on animals that burrow vigorously or rub their noses on the wire if
fed by cage-top feeders.
Treatment: Topical antibiotics. Address underlying stressors. Inclusion of a sand bath in the
cage allows gerbil to remove excess secretions.
Ulcerative pododermatitis (sore hocks) in rabbits and guinea pigs is caused by keeping on
mesh floors, wet bedding, obesity. Ulcerative lesions secondarily infected with Staph.
aureus. Predisposing factors must be addressed. Resolution of lesions is often difficult and
can mean bandaging for several weeks.
Flystrike in rabbits and guinea-pigs kept outdoors. Obese and old rabbits especially
susceptible as cannot reach anus to eat soft mucus-covered caecal pellets at night, so
perineum becomes caked with faeces. Dental disease will also lead to lack of coprophagy
and caking of caecotrophs. Rabbits are
very susceptible to toxic shock from larval
secretions and will require supportive therapy.
Treatment: Cleansing with an antiseptic solution and removal of maggots. Dilute insecticidal
shampoo can be used or ivermectin to kill any further larvae. Prevention is by frequent
examination, fly control and regular clipping/cleaning of perineal region.
UROLITHIASIS AND CYSTIC CALCULI
Seen in guinea pigs, and occasionally the smaller species. Precipitates are normal in the
alkaline urine, usually calcium carbonate, but stones can occur. Radiography is essential
for diagnosis and any animal presenting with recurrent cystitis should be radiographed.
Often just a diffuse radiodense “sludge” can be seen in the bladder. Surgical removal and
84
fluid therapy are usually indicated. If just “sludge” is present, this can sometimes be flushed
out via catheterisation. Renal calculi are also found occasionally - no medical treatment
other than antibiotics for secondary/primary infection then surgery if possible.
PREGNANCY TOXAEMIA/KETOSIS
This is mainly seen in guinea-pigs and rabbits. Obese pregnant animals are usually
affected, as the name suggests, but obese males and non-pregnant females can also
succumb. Two forms occur; a toxic form in obese pregnant animals where foetal
displacement causes impaired uterine blood supply followed by ischaemia, foetal death and
DIC, and a true metabolic form initiated by a stressor such as fasting or transport. Clinical
signs are depression, anorexia, abortion, salivation, convulsions, coma and death. Ketones
may be detectable in the breath, and ketonuria may be present. Post mortem shows
hepatic lipidosis. Treatment involves administration of glucose or dextrose-containing fluids
or propylene glycol, corticosteroids and calcium gluconate. Prevention is by avoiding
obesity and minimising stress.
Dental disease
Aetiology
There are several causes of malocclusion, which is the most common dental
abnormality seen in pet rabbits. Mandibular and maxillary abscesses associated with
dental infections are common. Periodontal disease and pulpitis are often involved,
especially in cases of iatrogenic longitudinal fractures caused by teeth clipping.
Congenital malocclusion first presents at 8-10 weeks of age, although may
only be noticed at 12-18 months of age. Breed predispositions of mandibular
prognathism include some dwarf and lop-eared breeds. Primary incisor malocclusion
and elongation, with the mandibular incisors becoming straighter
due to lack of
occlusion, this cannot be corrected, and maxillary incisors forming spiral curvatures due
to occlusion with the mandible, but no dental wear, and may penetrate the palate or
cheek if left untreated.
Acquired malocclusion is mainly seen in adults. Inadequate dental wear is a
common cause where rabbits are fed a high carbohydrate low fiber diet resulting in
elongation of both root and crown. Incomplete wear and the curvature of the cheek teeth
results in spike formation on the lingual occlusal surface of the mandibular teeth and the
85
buccal occlusal surface of the maxillary teeth. This elongation of the cheek teeth
prevents normal occlusion and therefore dental wear of the incisors resulting in
secondary incisor elongation and malocclusion. Calcium deficiency due to selective
feeding when offered excessive quantities of coarse-mix food can lead to alveolar bone
resorption and tooth loosening, and will enhance the progression of dental resorption.
Traumatic injury including mandibular symphysis separation, temporomandibular joint
subluxation, mandibular ramus fractures, tooth fractures with subsequent pulp exposure
and tooth root abscess formation are also commonly seen.
Mandibular osteosarcoma, rarely reported in the rabbit, seen mainly over six
years of age, although has been reported in an 18-month-old, affects the normal
anatomy of mandible, and therefore the occlusal plane.
Gastric ulceration
Aetiology and clinical features
Gastric ulceration was observed in 7.3% (n=1000) of rabbits, at post mortem
examination. Fundic ulceration was a relatively common finding (53 of 73 cases), and
these rabbits were also found to have other clinically significant disease, including
anorexia, enteritis, typhlitis, intussusception and bronchopneumonia. Prevalence
increased with age (15% were over 2 years of age) and was also seen more commonly
in females. A suggested etiology was stress-induced ulceration, as a consequence of
stress of disease. Similar lesions were reproduced with intraperitoneal injection of
adrenaline, in rabbits. Another mechanism for fundic ulceration is hypovolaemic shock,
where lesions can develop with in three hours.
Fundic ulcers occurred as small,
multiple, shallow erosions of the gastric mucosa, and none were perforated.
Pyloric ulcers mainly occurred as single lesions, up to 1cm in diameter.
Perforation and peritonitis was associated in 70% of the pyloric ulceration cases, and
this was the only lesion of clinical significance found at post mortem examination. Only
one case was associated with gastric impaction, the others mainly died during parturition
or in the immediate post-parturient period. Peak incidence was in six to nine-month-old
rabbits (60% of total cases). The abdominal contractions during parturition may have
precipitated the gastric perforations in these cases.
Anorexia can be the principle sign; bruxism and affected rabbits may be reluctant
to move indicating severe pain. Melena is seldom seen in the rabbit. In some cases
86
clinical signs due to anemia and hypoproteinemia may be seen (pale mucous
membranes, dyspnoea, weakness, collapse and shock). Some ulcers may perforate and
then seal rapidly by adhesions, forming abscesses with in the gastric wall.
Diagnosis
Signs of acute abdomen and sepsis may be seen in rabbits with perforation and
peritonitis, and there may be evidence of peritonitis on plain radiography.
Ultrasonography can be useful in detecting gastric wall thickening associated with
infiltrative disease (e.g. lymphoma) Endoscopy is the most sensitive and specific tool for
diagnosing gastric ulceration, although in most cases the rabbit is unlikely to be stable
enough for general anesthesia at the time of presentation.
Treatment and Prognosis
Therapy depends on the severity of the ulceration and whether the underlying cause
is detected. Rabbits with perforation and peritonitis have a very grave prognosis.
Symptomatic or prophylactic treatment could be considered in higher risk cases such as
females in late gestation, rabbits with anorexia, enteritis or chronic disease. This would
include decreasing acid production, protecting ulcerated mucosa, fluid therapy,
analgesia, antibiosis and supportive nutrition. Ranitidine partially inhibited basal acid
secretion (73%), and partially decreased pepsin secretion (37%). Cimetidine, however
was found to be ineffective in protecting against stress-related gastric lesions in a rabbit
model. Sucralfate (Antepsin) (25mg/kg per os every 8-12 hours) either a crushed tablet
slurry or viscous gel has been shown to bind to pepsin substrates in tissues resulting in
very effective prevention of experimental induced peptic esophagitis in rabbits and may
be effective in treating gastric ulceration.
Gastric stasis and gastrointestinal ileus
Aetiology
Gastric stasis is primarily an acquired disorder of decreased motility. Generalized
ileus is a common continuation of this condition and may arise from mechanical
obstruction or from defective propulsion. Mechanical obstruction (e.g. dehydrated
impacted ingesta secondary to chronic dehydration, foreign bodies, infiltrative lesions)
cause delayed gastric empting. Abnormalities in myenteric neuronal or gastric smooth
muscle function or contractility result in defective propulsion. Primary factors associated
with these functional disorders include anorexia, high-carbohydrate/low–fiber diet, post-
87
surgical adhesions, lack of exercise, toxin ingestion (lead). Secondary factors include
pain and environmental stressors such as proximity of predators or a dominant rabbit,
change in group hierarchy, loss of a companion, change in housing, routine or diet,
transport, extremes of temperatures or humidity. Anorexia and chronic dehydration are
both causal factors and consequences of gastric stasis and ileus. Systemic dehydration
leads to gut content dehydration and impaction of normal stomach contents, which
includes loose hair lattices or trichobezoars. Clinical features
Gradual decrease in appetite leading to anorexia (days-weeks), decreased size and
amount of fecal pellets, gradual progression from bright and alert to depression,
dehydration and death.
Diagnosis
The history and clinical findings, of a firm, dough-like stomach on palpation, allow
a presumptive diagnosis of gastric stasis and ileus and are suggestive of non-obstructive
disease. Although, advanced cases do not permit differentiation between obstructive and
non-obstructive stasis and ileus. Plain radiography in early cases reveals a mass of hair
and food, appearing similar to normal ingesta. As the impaction in the stomach and
occasionally caecum develops, a gas halo is often seen around the compacted material.
Large amounts of gas are seen through out the gastrointestinal tract (GIT) as a result of
ileus. A definitive diagnosis can only be made on exploratory laparotomy, however this is
a high-risk procedure in these already metabolically unstable rabbits.
Treatment and prognosis – other lecture
Mucoid Enteropathy (Rabbit Epizootic enteropathy)
Aetiology
Mucoid enteropathy is an idiopathic, wide spread, condition resulting in goblet cell
hyperplasia and excessive mucous production within the intestinal tract. Mucoid
enteropathy is mainly seen in young rabbits of four to 14 week old rabbits, although
there have been reports of older rabbits. Mucoid enteropathy may occur concurrent with
other enteropathies. Lesions of mucoid enteropathy have been found associated with
cecal hyperacidity due to abnormal volatile fatty acid production or absorption and
dysbiosis, fiber deficient diet and dysautonomia.
Clinical features
88
Associated clinical signs that have been reported, include anorexia, depression,
abdominal pain and distention, weight loss, dehydration, hypothermia, diarrhea initially,
progressing to mucus excretion, or constipation and palpation of a firm, dough like, large
caecum. Acute mortality can occur within 1-3 days, reaching rates of 30-80%.
Diagnosis
Presumptive diagnosis can be made on history and clinical signs, although may
mimic other enteropathies. Radiography may show evidence of cecal impaction and in
later cases evidence of gastric and intestinal stasis. Definitive diagnosis is on post
mortem findings of copious intestinal mucous and goblet cell hyperplasia.
Treatment and prognosis
Non-specific supportive treatment is recommended. In cases of constipation the use
of frequent enemas has been described . Prognosis
is poor. Prevention can be
achieved by feeding a high fiber, low carbohydrate diet .
Dysautonomia and caecal impaction
Aetiology
Dysautonomia in the rabbit is an idiopathic condition that causes loss of autonomic
nervous system function. Twenty rabbits with clinical signs of mucoid enteropathy were
later confirmed on post mortem examination to be dysautonomia .
Clinical features
Dysautonomia is associated with clinical signs of gastrointestinal stasis and
autonomic nerve deficits. Symptoms include dry mucous membranes and conjunctiva,
dilated pupils, bradycardia, urine retention and overflow incontinence, dilated, firm,
impacted colon, proprioceptive deficits and loss of anal tone. Accumulation of food in
mouth and dysphagia and evidence of lower respiratory disease due to aspiration
pneumonia, secondary to dysphagia and megaoesophagus may also be seen. This
condition is associated with a high mortality in all affected species.
Diagnosis
A presumptive diagnosis can be made on clinical signs. Radiography of the thorax
and abdomen may reveal evidence of aspiration pneumonia, megaoesophagus,
impacted colon and a large bladder. Absent tear production can be demonstrated with a
Schirmer tear test, average tear production in rabbits is 5mm/min ± 2.4mm/min .
Dramatic miosis within 45 minutes occurs in dogs in response to diluted (0.1%)
pilocarpine (Pilocarpine), due to denervation hypersensitivity.
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Definitive diagnosis requires demonstration of the characteristic lesions of chromolytic
degeneration of autonomic neurons, found on histiology and electron microscopy, similar
to equine grass sickness and feline and hare dysautonomias, at post mortem
examination.
Treatment and Prognosis
Supportive treatment includes fluid therapy, force-feeding, eye lubrication, enemas
and bladder emptying. Bethanechol (Myotonine)(0.04mg/kg) enables many affected cats
and dogs to void urine normally and completely. Prognosis is poor, although in other
species some animals have spontaneously recovered.
Hepatic lipidosis
Aetiology
Anorexia is the primary cause of hepatic lipidosis, development is especially rapid in
obese animals. Hypoglycaemia develops rapidly in periods of anorexia as a result in
decrease glucose absorption and volatile fatty acid production by the caecal microflora.
This stimulates lipolysis and mobilisation of free fatty acids from adipose tissue to the
liver. The liver metabolises them into ketones. When in excess, ketoacidosis develops.
Both liver and renal failure are seen due to fat accumulation in these tissues.
Clinical features and diagnosis
Clinical signs include depression, anorexia, salivation, disorientation, ataxia, seizures
and death. Hepatomegaly may be detected on abdominal palpation, however care must
be taken as these livers are very friable. Presumptive diagnosis can be made on
historical
and
clinical
findings.
Serum
biochemistry
reveals
hypoglycaemia,
hyperlipaemia, metabolic acidosis raised liver parameters and azotaemia. Radiography
and ultrasonography may reveal hepatomegaly. Definitive diagnosis requires FNA or
biopsy and histopathology of the liver. Although, this is not recommended in these critical
patients.
Treatment and prognosis
Aggressive supportive treatment to reverse the negative energy balance is essential
in these patients. Fluid therapy and nutritional support are indicated. The underlying
cause of the anorexia must also be addressed. Prognosis is guarded to poor once
neurological signs have developed.
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Cardiac disease in rabbits. The approach, clinical signs and diagnostics are similar to
other mammals (radiograph, ultrasonography, ECG), see Notes taken from Reusch, B.
(2005) Investigation and management of cardiovascular disease in rabbits. In Practice
27, 418-425
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