PROCEEDINGS OF THE
NORTH AMERICAN VETERINARY CONFERENCE
VOLUME 20
JANUARY 7-11, 2006
ORLANDO, FLORIDA
SMALL ANIMAL EDITION
Reprinted in the IVIS website (http://www.ivis.org) with the permission of the NAVC.
For more information on future NAVC events, visit the NAVC website at www.tnavc.org
Exotics — Avian
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RATITE MEDICINE AND SURGERY
Brian Speer, DVM, Dipl. ABVP (Avian Practice), ECAMS
Medical Center for Birds
Oakley, CA
Ratite birds are a loose group of birds that share the
common characteristics of being large, flightless, and
ground-dwelling birds. The group consists of the ostrich,
emu, cassowary, rhea, and kiwi. These birds have a
sternum that lacks a keel and is flat. All ratite birds
originate from the southern hemisphere, all can swim,
and males all have a protrusible phallus. Their anatomy
and physiology are quite unique in many ways, as are
many aspects of their medicine and surgery.
The ostrich is an African bird and is represented in the
order Strutioniformes by a single genus and species,
Struthio camelus. There are four subspecies recognized,
and their descriptions are based on the male bird. There
is a hybridized ostrich, which was generated by
interbreeding three of these subspecies, and this bird is
referred to as the African Black, or domestic ostrich.
An adult male may stand 2.4 meters (8 feet) and weigh
over 160 kg (350 pounds). Females (hens) usually weigh
slightly less than the male (roosters or cocks). The adult
male ostrich has black plumage, while the female is gray
or brown. A breeding group consists of one male and
one to four females. Puberty is reached at two years of
age, but full reproductive maturity is not reached until
four years of age. Secondary male sex characteristics of
the male include reddening of the beak and legs
(coloring up), vocalization (roaring or booming), and
territorial or sexual displays (kanteling). Secondary
female characteristics include brown-gray plumage and
the behavior of wing fluttering and lowering the head and
pecking at air (fluttering and clucking). The male and
female ostrich share incubation duties, with the male
often incubating at night and the female incubating
during the day. Both adults brood and rear the chicks.
The emu is an Australian bird represented in the order
Strutioniformes by the single genus and species,
Dromiceius novaehollandiae. Emus reach up to
1.8 meters in height (6 feet), and weigh up to 60 kg
(150 pounds). Emus are short day breeders, with a
breeding season that lasts from October to March in the
United States. Breeding activity occurs most commonly
in the early morning and evening hours. The mature
male produces a "grunting" sound and the female
"booms" or "drums." The male incubates and rears the
chicks.
The rhea is a South American bird represented in the
order Strutioniformes by two genera, Pterocnemia and
Rhea. Rheas may stand 1.5 meters (5 feet) tall and
weigh up to 38 kg (80 pounds). The male performs
courtship displays, builds the nest, incubates, and rears
the chicks. Several females may lay in the nest
established by the male. No lasting pair bonds are
formed. The male collects these eggs for about one
week, then initiates incubation.
The cassowary is native to northern Australia, New
Guinea, and its adjacent islands and is represented in
the order Struthioniformes by the single genus,
Casuarius. Cassowaries are dense forest dwellers, and
have earned a reputation for aggressive behavior. The
female may reach 1.5 meters in height (5 feet) and
weigh as much as 85 kg (187 pounds). Males generally
weigh less than the females. The female cassowary is
usually as solitary bird. Males will incubate and rear the
chicks.
The kiwi is a New Zealand bird and is represented by
the single order, Apterygiformes, and the genus Apteryx.
Kiwis are nocturnal birds. A single, large egg is laid in an
underground burrow.
ANATOMY
Integument
The skin of these birds is relatively thick along the
legs and body, but relatively thin along the neck. The
medial digit of the cassowary has a large spike-shaped
nail that can be used for fighting. The head of the
cassowary is covered with a bony, horn-covered casque
which grows continuously throughout life. This casque is
absent at hatching. The ostrich thigh is devoid of
feathers. Emu and cassowary feathers have a double
rachis. Apteria are present along the lateral body wall of
the ostrich and the rhea, but these areas are fully
feathered in the emu and cassowary. The primary
remiges of the cassowary lack barbs, and almost appear
thorn-like.
Musculoskeletal System
All ratites have a raft-like sternum, with no keel bone.
The thoracic girdle of the ostrich consists of a fused
scapula, coracoid, and clavicle attached to the cranial
sternum. Ostrich and rheas have large wings; emus and
cassowaries have rudimentary wings. The pelvic girdle
consists of ilia that form an inverted osseous shield over
the top of the fused synsacral vertebrae. In the ostrich,
the ischial and pubic bones project caudally to fuse and
then turn ventrally and cranially to form a pubic
symphysis. In the other ratite species, the ischial and
pubic bones are separate and there is no pubic
symphysis. The patella is absent in ratites. The ostrich
may have a small bone in the tendon of insertion of the
muscle on the cnemial crest of the tibiotarsus. In the
ostrich and emu, one of the tarsal bones remains
unfused to the contiguous bones and its location gives
the radiographic appearance of a patella. The only
pneumatized long bone in the ostrich and emu is the
femur. The rhea, emu, and cassowary have three toes
(digits 2, 3, and 4). The ostrich has only two toes (digits
3 and 4). The third digit of the ostrich is the large toe.
The metatarsal-phalangeal joint is suspended so that the
standing weight is born entirely by the digits.
Gastrointestinal System
There is no crop in any ratite bird. The proventriculus
of the ostrich is large, dilated, and thin walled; glands are
restricted to a patch on the greater curvature. The distal
end of the ostrich proventriculus passes dorsal to the
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gizzard (ventriculus) and empties into the ventriculus on
the caudal aspect. The large opening between the
proventriculus and ventriculus makes it possible to
remove ventricular foreign bodies from an incision in the
proventriculus. The ostrich ventriculus is a thick-walled
organ and is situated to the left of the midline at the
caudal border of the sternum. Many ventriculi normally
contain small stones. The koilin normally is greenish to
brownish due to diet and refluxed bile. In the rhea, the
proventriculus is a small, dilated structure cranial to the
ventriculus. Glands are limited to a thickened dorsally
located patch. The ventriculus is elongated. The koilin
covers the surface of both the proventriculus and the
ventriculus. The rhea ventriculus is located slightly left of
the midline, but more caudal than in the ostrich. In the
emu and cassowary, the proventriculus is large and
spindle shaped. The ventriculus is slightly larger and
less heavily muscled. The cassowary proventriculus
lacks a koilin. the orifice into the duodenum is on the
right side in all species. Ratites all have paired ceca. The
ceca are long and sacculated in the ostrich, moderately
long in the rhea, and short and nonfunctional in the emu
and cassowary. The colon of the emu is short. The colon
of the ostrich is voluminous to provide digestion of fiber
and fluid absorption. The gallbladder is absent in the
ostrich, but present in the emu and rhea.
Respiratory System
Respiration occurs in all ratite birds by lateral
excursions of the chest wall. Ratite birds have complete
tracheal rings. In the emu, the complete tracheal rings
are interrupted by a 6- to 8-cm-long cleft on the ventral
surface of the trachea 10–15 cm cranial to the thoracic
inlet. A thin membrane covers the cleft in the chick, but
as the bird matures, an expandable pouch forms cranial
to the cleft. Air can be directed into the pouch, expands
the neck and produces the booming or drumming sound
heard in the female emu. Air sac space is greatly
diminished in these birds compared with flighted
species. Panting may occur in heat stress, and body
temperature is maintained by evaporative water cooling
from the trachea, air sacs, and gular area of the pharynx.
The nostrils of the kiwi are located at the end of their
elongated beaks.
Reproductive System
In ratites females, usually only one ovary develops
with the exception of the brown kiwi. In the kiwi, two
functional ovaries normally occur and the single left
oviduct is reported to be specially positioned and shaped
to receive oocytes from both the right and left ovary. All
ratite males have an intromittent phallus without a
urethra. The retracted adult phallus lies on the floor of
the proctodeum. The female ostrich has a diminutive
phallus approximately 3 cm long which projects from a
genital mound or eminence on the floor of the
proctodeum. Among the living birds, the largest egg
belongs to the ostrich. The largest egg relative to body
weight (25%) belongs to the brown kiwi. The outer
surface of the ostrich and rhea egg is pitted, and the
emu and cassowary egg is ridged.
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Immune System
In the ostrich and other ratites, the neck of the bursa
of Fabricius has a very wide lumen, in contrast to the
narrow lumen in all the other species. Consequently, in
ratites, the proctodeum and cloacal bursa form a single
large cavity. The bursa does involute to the point of
disappearance just as in the other species, and the wide
entrance to the bursa atrophies.
RESTRAINT
Adult ratites can be fractious birds, capable of injuring
themselves or their handlers while being restrained. The
natural defense of these birds is to kick. Ostriches kick
forward at the chest level of the bird, followed by a
downward sweep of the foot. Emus and cassowaries
may kick forward, backward and somewhat laterally as
well. Rheas can kick in basically all directions when
frightened.
Capture of adult birds is accomplished with slow,
methodical approaches. Placement of a "hood" over the
head of adult ostriches generally will create a much
more tractable bird. This tends not to work for the emu
and rhea. Holding the ostrich neck and head down low
and horizontal to the ground tends to also be an
acceptable means to control an adult, while another
assistant applies upward and forward pressure to the
bird's pelvis from the rear. Restraining adult ostriches by
their wings alone is a discouraged practice due to the
potential for injury.
ANESTHESIA
Chemical restraint can be accomplished by using
injectable agents. Tiletamine-zolazepam can be
administered intravenously at 2–8 mg/kg to induce an
adult under anesthesia in less than 15 seconds.
Ketamine/diazepam can also be utilized as an
intravenous induction agent at a dose of 2–5 mg/kg
ketamine and 0.2–0.3 mg/kg diazepam. The same dose
of ketamine can also be utilized in combination with
xylazine at 0.2–0.3 mg/kg for intravenous induction as
well. Azapaerone can be administered intramuscularly
either prior to anesthetic or post induction at 1–2 mg/kg
to achieve a smoother recovery. Diazepam can be
utilized at 0.2–0.3 mg/kg intravenously also to smooth
out recovery if needed. Surgical anesthesia can be
maintained through the use of isoflurane.
Free-ranging ostriches darted with etorphine and
acepromazine showed signs of sedation within
1–3 minutes. Often, however, birds would run 300–800
meters before becoming recumbent. Only 10–20
minutes of moderate sedation was provided by this
method. Free ranging ostriches darted with a mixture of
etorphine/acepromazine and xylazine demonstrated a
significant improvement in the degree of sedation and
muscle relaxation achieved, and good sedation lasted
30 minutes. Diprenorphine hydrochloride intravenously
resulted in birds fully recovered in 1–2 minutes in both of
these trials.
Exotics — Avian
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CLINICAL PATHOLOGY
Normal hematological and biochemical values were
collected from young masai ostriches at 5 months of age
and again as adults one year later. Comparatively, the
younger birds had significantly lower concentrations of
hematocrit, hemoglobin concentrations, calcium, and
magnesium, and higher levels of total protein and
potassium than the adults.
NUTRITION
Numerous pelletized diets are currently available for
ratite species. Most of these products are quite variable
in content and quality. Range raised ostriches in Africa
are fed on alfalfa pastures and supplemented with
maize. General targets of 16–20% protein, 10% fat, and
10% fiber are believed to be good starting points for
most captive ratite species. Diets of 18% protein
produced the best weight gains in one study of ostrich
chicks that compared only the effects of varying the
dietary levels of protein.
REPRODUCTIVE TRACT DISEASE
Egg binding may present with a history of continued
reproductive activity without lay, straining, vaginal
prolapse, or no outward signs at all. Some common
etiologies of egg binding and dystocia are believed to
include malnutrition, cold weather, and lack of exercise.
Medical treatment is consistent with what is done in
other bird species, and surgical removal of bound eggs
is commonly required. Males can develop ascending
infectious of the seminiferous tublules. Prolapse of the
phallus is encountered in ostriches, and its specific
etiology is unknown. The most common cause of
infertility in the ostrich is believed to be obesity.
INFECTIOUS DISEASE
Viral Diseases
Avian influenza and Newcastle disease has been
described in ratites. Avian influenza virus has been
isolated from ostrich, rhea, and emus in the United
States, but clinical disease attributable to it has not been
recognized. Vaccination with a modified live eye drop
product has been shown to produce antibody to
Newcastle virus in ostrich and emus, and may produce
protection. PMV-1 (non-VVND) and PMV-2 have also
been isolated from ostrich chicks in the United States,
but not necessarily correlated with disease. Coronavirus
enteritis has been described in an 18-day-old ostrich
chick with clinical signs of anorexia, lethargy, weakness
and diarrhea. Poxvirus has been associated with
disease in ostriches 10–60 days old. These chicks had
small vesicles resembling mosquito bites on the eyelids
and around the external ear opening. Dry scabs
developed that covered the eyelids, but were also
present on the beak and skin of the head and neck.
Fifteen percent mortality occurred in affected birds due
to their inability to eat or see food and water. Eastern
equine encephalitis was described in a group of emus
that were exhibiting clinical signs of hemorrhagic
diarrhea and peracute mortality. The outbreak involved
juvenile and adult breeding birds ranging in age from
20 to 36 months. Morbidity was 76% and mortality was
87%. Recovered birds mounted high antibody titers.
Western equine encephalitis caused widespread disease
in emus throughout the southwestern United States in
the summer of 1992. Clinical signs included anorexia,
diarrhea, ataxia, and abnormal neck motions. A limited
number of birds progressed to lateral recumbency and
death. Vaccination with a killed three-way equine
product seemed to be protective for EEE and WEE, and
has been used to reduce or eliminate further problems in
at-risk emu flocks.
Bacterial Disease
Ratites are susceptible to numerous bacterial
pathogens, both gram positive and gram negative.
Disease processes, particularly when considering
bacterial disease, are multifactorial, involving nutritional,
environmental, managerial, and genetic factors.
Chlamydia psittaci is reported in rheas to produce
rhinitis/sinusitis, and has been isolated from ostrich
chicks as well. Mycoplasma has been isolated from the
choana as well as the reproductive tracts of ostriches,
but the clinical significance and pathogenicity of these
isolates is unknown. A beta-hemolytic spirochete is
associated with a necrotizing typhlocolitis in rheas.
Mycobacterium avium infection has been described in
emus and ostriches.
Fungal Disease
Aspergillus is reported to cause rhinitis/sinusitis and
pneumonia in ratite species. Aspergillosis is believed to
represent a ventilation related management problem.
Candidiasis is seen associated with enteritis and
malabsorption related problems in the ostrich,
particularly in young birds.
Parasitic Disease
The ostrich louse, Struhiolipeurus struthionis, is
commonly found on ostriches worldwide. Infestation is
easily diagnosed by identification of the nits glued to the
barbs along the shaft of the feathers, particularly under
the wing. Five percent carbaryl in either powder or liquid
form is reported effective. Intestinal protozoa including
Cryptosporidium, Toxoplasma, Histomonas, Giardia, and
Trichomonas have been discussed as causes of severe
and transient diarrhea in ratites. Coccidiosis is seen in
emu chicks, but has not been confirmed as clinically
significant in the ostrich. Toxoplasmosis has been
described in an adult male cassowary and an 8-monthold rhea. The cassowary presented with acute dyspnea,
and the rhea presented with anorexia and bloody
diarrhea. Both birds had high antibody titers of
Toxoplasma gondii. Other birds in the flocks were
negative for antibodies, which develop only following
infection. The wireworm Libyostrongylus douglassi is an
economically important parasite of the ostrich. Adults,
third and fourth stage larvae reside in the glandular
crypts of the proventriculus, producing a gastritis which
inhibits digestion. Diagnosis is made by identification of
the trichostrongylid-type egg in the feces. These eggs
can be confused with the harmless cecal worm,
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Codiostomum struthionis. The tracheal worms,
Syngamus trachea and Cyathostoma bronchiolis have
been reported in hemorrhagic tracheitis in the emu. The
filarid nematode, Chandlerella quiscali, is associated
with verminous encephalitis in emus. Clinical signs
include torticollis, ataxia, and abnormal gait followed by
recumbency and death. Two- to five-month-old birds
seemed to be affected, with adults and yearlings
apparently resistant. Circulating microfilaria were never
demonstrated in effected birds. Grackles are the normal
host for C. quiscali, which is transmitted by Culicoides sp
mosquitoes. Prevention may be possible by vector
control, elimination of the environmental conditions that
are conducive to transmission, and treatment to prevent
larval migration. Tissue migratory forms of the raccoon
roundworm Baylisascaris procyonis is reported as a
cause of cerebrospinal nematodiasis in the ostrich and
emu. Clinical signs noted include progressive neurologic
disease; loss of equilibrium and balance, progressive
ataxia, circling, staggering, walking backwards, and
ultimately inability to stand or walk. Environmental
contamination of the pens with raccoon feces is a
commonly incriminated source of infection. Infected
raccoons shed an average of 20,000 eggs per gram of
feces. These eggs can survive for extended periods: up
to several years in soil, cages, and enclosures
TOXICOLOGY
Numerous toxins with potential for clinical
manifestation in ratites are mentioned in the literature,
including lead, zinc, toxic plants, oil, grease, insecticides,
rodenticides, bacterial endotoxins, and enterotoxins to
name a few. Clinical signs are consistent with what has
been described in most other species. Oak poisoning
was reported in a double wattled cassowary that died
following a clinical course of severe diarrhea, anorexia,
and polydypsia after consuming leaves of the coastal
live oak (Quercus agrifolia). A diagnosis of oak poisoning
was made based on the renal lesions and the findings of
a high content of tannins in the liver and gastrointestinal
tract. Ammonia from poorly ventilated brooder
environments has been associated with conjunctivitis,
tracheitis, and pneumonia in ostrich chicks. Parsleyinduced photosensitivity has been reported in the ostrich
in which 20–30% of the diet fed was parsley.
Cantheriden, a toxin secreted by the three-striped
beetle, can be toxic to ratites. Mortality levels of 25%
were seen in a group of emus that consumed these
beetles that were attracted to a barn light.
INCUBATION
Ostrich hens lay an average of 40 to 60 eggs per
season. The egg is white in color. Egg weights range
from 1300 to 1700 grams. Baseline incubation
temperatures range from 96.8 to 97.5°F. Relative
humidity ranges between 20 and 40%, with a targeted
weight loss of 13 to 15% during the course of the 41 to
43 days of incubation.
Emu hens lay an average of 20 to 40 eggs per
season. The egg is dark green in color. Egg weights
range from 500 to 700 grams. Baseline incubation
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temperatures range from 96.9 to 98.0°F. Relative
humidity ranges between 25 and 40% to achieve a
targeted weight loss of 11 to 15% during the course of
the 50 to 57 days of incubation.
Rhea hens lay an average of 40 to 60 eggs per
season. The common rhea egg is white in color. Egg
weights range from 400 to 700 grams. Baseline
incubation temperatures range from 96.8 to 99.0°F.
Relative humidity ranges from 55 to 70% to produce a
targeted weight loss of 11 to 15% over the 36- to 41-day
incubation period.
Cassowary hens lay 8 to 10 eggs per season. The
egg is light green in color. Egg weights range from 500
to 700 grams. Baseline incubation temperatures range
from 96.8 to 98.0°F. Relative humidity ranges from 55 to
70% to produce a weight loss ranging from 11 to 15%
over the 47- to 53-day incubation period.
Vertical egg position is recommended for ostriches to
avoid or minimize malposition II (head opposite air cell).
This recommendation is suggested for all ratite eggs.
The incidence of malposition II increases from 3%
among eggs incubated vertically to 16 to 20% among
eggs incubated horizontally. Ostrich eggs are moved into
the hatcher at 40 days. Temperature is usually
decreased 0.5° Centigrade and humidity increased to 40
to 50%. Social facilitation of hatching and pipping is
strong in ratite eggs. Parents in the wild frequently assist
externally pipped chicks to hatch.
PEDIATRICS
Chicks should be maintained at decreasing
temperatures with age. Brooder substrates should be
inedible, provide good traction, and be easily cleaned.
Adequate ventilation is essential in the brooder
environment. "Wet" chicks are those chicks that did not
lose sufficient weight during the incubation process.
These chicks are weak and edematous, and may require
assistance during the hatch. Larger eggs tend to lose
less weight than smaller eggs. Excessively thick eggs,
low pore density or excessively high incubator humidity
may contribute. "Sticky" chicks are those chicks that
have lost excessive weight during incubation. The inner
shell membranes are quite dry, causing the chick to stick
to the membrane; without assistance, these chicks
frequently die. Low incubator humidity, thin egg shells, or
excessively porous eggs may contribute.
Limb deformities are common in ratite chicks. These
are usually characterized by progressive external
rotation of the tibiotarsus and tarsometatarsus. The
etiology is uncertain and is probably multifactorial.
Provision of adequate room for exercise tends to reduce
the incidence. Derotational osteotomy may correct the
deformity in select cases, but the prognosis, overall, is
poor.
Impactions of the proventriculus are more common in
the ostrich, and are decreasingly less likely in the rhea,
emu, and cassowary, respectively. Impaction is viewed
as a secondary problem—excessive ingestion of
substrate material, or representing less than optimal
emptying time or proventricular contractility. Clinical
signs of impaction include depression, small firm feces,
Exotics — Avian
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and a distended abdomen. Occasionally, lameness or
reluctance to walk will be seen. Eighty-five percent of the
impactions diagnosed occur in ostrich under 6-7 months
of age, with 10 to 12% occurring in birds six to twelve
months of age, and 3 to 5% occurring in adults.
Impactions may be partial or complete. Medical
treatment may be effective using mineral oil, psillium,
and fluids in some cases. Surgical treatment via
proventriculotomy, using both a mid-ventral as well as a
left flank approach, has been described. Slipped tendons
occur in both the ostrich and emu, and are more
common in chicks than adults. The gastrocnemius
tendon slips from the caudal aspect of the hock usually
to the lateral side. The retinacular sheath that holds the
tendon in place generally tears on the medial aspect of
the hock. Surgical repair of the retinacular sheath carries
a good prognosis as long as the injury is acute, and the
skin has not been broken open, allowing contamination
of the joint. Yolk sac retention and/or infection is a fairly
common problem in the ostrich, emu, and cassowary.
Treatment is surgical, and chicks generally do very well
once the yolk sacs have been removed. Cartilaginous
cores resembling tibial dyschondroplasia have been
seen in the long bones and vertebrae of ostrich chicks
between the ages of 1 day to 8 weeks. Soft bones and
rickets have also been described.
References available from the author upon request.
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