Diseases of Game Birds
Part 3 - Early Rearing
John Dalton BVMS MRCVS
Fig 2. Aspergillus. Advanced air sacculitis
Aspergillosis
Fig 3. Aspergillus associated kerato-conjunctivitis.
Section through eye
Avian encephalomyelitis (Epidemic Tremors)
Cause: Avian encephalomyelitis virus. A picorna virus.
Fig 1. Aspergillus. Cloudiness in air sacs
Cause: Any disease caused by a member of the
Aspergillus fungal family is identified as Aspergillosis. It
causes three primary disease patterns which affect
variously the respiratory tract, the eye and the brain.
Signs: That seen in game birds most commonly is
seen as pneumonia or sacculitis. (Figs 1 and 2) (As
might be expected presenting signs are laboured
breathing which in the terminal stages is gasping, with
the beak open and neck stretched in an attempt to get
sufficient air into the lungs. Also occasionally eye
lesions occur (Fig 3 ).
Signs: Although thankfully not too common in game
birds in the UK, it does have devastating
consequences if introduced to a flock. It is most often
seen in very young birds. Presenting signs area
characteristic trembling (or tremor). (Fig 4) Affected
birds are very obviously dull and depressed. The rate
of infection (morbidity) is very high (40-60%) and
rapidly spreads from group to group on the same unit
(especially if there are varying age groups there, as is
often the case). Mortality may be as high as 50%.
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usually due to pericarditis or perihepatitis, a white
covering around the heart or liver. The liver is black
and smelly and the spleen enlarged. A blood smear,
including those taken from bone marrow, will show
several rod shaped bacteria.
Fig 4. Avian encephalomyelitis. Trembling makes
sharp focus impossible
E. coli is often found as a secondary pathogen with
other
conditions
such
as
coccidiosis,
mycoplasmosis or Histomonas. The damage
caused by the primary pathogens make possible
the colonisation by E. coli strains that normally
would not be able to cause any problems. The
secondary damage done by E. coli will often result
in death.
Spread. Infection can be egg transmitted and so
the disease can unknowingly be bought-in with
chicks. Virus is shed in high quantity in the
droppings and may remain infective for a long time.
Action: Because of the highly infectious nature
slaughter of affected birds may be considered as a
control measure. Vaccine is available for breeder
flocks.
Chilling
When, for any reason, the heat source fails in
young birds they will huddle and eventually heap to
try to get warm. This usually leads to death by
smothering (see Smothering below).
Colibacillosis/coli septicaemia
Cause. Colibacillosis is usually caused by
Escherichia coli but can also be caused by other
coliform bacteria. There are many strains of E. coli
normally living in the intestinal contents without
causing any trouble. Under certain conditions
however, especially when the bird is stressed or
suffering from another illness, particular strains may
spread to other organs causing disease and
eventually killing the bird.
Birds may be affected at any age, but it is mainly
seen in (very) young or immuno-suppressed birds.
Spread. The infection is not contagious. Birds can
only pick it up from the environment.
Colibacillosis is found world wide and can occur
anywhere and any time birds are living in damp dirty
litter. Day olds can get infected in the hatchery
when eggs are contaminated with droppings in the
laying pens.
Signs. Septicaemia, or blood poisoning, is the most
common acute form. (Fig 5) Later losses are
Fig 5. Colisepticaemia. Haemorrhages on surface of
intestines. Congested blood vessels in major organs
Treatment. Treatment consists of antibiotic therapy.
Preferably the organism is isolated, typed and a
sensitivity test carried out to determine the right
antibiotic.
Control. Antibiotic treatment can not cover up bad
hygiene! Sanitation of the environment, drinkers
and feeders is more important. Restrict the contact
of birds with droppings. To prevent problems
occurring thoroughly clean and disinfect brooder
houses in between hatches. Keep litter, feeders and
drinkers as clean as possible. Dead birds or
unhatched eggs should be removed and incinerated
as soon as possible, unless they are going to be
brought in for post mortem.
Don't forget cleanliness in egg gathering, cleaning,
storing, incubating and hatching.
Mycoplasmosis (Bulgy eye)
Cause. Mycoplasmosis has been recognised in
pheasants and partridges since the 1950`s. The
commonest organism found in our species is
Mycoplasma gallisepticum. There is a whole host of
related bacteria, but their ability to cause disease is
not always known.
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Signs. Clinical disease is most often seen in adult
birds although all ages may be affected. Mortality in
chicks 7 to 14 days old can be devastating.
Respiratory symptoms and sinusitis ("bulgy eye").
Joint infections may be seen as well (see below).
Clinical signs develop slowly within the flock but
stress, poor ventilation, and a cold and damp
environment will make things worse. Signs include
ocular discharge, swollen sinuses, (Fig 6) sneezing,
mouth breathing and a reduced growth rate. Egg
production is also affected with reduced production
and hatchability and pale coloured eggs with thin
shells. Joint infections are seen mainly in the leg
joints (mainly the hocks). These are swollen and the
joint space often contains orange coloured liquid,
with the lining of the space thickened (synovitis). It
is thought that Mycoplasma synoviae is involved in
this, but this has yet to be proved.
Control. Try to keep a closed flock, but when you
have to buy-in try to buy birds from reputable
sources. Bought-in birds must be quarantined
before being added to the resident flock. Never
forget the importance of good management
(especially drinkers) and biosecurity!!
Vaccine. There is a live commercial poultry vaccine
available for spray vaccination in poultry in the UK.
It may give some protection in gamebirds. Care
must be taken when giving these vaccines. It is vital
to follow the instructions closely!
In mainland Europe there is a killed injectable
vaccine that has been used in the UK as well. Once
again it is not clear how much the protection is
given to gamebirds when it is used. There are also
risks to anyone using the vaccine if they
accidentally self-inject.
Navel ill
See under Yolk sac infection
Newcastle disease
Significance. Although you should not see this in
birds of this age, it has to be described here
because of the potential severe consequences,
both in mortality because of the disease, and
possible compulsory slaughter of affected flocks if it
is confirmed.
Fig 6. Bulgy Eye. These chicks are showing typical
swelling below the eye
Spread. Bird to bird close contact, via air droplets,
infected
litter
and
equipment
(horizontal
transmission), and from hen to chick via the egg
(vertical transmission). Recovered birds will remain
carriers and shedders; therefore, once your flock is
infected it will remain infected.
Treatment. Treatment of clinically diseased animals
should only be carried out to salvage the shoot of
that year. Do not keep any recovered animals for
breeding, as they will most likely be carriers! The
bacteria are sensitive to several antibiotics and are
easily destroyed by sanitisers, disinfectants and
direct sunlight. Control will mainly be aimed at
breeders. When catching up birds, cull animals that
show any signs of disease. When Mycoplasma is
present on the shoot it is possible to treat the birds
with antibiotics during stressful periods, please
discuss this with your vet.
Cause. Newcastle disease is a notifiable disease
caused by a Paramyxovirus Type 1. It is spread
worldwide and can cause considerable losses. Over
250 bird species are susceptible!
The virus was first isolated in 1926 in the Far East,
thereafter it was found in Newcastle upon Tyne
(hence the name).
Signs. The disease was first reported in pheasants
in the UK in 1963. The severity of the disease
depends on the virus strain, the species affected,
the immune status, condition and age of the bird
and whether the birds are suffering from concurrent
diseases.
The respiratory system, the intestinal system and
the neurological system can be affected.
Symptoms include respiratory disease, diarrhoea,
nervous signs, swelling of the neck and face and
sudden death. Hens may stop laying or produce
misshapen eggs. In severe outbreaks mortality can
reach 90%! In young birds, nervous signs with
sudden high mortality are most likely to be seen.
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Post mortem. There are no specific diagnostic
lesions. There may be haemorrhages in the
intestinal
mucosa,
cloaca,
pancreas
and
proventriculus. There can also be congestion in the
lungs, liver, spleen, kidney and air sacs. The liver
may be discoloured and there may be an enteritis
and weight loss.
Diagnosis by blood samples or virus isolation from
the cloaca, trachea or brain.
Spread. Can be spread by direct contact with
excretions, especially droppings, from infected
birds. Infection may occur orally or by inhalation.
Cause; Calcium or Vitamin D deficiency. Generally
seen in birds slightly older than 10 days, but in
severe cases may be younger.
Signs. Birds usually present with lameness and
ability to walk or stand. Limbs may be bent.
It is because is usually dietary that it is seen at 2 to
4 weeks old. If the egg itself is very thin shelled,
resorption of calcium from the shell to the chick in
late stage incubation is poor and they may
theoretically be born affected.
Spread. The disease can be spread by any one of
the following:
Movement of live birds
Airborne spread
Contaminated feed or water
Fig 7. Rickets in young pheasant. "Rickety Rosary".
Internal
Non avian animals
Vaccines
Movement of poultry products
Movement of people, vehicles and equipment.
Newcastle Disease is notifiable but statutory action
only needs to be taken for virulent strains. The last
virulent outbreak in England was in 2005 (in
pheasants imported from France).
Post mortem signs: There is often swelling along
the line of the junction of the bony section of the rib
with the cartilage, leading to what is classically
described as a "Rickety Rosary". (Fig 7) As you run
your fingers along the line there is a distinct knobbly
feeling. The long bones of the leg may be bent,
rubbery or even have spontaneous fractures. (Fig
8)
In case of an outbreak, there will be a ban on the
export of live birds, eggs and poultry products. The
length of the ban and the effect on the poultry and
allied industry will depend on the extent of the
spread and the time taken to eradicate it.
Treatment/Control, There is no treatment for the
disease. Control will depend on good biosecurity
measures combined with vaccination and / or
eradication. In most countries eradication by
slaughter has become the main policy, however,
one needs to consider the economical and political
pressures in most European countries.
Vaccination will prevent deaths, clinical signs and
egg production problems but will not prevent birds
getting infected. Infected vaccinated birds will still
excrete the virus but in relatively small amounts.
Therefore many countries will not accept vaccinated
birds.
Ricketts
Fig 8. Rickets in young pheasants. Fracture of femur
and "Rickety Rosary". External
Rotavirus enteritis
Cause. Rotavirus. Is seen more and more
frequently. It affects poults from a few days old, right
up to 7 or 8 weeks (or more) of age.
Signs vary with the age of the bird affected. In the
first week of life moist droppings, lethargy and
sometimes a string of sticky droppings trailing
behind the bird may be seen. Mortality is variable,
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but can be as high as 80%! A high proportion may
look pretty poorly. Sometimes you may find a heap
of dead birds first thing in the morning. There is
often a characteristic smell in the house or shed,
associated with the very liquid droppings. Food
consumption usually plummets, but birds will drink.
You may find dead birds lying in the drinkers. The
bedding material is wet in more places than just
around the drinkers or feeders. 2 to 3 week old
birds suffer lower mortality, but fail to thrive. They
are often wet around the vent, huddling and eating
less.
Once again large numbers can be affected. In the
5-week plus bird the signs are often complicated by
the presence of one of other conditions such as
Hexamita (Spironucleus), Trichomonas, Blastocystis
and Coccidiosis, or a mixture of any of these. The
droppings are characteristically pale to mustard
yellow. Mortality in this age is low, but many
affected birds never truly recover, going on to
become the razor keeled rejects so often seen.
Diagnosis is based on post mortem examination of
affected dying birds and some already dead. Post
mortem changes are usually seen in the blind gut
(caecum), which is distended and contains yellow
frothy or slightly pasty liquid. (Figs 9 a & b) It is not
possible to differentiate between these gross signs
and those of acute early coccidiosis without
microscopic examination of the gut contents.
CORRECT AND ACCURATE DIAGNOSIS IS
VITAL. Ultimate diagnosis depends on identification
of the virus by electron microscopy. This is a
disease most commonly associated with poor egg
hygiene, incubator technique and hatchery
management. Infection is also transmitted from the
hen through the egg to the chick.
Figs 9a (above) &9b (below). Rotavirus infection.
Distension of blind gut (caecum) with frothy yellow
liquid
Treatment. There are no specific medicines
available that act directly on the virus. Treatment of
affected birds relies on: Electrolytes, antibiotic
cover, vitamins, extra heat, disinfection and
protection of other birds. Medicated water must be
supplied fresh at least twice per day. Drinkers must
be disinfected at least once a day. Wet patches and
popholes should be treated with disinfectants or
desiccants. Boots must be disinfected before and
after seeing to the birds. Separate overalls should
be worn in affected houses. Dead birds and
contaminated bedding and chick boxes must be
burnt. This is a highly infectious disease; spread by
humans is as common as by birds.
Salmonella enteritis
Figs 10a (above) &10b(below). Salmonella. Pheasant
Caeca with hard cores
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Cause. Although regarded as many as "normal",
starve-out is in fact a "disease" which is triggered by
the artificial rearing of chicks. The broody hen
encourages her young to eat by demonstrating
scratching and turning up food for them. In the
brooder hut, although the food is likely to be
plentiful, the young chick may fail to eat and hence
"starve out" for a number of reasons. These include
being too hot, too cold, too crowded, dehydration,
poor access to feeders, unpalatable feed (maybe
when it has been over-heated, stale or incorrectly
stored) as well as suffering from other diseases.
Cause. Various members of the Salmonella group
of bacteria.
Although this can cause serious disease in young
birds, often with high mortality, it is also a Zoonosis
and must be reported to Defra if it is diagnosed.
Signs. As with so many diseases of very young
birds often all you see is "sickly" looking birds.
Post-mortem signs. Sometimes "classical" white
cores are seen in the caeca. (Figs 10 a & b)
However, such cores can also be seen in
coccidiosis, so absolute diagnosis in the laboratory
is essential, not only to get the correct treatment,
but to make sure that the Public Health risk is
minimized.
Signs. The chick will survive for several days
without eating; relying of the nutrients remaining in
the yolk sac to keep it going. As the yolk sac is
resorbed the food value drops and unless replaced
by true food, the chick's blood glucose level falls.
This in turn leads to reduced activity and appetite,
setting it only the downward spiral to death.
"Starve-out" peaks at 3 to 4 days old. If mortality
continues beyond this time, an urgent investigation
into other causes must be made.
Chicks that have died of starvation typically have an
empty crop and gizzard and a distended
gall-bladder. (Fig 12)
Smothering
Although not an infectious disease this is a common
cause of mortality in young poults. There are
basically two causes. One is huddling because of
chilling when the background temperature is too
low. The other is when birds are panicked into a
heap. This can happen when there are storms or
predators get into or near the brooder hut or grass
run.(Fig 11)
Fig 12. Starve-out. Distended gall bladder
Fig 11. Smothering. Close up of heart. Often
elongated, or slightly "pointed" in smothered birds.
Starve-out
Fig 13. Yolk sac infection.
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Yolk sac infection / Navel ill
Cause. Bacterial infection either of the navel either
during incubation or soon after hatching. As the
chick develops in the egg, the yolk lies outside the
body cavity, connected to the intestines of the bird
by the umbilical cord. The embryo will use about
80% of the yolk sac contents during incubation. The
remainder of the yolk sac gets withdrawn into the
body cavity 2 to 3 days before hatching. The rest of
the yolk will be used up in the first 5 days of life by
which time the chick should be able to eat and drink
the provided water and food. The yolk sac does not
only provide an excellent source of food for the
embryo. It is also very attractive for invading
bacteria such as E. coli, Staphylococcus, Bacillus
cereus, Enterococcus, Klebsiella, Pseudomonas,
Clostridium and Proteus. Infection is contracted
from the environment and is not usually spread from
bird to bird, but infected birds may contaminate
others around the time of hatching.
Birds can get infected before eggs are set, during
incubation or during transport or early brooding.
The egg shell is full of pores, but is protected by a
cuticle. When this cuticle is damaged or removed
bacteria can penetrate the egg through the pores.
Active scrubbing of eggs to clean them will do just
this. Bacteria can also penetrate if the eggs are laid
in a dirty environment, especially when left for a
while, as bacteria will be drawn in to the egg as it
cools down. If eggs are washed in a cold solution
this process is accelerated.
produced by the bacteria or from septicaemia. Yolk
sac infections are always caused by bacteria.
Isolation and identification is needed to determine
the source of infection and probability of an ongoing
problem.
Treatment. There is no treatment as most chicks
will die within the first few days. One can only give
supportive therapy such as electrolytes and
vitamins.
Action. When mortality exceeds 3% an
investigation should be carried out into egg shell
quality, egg handling and sanitation. Incubation /
hatching procedures, machine sanitation and other
possible contributing factors such as ventilation,
personnel etc
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During incubation dirty eggs or contaminated air are
responsible for infection. Too high or too low
humidity will increase problems. If the hatching is
slowed down and the navel is slow to heal there is a
greater chance of bacteria invading via the navel.
Handling eggs / chicks with contaminated hands
also increases the infection rate.
Signs. Chicks may be healthy when leaving the
hatchery, but infection can enter via the intestines if
the birds are stressed during transport or early
brooding, also chicks can get infected via unhealed
navels. When birds get infected early in life the
embryo may die in the shell or shortly after
hatching. With later infections birds usually start off
normally but will become depressed and die a few
days later. A large yolk sac will be found with very
fluid yolk. (Fig 13) Often there is peritonitis with a
very rotten smell. The chicks die from the toxins
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