Photographic encyclopaedia of Australian poultry diseases compiled by Dr Balkar Bains

View the complete set of images here.


Ascites, or water-belly is a condition seen in broiler chickens most commonly from two weeks of age onwards. The accumulation of fluid in the body cavity is a consequence of inadequate volume of blood passing through the lungs and blood volume accumulates in the blood vessels in the body cavity. The excessive blood volume distends the blood vessels and the fluid leaks out in the body cavity.

Distended abdomen filled with fluid

Accumulated fluid, congestion of liver and skeletal muscles

Avian encephalomyelitis

Avian Encephalomyelitis also known as Epidemic Tremors is caused by a viral infection in susceptible chickens. Clinical signs include falling over, lying on their side and fine tremors of the head and neck. Morbidity in a flock may vary and the cause of death is usually from trampling, starvation and dehydration. Following an A.E. outbreak some chickens may develop  cataracts and blindness.

The embryo inoculation technique has been used for diagnostic purposes and for virus isolation. The characteristic embryo lesions are the atrophy of the skeletal muscles and the death of the embryo.

Atrophy of the skeletal muscles and death of the embryo

Development of cataracts and blindness

Chicks with AE

Bent tibia

Bent legs or twisted tibias are seen in broiler chickens probably related to metabolic inadequacy or inadequate calcification. The leg bones in the affected chickens are soft and easily bent under pressure and sometimes twist and cause partial dislocation of the joints of the legs. The affected chickens experience difficulty in walking and in extreme cases are unable to move about.

Bent Tibia / Twisted Leg – Showing normal tibia in the centre for comparison.

Biotin deficiency

Biotin is required for many functions including gluconeogenesis and protein synthesis as well as being essential for life, growth and maintenance of epidermal tissues. Biotin deficiency can cause the bottom of the feet (foot pads) to become rough and calloused and may even contain fissures which may also become infected, spreading the infection to toes. Severity of the lesions depends upon the duration of the deficiency and any concurrent infection.

Unthriftiness, retarded growth, brittle feathers and scaly, dry skin in a turkey poult.

Calloused and infected foot pad and toes.

Perosis or slipped tendon from the hock joint in a turkey poult 1

Perosis or slipped tendon from the hock joint of a turkey poult 2

Damage to foot pad and toes.

Fowl cholera

Fowl Cholera is an infectious disease that may occur as both acute septicaemic and chromic forms. The infection tends to persist in the poultry farm environment probably by surviving in other resident host vermin populations. In the chronic form, as shown in the picture, the apparent swelling of the wattles and the yellow discharge from the sinuses is indicative of Fowl Cholera.

Fowl Cholera – Chronic Form.

Choline deficiency

The deficiency of Choline in young chickens may result in flattening of the tibiotarsal joint due to rotation of the metatarsus and finally perosis due to deformed cartilage as shown in the picture below.

Choline deficiency

Clostridia perfringens

Clostridia perfringens is endemic in the poultry farming environment and the resistant stage of clostridium outside the host chicken ensures its survival. In the chicken the organism grows on the feed the chicken eats and its proliferation results in the production of a specific toxin that causes toxaemia, depression, external haemorrhages and death.

Clostridia perfringens proliferates in the intestinal environment and toxins thus produced cause damage to the mucosa. In acute cases onset of the condition is rapid and morbidity and mortality can be  high. Post-mortem examination reveals necrotic foci and pinpoint haemorrhages visible from the serosal surface. The lesions may also suggest the possibility of  Eimeria necatrix infection.

Post mortem examination revealing mucoid enteritis and haemorrhages evident from the presence of blood in the intestinal content. The lesions may sometimes be confused with Eimeria necatrix.

Post mortem examination revealing very fragile and thin intestine distended with gas. The watery content is a greenish colour and has a characteristic smell.

Post mortem examination revealing very fragile and thin intestine and the lining of which is easily peeled away. The intestinal contents made up of smelly greenish debris typical of necrotic enteritis. Concurrent coccidiosis may also influence the severity of the disease.

This congested and dark coloured liver was seen in a chicken which had died of Clostridia perfingens toxaemia.

Haemorrhages of the wing and body 1

Haemorrhages of the wing and body 2

Haemorrhages of the wing and body 3

Haemorrhages of the wing and body 4

Very fragile and thin intestine and the lining of which is easily peeled away.

Chicken showing depression  and external haemorrhaging – See left wing.


Coccidia (Coccidiasina) is a subclass of microscopic, spore-forming, single-celled obligate intracellular parasites (meaning that they must live and reproduce within an animal cell) belonging to the apicomplexan class Conoidasida.

Infection with these parasites is known as coccidiosis.

Coccidiosis causes considerable economic loss in the poultry industry. Chickens are susceptible to at least 11 species of coccidia.

The complex life cycles of the coccidia strains virtually ensures its survival in the poultry environment. In the prolific reproductive state that takes place in part of the intestines

The most common species are Eimeria tenella, which causes the cecal or bloody type of coccidiosis, E. necatrix, which causes bloody intestinal coccidiosis, and E. acervulina and E. maxima, which cause chronic intestinal coccidiosis.

Eimeria oocysts are shed in the intestines and passed in the droppings to sporulate in the poultry house litter. Both the size and the shape of the oocyst are used as tools to identify and type the eimeria species.

Coccidia oocysts 1

Coccidia oocysts 2

Coccidia acervulina 1

Coccidia acervulina 2

Coccidia acervulina 3

Coccidia brunetti

Coccidia maxima 1

Coccidia maxima 2

Coccidia necatrix 1

Coccidia necatrix 2

Coccidia tenella 1

Coccidia tenella 2

Coccidia tenella 3

Coccidia tenella 4

Coccidiosis in a chicken


Infectious Coryza or Coryza as it is generally known is caused by a bacteria, Haenophilus, infecting intraorbital sinuses and conjunctiva.

The facial swelling,  as seen in the picture, is due to either clear or purulent material that may discharge from the nostrils. In chronic cases the yellowish, cheesy material is present in the intraorbital sinuses. Infection tends to become chronic in the flock.

Infectious Coryza

Chronic respiratory disease (CRD) – mycoplasmosis

In the early stages Mycoplasma gallisepticum infection causes watery to purulent eye and nasal discharge and inflammation which can cause the eye to appear misshapen as seen in Image 1.

The infection spreads to the sinuses and the upper respiratory tract leading to coughing and difficulty in breathing.See Image 2.

The secondary infection of E. coli causes varying degrees of peritonitis and death. Collibacillosis is caused by coliform bacteria which are abundant in the ;poultry environment. The bacteria gains its entrance to the visceral organs through damaged intestinal lining, damaged blood vessels or via the respiratory tract by inhaling contaminated dust particles. Under conditions where infection becomes chronic there is generalised peritonitis and deposits of fibrin as a result of immune response as seen in Image 3 as white deposits on the liver.

Image 1

Image 2

Image 3

Dilated proventriculus

Dilated proventiculus is thought to be caused by ionophore toxicity especially when there are no visible lesions or inflammation readily observable.

A normal proventriculus can be seen in the centre of Image 1 and the dilated specimens are on either side.

Exudative diathesis – selenium deficiency

Clinical signs of Selenium deficiency are known as exudative diathesis, characterised by the obviously pendulous appearance of the neck which on palpation feels soft.

This is the consequence of oxidation of lipid layers of cell membranes lining the capillary walls. The resulting structural disorganisation causes increased permeability and thus permits fluid to exude into subcutaneous tissues, most commonly seen as a soft swelling of the neck.


Tibial dyschondroplasia & femoral head necrosis

Tibial dyschondroplasia is a condition where the cartilage below the growth plate continues to persist instead of calcifying. The condition is seen in long bones and particularly evident in faster growing chickens. Due to lack of adequate calcification the bone at its extremities remains soft and often bends under pressure or heavy body weight.

Femoral Head Necrosis is the result  of poor calcification of the long bones in fast-growing breeds of broilers.

Image 1 is of an X-ray that shows the difference in calcification between a normal bone on the right and an affected bone on the left.

Image 2 shows the persistence of cartilage as a white plug just below the growth plate in the tibia of a broiler chicken. The bone is not only bent but can easily fracture causing severe lameness in affected chickens.

Image 3 –  The femoral head is very soft and easily cut with scissors and this area of the femur is susceptible to bacterial infection.


Favus is chronic infection of the comb and face caused by Trichophyton megnini.

Signs appear as white spots on the comb, eventually covering the entire face, giving it the appearance of being sprinkled with flour and it may even form a crust over a period of time.


Gizzard erosion

Gizzard erosion is characterised by varying degrees of ulceration on lining of the gizzard which may render it inefficient in its important function of grinding food before it passes into the intestine.

There are a number of well-known causes which may cause gizzard erosion e.g. viral infections, mycotoxins etc