Commercial Layers and Layer Breeders

Marek's disease

The visceral form of Marek's disease was confirmed in a sequential submission of 38-week-old free-range layers with protracted mortality and a slight drop in egg production. Creamy white, nodular to diffuse organ enlargement observed in the spleen, liver and heart was confirmed histopathologically as pleomorphic lymphomas.

Broilers and Broiler Breeders

Enterococcus hirae

Increased mortality associated with neurological signs, including torticollis, in six-day-old chicks was attributed to Enterococcus hirae septicaemia. Post mortem findings included swollen livers and spleens. Histopathological examination of brains revealed lesions of encephalomalacia in the cerebrum midbrain, but not in the cerebellum, consistent with E. hirae associated encephalomalacia. Routine bacteriological cultures of livers and spleens yielded heavy pure growths of Enterococcus species with biochemical features consistent with E. hirae.

In another case, vegetative endocarditis due to E. hirae and septic arthritis due to Staphylococcus aureus were diagnosed in a flock of 20-day-old broilers with suspected 'sudden death syndrome'. Post mortem examination revealed distended right heart ventricles with nodular proliferations on the atrio-ventricular valve in one carcass and purulent exudate in the hip joint of another carcass.

Marek's disease

Chronic typhlitis associated with histomonosis (Blackhead), proventricular lymphomas and severe immune-suppression were diagnosed in a batch of 58-day-old free range organic broilers from a multi-aged farm with a history of poor growth and unevenness. Post mortem examination revealed stunted birds, one of which showed markedly thickened and chronically inflamed caecae with a ruptured wall leading to peritonitis and enlargement of the liver with irregular foci of necrosis.

In two other carcasses, the main finding consisted of extensive necrosis of the proventricular mucosa. Histological examination confirmed a severe immune-suppression in most carcasses characterised by diffuse bursal atrophy, liver and caecal lesions consistent with histomonosis and a pleomorphic lymphoma in proventricular samples consistent with Marek's disease. A revision of vaccination protocol was recommended.

Infectious bronchitis (IB)

Two strains of infectious bronchitis virus (IBV) were identified in a submission of oropharyngeal swabs from 32-day-old broilers. Poor growth rate and litter conditions with some feed rejection were described in the flock. One of the IB viruses proved to be a vaccine strain and the other gave a 97.14 per cent similarity to the European QX IBV strain.

Botulism in Cattle

Leahurst investigated outbreaks of suspected bovine botulism on two neighbouring farms.

On the first, broiler chickens were reared, as well as calves for a dairy herd, which was housed elsewhere. Immediately following depopulation of the broiler shed, five-month-old calves in a shed accessed from the same yard developed recumbency and paresis/ paralysis of hind legs, dying within 24 hours of onset of signs, despite treatment. Six died over five days. Six days after deaths began on the affected farm, broiler litter which had been stacked for months on a field between the broiler shed and the neighbouring farm was spread and ploughed in.

Two days later, in-calf heifers on the neighbour's premises, a heifer-rearing unit, were moved to a yard bordering this field where they could be handled for vaccinating. The following day, a heifer was recumbent and unable to rise. She died later that day and over the next week, five more heifers died similarly.

Clinical signs included weakness and knuckling on the front legs, hyper-salivation, hypothermia and sweating prior to death, all of which were consistent with a diagnosis of botulism. A risk assessment to protect the food chain was carried out.

Ovine Botulism

Penrith diagnosed botulism on three separate farms none of which were linked. They remarked that outbreaks at this time of year may initially be mistaken for cases of hypocalcaemia. Some clinical cases were found dead, some with flaccid paralysis and recumbency, some with stunted or altered gait. All three outbreaks were associated with broiler litter which had been stacked near the affected sheep. No threat to the food chain was identified by official risk assessments.

Further Reading

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Further Reading

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