EPIDEMIOLOGIC AND CLINICAL INVESTIGATIONS INTO BIG LIVER AND SPLEEN DISEASE OF BROILER BREEDER HENS

The epidemiological and clinical features of big liver and spleen dise ase (BLS) in flocks on two broiler breeder farms were investigated by serology and gross pathology. The most common necropsy findings on far m 1 were splenomegaly and hepatomegaly, with kidney enlargement in som e birds. In one flock (farm 1), a decline in egg production began at 4 0 weeks of age and lasted for 9 weeks. Seroconversion to BLS antigen w as first detected at 45 weeks (3.1% of birds) and increased to 72% at 50 weeks, which coincided with clinical recovery in the flock. Antigen was detected before antibody at 44 weeks and persisted at low inciden ce (< 15%). Farm egg production statistics and serology indicated that the disease affected all flocks on the farm. In three of eight flocks , seroconversion was detected in birds before peak production. The bir ds in the remaining sheds did not seroconvert or become sick until aft er peak production. On the second farm, sampling began within a flock already experiencing BLS. Clinical signs and pathology were similar to those seen in flocks on farm 1. However, the lesions that were seen i n the pancreas in 15% of birds have not been reported previously. BLS antibody was detected in 78%, and circulating antigen in 14%, of sick birds.