Clinical and morphological investigations on the prevalence of lameness associated with femoral head necrosis in broilers.

1. The aim was to determine the prevalence of femoral head necrosis (FHN) as a cause of lameness in broilers, and to increase knowledge of its morphological features and aetiology. The studies were carried out in two farms (A and B) in Bulgaria, on 650,000 chickens from 38 flocks. 2. Lameness in broilers varied from 3-4% up to 15% for both farms. In affected flocks, mortality due to lameness ranged between 5-6% and 10%. 3. We documented lesions in 520 broilers with signs of lameness. Samples for histopathological examination were obtained from the femur--135 from farm A and 120 from farm B. The samples originated from different batches of broilers, during different seasons of the year, and from chickens originating from parent flocks of different ages. 4. E. coli was isolated in more than 90% of the bacteriologically tested samples with FHN associated with osteomyelitis. Our large-scale field tests showed that FHN was the commonest cause of lameness in broilers.