Multiple cases of osteopetrosis-like disease in young broiler flocks in Germany.

Osteopetrosis in chickens is characterized by abnormal osteoblast proliferation and is often caused by avian leukosis virus (ALV). In this study, we report a case of osteopetrosis-like disease in slow-growing broilers, which presented with lameness between days 6 and 17 after hatch. While selection rates of sick birds varied among affected flocks, the animals exhibited similar symptoms, including weakness, swollen legs, and paralysis. Post-mortem investigations primarily revealed moderate to severe symmetrical thickening of the long bones. The histology indicated a diffuse periosteal hyperplasia of the cortical area associated with a pronounced formation of mineralized bone tissue. Given the young age of the affected birds and the lack of detectable exogenous ALV, it is important to explore possible genetic factors contributing to this condition. Moreover, we cannot overlook the possibility that this condition was due to vaccines contaminated with the leukosis virus. Collaborative research is essential to identify any infectious or genetic contributors to this issue.