Abnormalities in the axial skeleton of broiler breeding fowl.

The spinal region containing caudal notarium, free thoracic vertebra (T6), and cranial synsacrum was collected from 27 male broiler breeding fowl which were about 60 weeks old when killed. In 12 birds minor abnormalities were detected on gross morphological examination, with minimal scoliotic curvature being the most frequent finding. Particular attention was paid to articulations. Radiological and histopathological examination revealed subchondral defects due to articular osteochondrosis in every spine examined. Such lesions must represent the sequelae of disturbed endochondral ossification in younger birds. Many lesions were severe, showed little evidence of repair and contained clefts and marked cartilage necrosis. Clefts were not always associated with osteochondrosis but were also observed in slightly thickened articular cartilage and that judged to be of normal thickness. In this instance clefts occurred in deep regions of articular cartilage at sites which frequently showed chondrocyte and matrix change. The latter are likely to be the primary lesions. It also seems probable that the same anatomical sites are predisposed to cell death/clefts and osteochondrosis. Clefts in adult articular cartilage, unrelated to lesions of osteochondrosis, are more likely to be progressive leading to segmental cartilage detachment and destructive cartilage thinning.