Disturbed endochondral ossification in the axial skeleton of young broiler fowls.

Physeal lesions have been studied in thoracic vertebrae (T3, T4 and T5) of 51 broiler fowls between 28 and 53 days old. Vascular perfusion studies performed on 10 birds confirmed that the cartilaginous epiphyses of T3, T4 and T5 were essentially avascular and thus differ from those of the major long bones. Findings confirm the observation that a number of morphologically distinct lesions of osteochondrosis occur in broiler fowls and that, when physeal clefts can be implicated in their aetiology, the term "osteochondrosis" is inappropriate. Although the location of clefts often differs in long bone and vertebral physes, when metaphyseal vessels are disrupted, the end-result on endochondral ossification is the same in both the axial and appendicular skeleton. Other lesions were observed both independently and in association with osteochondrosis. Such lesions include necrotic seams devoid of haemorrhage, acellular foci and chondrolysis, all of which were most frequently observed in the same vertebral end-plates. Because osteochondrosis was also most common in the same vertebral end-plates, a common aetiology is suggested. Surface regressive changes were common in the articular cartilage of T3, T4 and T5, and it is noteworthy that such changes, although common in older birds, are present in birds so young.