Focal failures of endochondral ossification in the broiler

Two types of cartilaginous lesions were observed in a flock of 400 broilers separated into four groups and fed diets containing different energy and NH4Cl contents. The lesions appeared morphologically, histologically, and etiologically different. One lesion found in the vertebrae of 10 birds consisted of focal thickenings and necrosis of growth cartilages. Affected birds were predominantly faster-growing broilers fed diets without supplemental NH4Cl. The vertebral lesions were similar to osteochondrosis as described in mammals. A second lesion consisting of cones of retained cartilage was present in various long bones of 27.5% of all birds examined. The peak incidence of these dyschondroplastic lesions occurred in the slowest-growing group of 4-week-old birds fed diets containing 3% NH4Cl: 70% of these birds had dyschondroplasia. No positive correlation was found between the incidence of the vertebral lesions of osteochondrosis and the appendicular lesions of dyschondroplasia.