Pathology of the skeleton and tendons of broiler chickens reared to roaster weights. II. Normal chickens.

Broiler chickens were raised to 74 days of age under different feeding and housing regimens. Conformation, growth plates and tendon strength were studied in clinically normal chickens of various ages. A change with age from slight valgus deviation of the metatarsal bones to varus deviation was recorded. Separation of the proximal femoral epiphysis from the femur on disarticulation of the coxofemoral joint was a common post-mortem artifact. It was more common in chickens on full feed than in chickens fed a restricted amount of feed. Two distinct growth-plate abnormalities were recognized. Dyschondroplasia was most common in the proximal tibiotarsus and was almost completely absent in chickens fed a restricted amount of feed. Eosinophilic streaks were found in growth plates of the proximal femur and the thoracic vertebral bodies. The incidence of these streaks was not affected by feed restriction. It is suggested that these streaks represent microscopic tears in growth plates exposed to shear forces and that they may be similar to osteochondrosis in mammals. The tensile strength of the flexor digitus perforatus and perforans tendon to the third digit increased with age. It was not affected by housing or feeding regimen, but the ratio of tensile strength over body weight was less in chickens fed ad libitum than in those fed a restricted amount of feed.