Pathology of the skeleton and tendons of broiler chickens reared to roaster weights. I. Crippled chickens.

The incidence of cripples among broiler chickens kept until 74 days of age was greatest in chickens fed ad libitum and kept in batteries. The incidence was lower in chickens kept in floor pens and was reduced by feed restriction. Crippling was due to long-bone distortion, rupture of the gastrocnemius tendon, and spondylolisthesis. Long-bone distortion was the most common defect and could be divided into valgus and varus deformation. The former was more important in chickens less than 7 weeks of age, and the latter was more important in older chickens. Tibial dyschondroplasia was found in some chickens with long-bone distortion, and the possible significance of this abnormal cartilage as a cause of long-bone distortion is discussed.