Studies on the pathogenesis of tibial dyschondroplasia in chickens. II. Growth rate of long bones.

The growth rate of the tibiotarsus, tarsometatarsus, and humerus was studied in two strains of chickens selected for a high and low incidence of tibial dyschondroplasia. The proximal growth plates grew more rapidly than the distal growth plates. The proximal growth plate of the tibiotarsus grew fastest, while those of the tarsometatarsus and humerus had growth rates that were respectively 4 and 33% slower. The bones averaged slightly faster growth in the high-incidence strain than in the low-incidence strain. A slowed growth decreased the incidence of tibial dyschondroplasia. However, lack of correlation between growth rate and the development of tibial dyschondroplasia in individual chickens suggested that growth rate may be no more than a contributing factor.