Normal and pathologic skeletal development in broiler and leghorn chickens. A comparative investigation.

Skeletal development of broilers of two lines of the Hybro Compact strain was compared to the skeletal development of leghorns. Environment, management, and feeds were identical for comparable groups of broilers and leghorns. Half of the broilers (representing both lines) and half of the leghorns were given a high energy feed, while the other half of the birds of both breeds were given a low energy feed. No great difference in feed conversion between broilers and leghorns was found. The broilers consumed more feed and increased their body weight and volume of the tibia almost twice as fast as the leghorns. The difference in longitudinal growth of the tibia of the birds of the two breeds was much less evident. Locomotor disturbances (leg weakness) were common in the broilers, and in the majority of the cases the problems were caused by skeletal deformities. The leghorns were almost completely free of skeletal deformities and had no locomotor disturbances. Likewise, dyschondroplasia was not found in the leghorns, while it was common in the broilers. Most of the skeletal deformities in the broilers were explained as the result of mechanic-traumatic factors, acting on a rapidly remodeling skeleton, apparently of insufficient strength for the heavy body weight. Dyschondroplasia, on the other hand, was considered to be caused by a generalized factor governing growth. Basic histologic differences between broilers and leghorns already at an age of 7 days supported this theory. It was concluded that both leg deformities and dyschondroplasia in the broiler are man made problems, caused by genetic selection for characteristics of economic importance, without enough consideration to function and health of the animals.