MEDULLARY BONE AND HUMERAL BREAKING STRENGTH IN LAYING HENS

To test the hypothesis that large amounts of medullary bone in the hum eral diaphysis may increase breaking strength, various parameters of b one quality and quantity were examined in two large flocks of hens nea r end of lay. We conclude that the amount of medullary bone in the hum erus of hens during the laying period influences bone strength. This m edullary bone may not have any intrinsic strength, but may act by cont ributing to the fracture resistance of the surrounding cortical bone. Using a quantitative, low dose, radiographic technique, we can predict , from early in the laying period, those birds which will develop larg e amounts of medullary bone in their humeri by the end of the laying p eriod. The formation of medullary bone in the humeral diaphysis is not at the expense of the surrounding radiographed cortical bone.