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.