Inheritance of bone characteristics affecting osteoporosis in laying hens

1. Heritabilities of a range of morphometric, radiological and strength cha racteristics were measured in the bones of end-of-lay hens. 2. Tibial strength (TSTR), humeral strength (HSTR) and keel radiographic de nsity (KRD) were moderately to strongly inherited and were combined in a Bo ne Index which was used as a basis for selection. Data are available on 6 g enerations/cohorts of hens (n=1306), the last 3 of which are the progeny of divergently selected birds. 3. All bone characteristics used in the Bone Index responded rapidly to div ergent selection and were strongly correlated with each other. In the last generation, the lines differed by 25% for TSTR, 13% for HSTR and 19% for KR D. The heritability of the index was 0.40. 4. There were no apparent genotype by environment interactions between bird s housed at 2 different locations. 5. The incidence of bone fractures was significantly decreased in the line selected for high bone strength compared to the line selected for low bone strength. Humerus fracture incidence differed by a factor of 6 between the lines in the last generation. There was a strong quadratic relationship bet ween tibia strength and overall fracture incidence (r(2)=0.92, P<0.01). 6. The results imply that selection for enhanced bone strength can be used as a long-term strategy for alleviating the problems of osteoporosis in lay ing hens.