Genetic markers for the improvement of bone strength in poultry

Bone fractures and other forms of skeletal damage are a major welfare problem in laying hens. High incidences of skeletal damage are being reported from birds over the range of husbandry systems now being introduced and it is obvious that the problem is not confined to hens in conventional battery cages. Laying hens are being selected for continuing improvements in egg output and persistency of lay and this could give rise to a progressive osteoporosis, resulting in increased bone fragility and susceptibility to fracture. Our previous work has shown that genetic factors underlie the variation in the susceptibility of individual birds to osteoporosis and bone fracture (Bishop et al., 2000), and a quantitative trait loci (QTL) of large effect, located on Chromosome 1, was characterised in a F2 population of hens divergently selected for bone strength (Dunn et al., 2007). Selection for this would help to ameliorate the propensity to osteoporosis.
To facilitate this, the loci was studied by high density genotyping of a recent generation of the white leghorn line from which the F2 were selected. Association analyses indicated a number of markers which had highly significant association to tibial breaking strength at the end of the laying period. The effect has been replicated in a subsequent generation. For the SNPs with the most consistent effects, the tibial breaking strength (N) for the alternative haplotypes in the first population was 200.4 vs 218.1 Newtons (p<0,002).
This SNP marker is also significantly associated (P=0.019) with cortical bone density (mmAl equiv/mm3). The values for each haplotype were 0.044 vs 0.050.


Overall we believe these markers have the ability to improve bone strength and improve the welfare of laying hens when applied in a breeding programme. The difference between the genotypes represents up to an 8% increase in strength and the ‘good’ allele is least frequent. Initial studies seemed to suggest the effect on egg quality was relatively small or not present.



BISHOP, S. C., FLEMING, R. H., MCCORMACK, H. A., FLOCK, D. K. & WHITEHEAD, C. C. 2000. Inheritance of bone characteristics affecting osteoporosis in laying hens. British Poultry Science, 41, 33-40.
DUNN, I. C., FLEMING, R. H., MCCORMACK, H. A., MORRICE, D., BURT, D. W., PREISINGER, R. & WHITEHEAD, C. C. 2007. A QTL for osteoporosis detected in an F-2 population derived from White Leghorn chicken lines divergently selected for bone index. Animal Genetics, 38, 45-49.