BoneQTL: Selectable markers for bone strength for the poultry industry

Bone fractures and other forms of skeletal damage are a major welfare problem in laying hens. Osteoporosis is a major contributory factor in the problem. It results in a progressive loss of structural bone over the egg laying period, rendering the bones more fragile and consequently more susceptible to fracture. A long-running programme of work at Roslin on laying hen osteoporosis has established the causes of the problem and studied factors influencing its occurrence. Exercise resulting from housing birds in enriched cages or other alternative systems can delay the onset of osteoporosis but fracture rates still remain high because of the more damaging impacts birds can have with perches and other environmental components. Good nutrition has a small effect in lessening the severity of osteoporosis but cannot prevent it. Genetics has the largest influence on osteoporosis and a breeding programme at Roslin based on divergent selection using a bone index comprising key bone indicators has resulted after 9 generations in a line of hens with over 50% greater bone strength. This improvement is additive to nutritional and environmental effects so this genetic approach should decrease fracture incidences in all husbandry systems. The experimental selection has been based on retrospective selection of progeny after post mortem analysis of dams at end of lay. It is time-consuming and not appropriate for large-scale commercial selection. Dead chickens can not reproduce! A system based on marker assisted selection (MAS) would be much more efficient. Studies on an F2 backcross between the divergently selected lines have identified a strong quantitative trait locus (QTL) for the bone index on chromosome 1. A related gene expression comparison identified genes associated with bone and cartilage development within the region of the QTL. The new project will identify functional single nucleotide polymorphisms (SNPs) within the region of the QTL, which can be used to select for improved bone quality in commercial birds.. The ultimate output of the project will be markers that can be used in MAS strategies for breeding laying hens and other types of poultry that have improved resistance to skeletal damage. Furthermore this will demonstrate that the approach can deliver a useable marker which can be extended for other QTL regions. The study will also identify candidate genes or regions controlling the genes and take the first steps to understanding how these genes influence variation in bone strength.