ANIHWA call 2: Better bone quality in laying hens

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Laying hens can produce eggs economically for over a year; a highly digestible protein that has done much to improve world nutrition. However the long period of egg production can come with correlated problems of bone pathology. During egg laying oestrogen induces the formation of medullary bone, a form of calcium storage, in the cavities of the long bones. This bone is highly labile and turns over rapidly during shell formation. The bone forming osteoblasts are almost exclusively active during the formation of medullary bone during lay; however the osteoclasts, which reabsorb the medullary bone for calcium transport to the shell gland, act also on the structural cortical bone. This results in weaker bones (osteoporosis) and susceptibility to bone fracture. Non-cage systems exacerbate the problem with increases in bone fracture and keel bone deformities (>50%). With the demand for economical food unlikely to reduce, solutions to improve bone health are required.We have shown that there is the genetic potential within commercial pure lines to both lay a high number of eggs and have good bone quality. However the method of assessment of bone quality relies on killing the birds, which precludes subsequent breeding. To counter this, we have developed a number of approaches to discover genetic markers and we have identified a metabolic marker which explains variance in bone quality. Our aim will be to validate these markers and develop a novel phenotypic measurement for bone quality which does not require killing the hen.The project will build on studies recently completed or under way to detect genetic markers which predict bone quality which have been confined to one line of hens. The study will use quasi static strength measurement, density measurement as well as analytical techniques (infrared spectrometry, 2D X-ray diffraction) to study the chemistry and structure of bone to give a comprehensive insight in to factors defining bone phenotype. These populations, which will be from two types of hen, will be used to validate the markers for use in selection. The populations will also be used to validate the new phenotypic tool (quantitative axial ultrasound) and for the measurement of the blood metabolite which we have shown to be correlated to bone density. By using an array of approaches we expect to deliver practical solutions to breeders that will allow the genetic potential of laying hens with better bone to be realised.