ANIHWA call 2: Better bone quality in laying hens

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.

The principle barrier to genetic progress in improving bone quality in laying hens is the lack of reliable selection methods. The methods which have been successful experimentally rely on killing birds to make the phenotypic measurements and retrospective selection.
The project has 3 components aimed at delivering markers to use prospectively rather than retrospectively in selection. The project combines the discovery of markers with their validation to ensure confidence in their use.
1) Molecular genetic approaches to define chromosomal loci controlling bone quality and the validation of markers derived from the studies to predict bone quality. To validate genetic markers in other genetic lines we will collect an extensive phenotype database from genetically distinct lines. We will use GWAS data already collected for association with bone strength and identify new markers.
2) The validation of a metabolic marker for its association with bone quality and its potential as a marker for selection. Our genetic and genomic approaches have identified the potential role of a metabolite in predicting bone strength possibly due to an effect on collagen crosslinking. Measurements will be made to establish the measurement of the metabolite and its predictive ability for bone quality.
3) A phenotypic approach to appraise bone quality phenotype in living hens that can be used as a direct assessment of bone quality. The ability of axial transmission of ultrasound in the surface of cortical bone to correlate with incidence of bone breakage will be studied. A fully replicated trial using nutritional treatments known to produce poorer bone quality will be established and the correlation of SOS with measurements of bone quality will be made. In the populations from 1 axial speed of sound sonography (SOS) of tibia and keel in young and end of lay hens will be made to estimate genetic parameters.

Eggs are an ideal source of nutrients in particular protein and have wide cultural acceptance. They are produced extremely efficiently however there are costs in terms of skeletal health which can represent a welfare issue. As the pressure grows for sustainable intensification the ability of hens to lay for longer is growing. To improve welfare and try and accommodate the conflicting demands it is necessary to find ways to improve by selection the bones of laying hens.
The principle benefit from this research will be methods to select hens to improve bone quality and to gain a greater understanding of the factors which underlie poor bone quality. This will translate in to benefit to the birds themselves and help to address the conflicting demands that agricultural production faces. This should address some of the welfare concerns that have been expressed over the egg production industry .
We have a long history of communication of our work to industry and scientists through scientific conferences including those of the WPSA which typically comprise 50% industry: 50% academia. We will present the work to these and more discipline specific conferences during the project and publish the results in both discipline led and wider industry publications during the project. To ensure wider dissemination appropriate industry days and agricultural events will be used along with a specific meeting organised to target the full range of organisations with an interest in this topic.
There are considerable opportunities to establish transfer of skills in the project. At The Roslin Institute we have a wealth of practical experience in assessing bone quality in chickens. Bob Fleming and Heather McCormack have in the region of 50 years of experience collectively. We already have plans for exchange of personnel between Granada and the Roslin Institute to learn histological and morphological techniques and this will strengthen this link. Similarly opportunities exist with SLU and indeed with Lohmann Tierzucht to transfer expertise. This transfer of knowledge will be critical for the future of research and practical progress on bone quality in laying hens in Europe. SRUC and the Roslin Institute are likely to have a greater alignment in coming years and the area of bone biology is an area where we are likely to be able to bring synergy to the topic. This project will increase the chances that this occurs