Aetiopathogenesis and genomic architecture of resistance to claw horn disruption lesions in dairy cattle

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The project will (i) determine and evaluate factors affecting the development of claw horn disruption lesions (CHDL) in dairy cattle; (ii) identify genomic markers (SNPs) and regions associated with animal resistance to CHDL development; (iii) identify and characterise causal genes and regulatory regions underlying pathways and networks associated with CHDL; (iv) develop and evaluate breeding tools and strategies for enhanced animal resistance to CHDL while at the same time improving other important dairy cattle traits. The study will involve 3,000 pedigree Holstein cows. Animals will be repeatedly examined by a qualified veterinarian for CHDL. In addition, mobility and foot conformation scores, digital cushion thickness, body condition score, claw temperature and backfat thickness will be recorded along with environmental temperature and animal activity and resting patterns. Blood levels of hormones, immuno-modulating cytokines, non-esterified fatty acids and beta-hydroxybutyric acid will also be measured. Statistical analysis of all these data, using mixed models, will reveal the impact of foot structure and anatomy, periparturient hormonal profile and inflammatory status, fat mobilisation and metabolic stress, and environmental and management conditions on CHDL. Interactions among factors will be also assessed. All animals will have genome-wide genotypes generated to identify SNPs and genomic regions associated with CHDL. Additive and dominance effects of significant SNPs and genomic heritabilities will be derived. Whole-genome sequencing and RNA-sequencing results on a subset of animals with extreme phenotypes and genotypes will be combined with pathways analyses and functional interpretation to reveal the underlying molecular mechanisms of CHDL development. All results will inform simulation studies to assess breeding strategies and tools (including a trait-specific SNP array) to enable breeding for resistance to CHDL development.

Compromised foot health leads to pain, reduced cow mobility and lameness, and constitutes a major welfare issue in dairy cattle. Painful lesions such as those disrupting the claw horn of the foot account for 90% of cases, represent the primary reason for veterinary interventions and lead to involuntary culling of affected animals, thereby posing serious threats to the sustainability and profitability of dairy farms. Many consider that lameness is currently the most significant welfare issue affecting dairy cattle in the UK because of the level of discomfort caused, the number of animals affected and the average duration of clinical episodes. Furthermore, studies have shown a significant adverse effect of lameness on milk yield both before and after a cow is diagnosed as lame that can last up to nine months. The total current cost to the UK dairy sector is estimated at £250 million or higher annually.

This project proposes a holistic approach to identify the key factors leading to the development of claw horn disruption lesions (CHDL). The project will develop a unique veterinary database and will combine complementary scientific expertise in order to develop a thorough understanding of the aetiopathogenesis of CHDL, while also developing practical knowledge and tools that can be used in genetic improvement programmes. Envisaged benefits from the outcomes are expected to apply at multiple levels:

1. Early identification of animals prone to development of CHDL will assist selection and replacement strategies, and minimise animal suffering.

2. Dairy farmers will directly benefit from reduced incidence of CHDL leading to decreased cost of involuntary culling. More animals will then be available for selection to improve productivity and other important traits. Fewer foot health problems will also signify enhanced animal welfare.

3. The dairy industry will benefit from advances and optimisation of genetic improvement programmes brought about by outcomes of the project. Currently, the economic benefits of genetic improvement in the UK exceed £100 million/year; about half of this is being realised by improvements in cow health and longevity. Project results will enhance animal health and welfare, and underpin the sustainability of the sector.

4. Improved health and welfare of the milking cows will enhance the public profile of dairy products and, eventually, the image of the sector and acceptability by consumers.