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A three point project has been undertaken to enhance the prediction of dairy cow lifespan, re-evaluate the economic weights of traits used in £PLI and to improve £PLI by the addition of health traits - somatic cell count and lameness.
Participants are Sustainable Livestock Systems, SAC, Edinburgh; ICAPB School of Biological Sciences, Edinburgh University, and Department of Agriculture and Food Economics, SAC, Aberdeen (Coffey, Stott and Brotherstone).
Genetic correlations between fore udder attachment, legs and feet composite, mammary composite, locomotion, production, somatic cell counts and lifespan have been built into the model.
Assuming an average cost of clinical mastitis of £81 in an affected lactation, the economic value of mastitis was put at £0.83 per % incidence. Similarly, assuming a treatment cost for lameness of £99 per lactation, the economic value of lameness was estimated at £0.99 per % incidence.
Traits chosen to best predict lifespan were fore udder attachment, legs and feet composite, mammary composite and somatic cell count. The accuracy of prediction was 53%.
A new £PLI was derived using both legs and feet and mammary composites to predict lifespan. It includes somatic cell count as a predictor of mastitis and locomotion as a predictor of lameness. In this index 78.7% of profit is from production and 21.3% from health and longevity.
Selection based on the new £PLI index in the UK is claimed to increase milk fat and protein content, prolong lifespan and reduce the increase in mastitis and lameness in dairy cows.
The findings were presented at the British Society of Animal Science Annual Conference, 5-7 April, York.