Genetic correlations of somatic cell count and conformation traits with herd life in dairy breeds, with an application to national genetic evaluations for herd life in the United Kingdom

Genetic correlations (r ) between Lifespan (LS) and conformation traits in the Ayrshire breed were obtained from data on g 8087 heifers which calved between 1976 and August 1990. The r were estimated from a series of multivariate analyses g applying an animal model restricted maximum-likelihood procedure. The genetic relationship between LS and somatic cell counts (SCC) was studied in the Holstein Friesian (HF), Ayrshire (AYR) and Jersey (JER) breeds. Estimates of r between g LS and SCC were obtained from a bivariate analysis fitting a sire model. The four type traits with the largest r with LS g were foot angle (0.47), udder depth (0.46), fore udder attachment (0.28) and teat length (20.28). The estimates of rg between LS and SCC varied from 2 0.32 (HF) to 2 0.11 (JER); higher SCC resulted in lower herd life. Genetic evaluation for LS in the United Kingdom involves a bivariate analysis utilising direct lactation information and indirect information from conformation traits. The design matrices for the direct and indirect traits are different and either trait could be missing. A computing strategy implemented for the national evaluation of herd life that handles these problems is presented in addition to the results from the first official evaluation. Bull predicted transmitting abilities (PTAs) for LS ranged from 2 0.8 to 1.4 lactations; most bull PTAs were within the range of 60.5 lactations. The predicted difference in LS is about one lactation between daughters of extreme bulls when those with at least ten daughters were considered. A slight positive genetic trend was observed for LS in all breeds.  2000 Elsevier Science B.V. All rights reserved.