THE GENETIC EVALUATION OF BEEF SIRES USED FOR CROSSING WITH DAIRY-COWS IN THE UK - 2 - GENETIC-PARAMETERS AND SIRE MERIT PREDICTIONS FOR CALVING SURVEY TRAITS

Genetic parameters were estimated for traits recorded in a calving sur vey for beef sires used in commercial dairy herds in England and Wales . The Jive traits included in the survey were calving difficulty score , calf mortality to 48 h after birth, gestation length, and subjective ly assessed calf size and conformation. The data file examined include d over 88 000 records, on 323 sires of eight beef sire breeds, namely Aberdeen Angus, Belgian Blue, Blonde d'Aquitaine, Charolais, Hereford, Limousin, Piedmontese and Simmental. Estimates of heritability and ge netic and phenotypic correlations were obtained for all traits by REML procedures using a sire model. The effects of cow age, calf sex, year and season of the calving and sire breed were included in the model, together with interactions. Heritability estimates were 0.09 (s.e. 0.0 1) for calving difficulty score, 0.32 (s.e. 0.03) for gestation length , 0.02 (s.e. 0.003) for mortality, 0.09 (s.e. 0.01) for calf size and 0.06 (s.e. 0.01) for calf conformation. Heritability estimates for the scored categorical and binomial (mortality) traits were also obtained using threshold model analysis. As expected, these estimates were hig her than the REML estimates; 0.16 (s.e. 0.01) for calving difficulty s core, 0.08 (s.e. 0.01) for mortality, 0.14 (s.e. 0.01) for calf size a nd 0.09 (s.e. 0.01)for calf conformation. Calving difficulty score was strongly correlated genetically with calf size (-0.84), mortality (0. 74) and calf conformation (-0.72), and moderately correlated with gest ation length (0.26). Calf size and conformation were very highly corre lated genetically (0.86), and both were also strongly correlated with mortality (-0.63 and -0.52 respectively). In all cases, the genetic co rrelations were stronger than the phenotypic correlations. Sire geneti c merit was predicted for all traits and the distribution of these pre dictions is described. Sire predictions of genetic merit for calving d ifficulty score on the underlying scale were backtransformed to predic t the expected incidence of serious difficulties in future calvings an d these predictions are illustrated for the major sire breeds.