MULTIVARIATE-ANALYSIS OF TEST DAY MILK YIELDS OF BRITISH HOLSTEIN-FRIESIAN HEIFERS USING GIBBS SAMPLING

Estimates and posterior distributions of genetic and phenotypic varian ce matrices for test day milk records are obtained for 23 873 British Holstein-Friesian heifers, the progeny of 40 proven and 649 unproven s ires, using restricted maximum likelihood (REML) and Gibbs sampling me thods with two different prior specifications in a multivariate sire m odel. Results from the two methods are then compared. The REML estimat es and posterior expectations of heritability and individual test day records range from 0.28 to 0.42. Generally, heritabilities for test da y records are lowest at the start and highest in the second half of th e lactation. Estimates of genetic correlations between test day milk y ields range from 0.59 to 0.99, whilst those of phenotypic correlations are between 0.30 and 0.76, the correlations being highest for adjacen t tests. Bayesian inferences are more informative, but require much mo re computer time.