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

Estimates of posterior distributions of genetic and phenotypic paramet ers and functions of them for individual test day milk yield are obtai ned for 28 873 British Holstein-Friesian heifers, the progeny of 40 pr oven and 649 unproven sires, using restricted maximum likelihood (REML ) and Gibbs sampling methods with a univariate sire model. Results fro m the two methods are then compared. It is found that the posterior ex pectations and REML estimates of the parameters are fairly similar. Th e marginal posterior expectation and REML estimate of heritability for lactation milk yield are 0.49 and 0.50, respectively. Heritability es timates for individual test day records range from 0.27 to 0.40, whils t the posterior expectations are between 0.28 and 0.42. Generally, her itabilities for test day records were lowest at the start and highest in the second half of the lactation. Gibbs sampling requires substanti ally more computing than REML estimation, but provides a more informat ive analysis.