Estimation of genetic parameters for milk production in the first three lactations

Abstract

Variance and covariance components were estimated for milk-production traits in the first 3 lactations. The data set comprised 95 910 first, 74 088 second and 55 371 third lactation records of cows, sired by 603 black and white AI bulls in Lower Saxony (F.R.G.). Estimation was by two multiple trait restricted maximum likelihood procedures, differing by allowance of non-zero residual covariances (MT-O-REML and MT-REML). Further, correlations between traits within lactations were estimated using Henderson's method III (H-III). The results revealed a clearly antagonistic relationship between milk yield and percentages of fat and protein, with correlations in the range -0.40 to -0.50. In comparison with H-III estimates, genetic variances and especially covariances increased markedly when using REML and all available data. Error (co) variances were of the same magnitude for all methods used. Estimated genetic correlations between corresponding traits in Lactations 1 and 2 were greater than 0.90, while for Lactations 2 and 3 the correlation was unity. Results suggest that dairy performance in the first 3 lactations, at least in Lactation 2 and 3, genetically should be regarded as one trait.