Date of this Version
Records of the first three lactations of cows were obtained from the file of the Dairy Herd Testing Association in Hokkaido. The data were divided into 10 files containing approximately 24,000 cows each. The derivative-free REML method was used to estimate variances with a repeatability model. The model contained herd-year, calving month, and the linear and quadratic effects of age at calving as fixed effects; additive genetic, permanent environmental, and temporary environmental effects were the random effects. Estimates from the 10 data files were pooled into a simple arithmetic mean. Empirical standard errors were. calculated from the samples. Average estimates of heritability were the same for milk and fat yields (h2= .30). Heritabilities for protein (h2= .26) and SNF yields (h2= .27) are slightly lower than those for milk and fat yields. Estimates of repeatabilities, .52 to 254, are considerably different from those now used for genetic evaluations in Japan.