Date of this Version
Two samples of data from approximately 4000 Holstein cows were analyzed by REML with a multivariate (milk and fat yields) animal model for first lactations started in 1970 through 1977 and in 1978 through 1985 and also for first lactation records started in low, middle, and high production herds in 1978 through 1985 separately for California, New York, and Wisconsin herds. Heritability estimates for milk yield (similar for fat yield) ignoring category of herd production were .29 for 1978 and later and .34 for 1977 and earlier. Estimates for low, middle, and high production herds were .23, .29, and .36. Estimates of genetic correlation between milk and fat averaged .62 for 1978 and later and .73 for 1977 and earlier; for 1978 and later these estimates were greater for California than for New York and Wisconsin, .70 vs. .58 overall. Phenotypic and environmental variances associated with low production herds were less than for middle and high production herds, but differences between middle and high herds varied by state and sample. The pattern of estimates of genetic and environmental parameters suggests that differences between California, New York, and Wisconsin are not very important for genetic evaluation procedures. Production of herds does seem important.