Date of this Version
First lactation milk, fat, and protein yields for first lactations of 8044 Holstein cows in New York from 24 herds were used to estimate genetic and phenotypic covariances with an animal model by restricted maximum likelihood. Numerator relationships within herd, including those from sires, were utilized, although relationships across herds were ignored. Each analysis was terminated after 300 rounds of iteration. Average milk production (twice daily milking, 305-d lactation, mature equivalent) was 8630 kg. Estimates were obtained for each individual herd and groups of 3, 6, and 12 herds. Average estimates from separate analyses of the 24 herds were nearly identical to those from combined analysis. Heritability estimates from combined analysis were .36, .35, and .33 for milk, fat, and protein yield with standard errors of approximately .03. Genetic correlations were .72 for milk and fat, .88 for milk and protein, and .77 for fat and protein. Phenotypic correlations were .81, .91, and .82. Heritability estimates for individual herds were quite variable with standard errors of about .15. The largest environmental standard deviation for a herd was about twice the smallest. Estimates from only one analysis failed to converge-a group of three herds. All single herd analyses reached convergence as did the other 7 trios of herds and all sets of 6 and 12 herds.