A derivative-free restricted maximum likelihood algorithm to fit an animal model was used to estimate variances and covariances for milk, fat and protein yields among yields of the first three lactations, using 110,779 records of 54,634 Holstein cows from California Heritability estimates for milk, fat and protein yields were, respectively, .34, .35 and .40 for first, .31, .33 and .39 for second and .27, .31 and .37 for third lactation. Estimates of genetic correlations among lactation yields, in general, were greater than .80. The phenotypic correlations varied from .52 to .66 and were similar for the three yield traits.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 17. Genetics and breeding of dairy and beef cattle, swine and horses, , 34–37, 1994
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