Genetic and Maternal Influence on the First Three Lactations of Holstein Cows

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Abstract
Milk records of up to the 1st 3 lactations of artificially sired Holstein daughters and their dams were used to estimate heritability from both daughter-dam regression and paternal half-sib correlation. The within-herd estimates from records expressed as deviations from herd-mate averages were .37, .30, and .24 from daughter dam regression for the 1st 3 lactations; and the corresponding estimates from half-sib correlation were .24, .21, and .23. These results suggest a large maternal effect in the 1st lactation, a small amount in the second, and little in the 3rd lactation. Analysis of the records not as deviations gave the same pattern for the daughter-dam regressions, but confounding of sires with year-seasons apparently biased the half-sib correlations upward. The consequence of considering unequal heritability for different lactations if the apparent difference is due to maternal effects is illustrated for selection for 1st lactation breeding value from up to 3 records on the cow herself and on her dam.