Abstract
DHIA data representing 24,853 daughter-dam comparisons for 263 Holstein A.I. sires were studied to determine the usefulness of information on a sire's mates (dams of daughters) in sire evaluation. Although there was a mean bias of 41lb of milk per sire, due to selection of mates, the relative ranking of the bulls was the same (rank correlation = +0.998) when daughters’ deviations alone were used as when both daughter and dam deviations were employed for ranking. If point estimates of a bull's breeding value are desired, failure to employ the mates’ deviations will, on the average, result in an overestimate of the sire's merit. Analyses of variance indicated that the bulls’ mates were equally as variable as the daughters of the bulls. A heritability estimate for milk yield of 0.24 was obtained by daughter-dam regression.
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