Specific Combining Abilities Among Dairy Sires

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Abstract
All available 305-2x-M.E. lactation records in the New York Dairy Records Processing Laboratory from purebred Holstein cows having both their sire and maternal grandsire represented in a group of 200 A.L sires, were investigated for the importance of specific combining abilities among sires. The magnitude of the sire X maternal grandsire interaction component of variance was used to evaluate the importance of specific combining abilities. These data consisted of 39,160 lactation records from 17,361 cows. The interaction component of variance estimate for the milk deviations from herd-mates was 2.5% and .5% of the total variation for the first lactation and mean yield, respectively. Restricting the sire X maternal grandsire subclasses to 10 or more cows, the interaction component of variance estimate for the first-lactation deviations decreased to 1.4% of the total variation; the corresponding estimate for the mean yield deviations was essentially unchanged. Specific combining abilities among sires do not appear to rate important consideration in a general breeding program. Estimates of the additive, additive X additive, and dominance genetic components of variance were computed from the estimated sire, maternal grandsire, and sire X maternal grandsire components of variance.