Response within Herd to Sire Selection

Effective sire selection should result in predictable differences among progeny groups within herds.National data from cows with lactations in 1979 gave withinherd regressions for Holstein yield on Predicted Difference of sire of 1.00 for milk and 1.01 for fat.First-lactation data gave regressions of 1.20 for milk and 1.13 for fat.Holstein herds were stratified into 10 classes by average milk yield of herd.Within-herd regressions of first-lactation yield on Predicted Difference of sire ranged from .71 for the lowest yield class to 1.49 for the highest yield class.Yield response to Predicted Differences of sires was related positively to herd yield, which suggests that sire selection for increased yield gives a greater return for herds with high yield than for herds with low yield.These results were supported by data from other breeds.Phenotypic variation within herds increased with herd yield, but coefficient of variation decreased.Heritabilities for yield from paternal half-sisters increased markedly across six classes of increasing herd yield for Holsteins.