Effects of Sire and Interaction of Sire with Ration on Efficiency of Feed Utilization by Holsteins

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Abstract
First lactations of 289 daughters of 17 Holstein sires were used to assess the effects of sire and interactions of sire with ration or feed intake, milk yield and efficiency of feed utilization. In each of 2 trials, 1/2 of the daughters of a sire were fed a high forage ration and the other 1/2 were fed a standard (Trial I) or a high grain ration (Trial II). By methods of least squares sire effects were significant in both trials for yield and efficiency, but only in 1 trial for feed intake. Differences in milk yields appeared to account for differences among sires in efficiency. Interactions of sire with ration were significant only for fat yield, fat-corrected-milk yield and efficiency of feed utilization in Trial I. When the records of the daughters of 1 bull from New Zealand were removed from Trial I data, there were no significant interactions of sire with ration in either trial. Regressions of daughter deviations on sire predicted difference were positive on all rations for milk yield, feed intake and efficiency traits but tended to be greater under the more liberal feeding regime in each trial. Daughters of sires with high predicted differences used less of their nutrient intake for increase of body tissue and more for milk yield. Heritability of efficiency of feed utilization was .47, and efficiency had a high genetic correlation with feed intake and milk yield (.71-.95). Selection for high milk yield appears to be a practical means of securing genetic improvement in efficiency of feed utilization.