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Heterogeneity of Daughter Variances of Sires for Milk Yield¹

Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061

ABSTRACT

Milk yields for first lactations of Holstein cows were used to determine the magnitude and possible causes of differences among sires in variability of daughters. Sires differed greatly in daughter variability. The model with largest multiple correlation for explaining these differences included linear, quadratic, and cubic effects of mean milk yield of daughters, mean and variance of contemporary yield, variance of relative producing abilities of mates, number of contemporary sires, and number of year-months in which daughters calved. Multiple squared correlation was .18.

Analysis of variance of sire by herd subclasses indicated approximately equal contributions of sires and herds to differences in variation of daughters. Repeatabilities of sires for variance of daughters across years were .29 and .32 with minimums of 25 and 50 daughters where daughters in different years were required to be in different herds.

Heritabilities of variance of daughters for sires by regression of son on sire were low to moderate (–.14 to .29) with large standard errors (.11 to .14). Individual genes or linkage groups may have relatively large effects on milk production.

¹ Published with the approval of the Director of the Agricultural Experiment Station.

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