Heterogeneity of Daughter Variances of Sires for Milk Yield

Abstract

Milk yields for 1st 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 yr-mo. 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 yr 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-.29) with large SE (.11-.14). Individual genes or linkage groups may have relatively large effects on milk production.