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Regression of Records on Herd-Mate Averages

Department of Animal Husbandry, Cornell University, Ithaca, New York

ABSTRACT

Curvilinearity of regression and heterogeneity of linear regressions among sire groups of daughter records on herd-mate averages were studied for 44,975 first-lactation milk and fat records of New York Holstein cows sired by artificial insemination. Linear regressions were statistically heterogeneous. Similarly, curvilinear regression accounted for a statistically significant amount of variation above variation accounted for by linear regression. On a practical basis, however, neither group linear regressions nor curvilinear regression accounted for more than 1% additional variation over that accounted for by common linear regression. These results indicate that except for extreme cases where the average of the herd-mates is far above or far below breed average, the common linear regression of 0.88 is suitable for adjusting daughter averages for herd-mate level.