Variation of Milk Records Within Paternal-Sib Groups

Abstract

Differences between daughter-dam and paternal sib estimates of heritability of first lactation milk yield have not been explained for New York data. Deviations of first lactation records from herdmate means of 155,070 artificially sired Holsteins were analyzed to examine the effect of unequal within group variances on the paternal sib estimate of heritability. The statistical model used to describe the data was yij = μ + si + eij with σ yi2=σs2+σ ei2. Estimates of the within sire-group variances, σ12ei, were heterogeneous (P