Variation of Milk Records Within Paternal-Sib Groups

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 un-equM within group variances on the paternal sib estimate of heritability.The statistical model used to describe the data wasy~j = /x + s~ + e¢~ with o-~¢~ = o-~ +Estimates of the within sire-group O-ei.variances, cr~, were heterogeneous (P < .05)for each year of freshening, 1951-64.Average heritability estimates were .24,for 2