Date of this Version
First lactation milk records of AI Holstein cows in the northeastern United States were analyzed for among and within-sire variation separately by year of freshening, class of herd production, and registry status of registered or nonregistered with a model that included effects of herd-seasons, sires of sampling daughters, and sires of daughters of proven sires. Heritability from the paternal half-sib correlation among records of daughters of sampling sires was similar for registered and nonregistered cows. Differences in heritability in different years and class of herd production were similar to those found in previous analyses that ignored registry status. Residual variances were similar for records of registered and nonregistered cows. Differences in variances by year and class of herd production also were similar to those found in previous analyses. Residual variances of milk records increased with time and class of herd production and in the same year were distinctly larger in herds with higher production than in herds with lower production. Residual variances of logarithms of milk records changed little with time but in the same year were distinctly smaller in herds with higher production than in herds with lower production. Residual variances of square roots of milk records increased somewhat with time but in the same year were similar in different classes of herd production.