Heritability Estimates of Milk Production with Different Numbers of Records per Sire by Herd Subclass

The first-lactation milk records of 20,850 artificially sired Holstein cows and their darns were analyzed by a sire-by-herd, variance components model to determine if unequal numbers of records in the filled subclasses had any effect on the paternal half-sib correlation or the daughter-dam regression. The variance components were estimated with the number per subclass held constant at 1, 2, 3, 4, or 5. The records were also analyzed as deviations from herdmate averages. The analysis of deviations with one observation per subclass gave the highest heritability estimate from daughter-dam regression, .40, and the lowest from paternal half-sib correlation, .23. Analyses of deviations with two, three, four, or five observations per subclass gave approximately the same estimates of heritability from both daughter-dam regression (.31, .32, .29, and .23) and paternal half-sib correlation (.32, .31, .27, and .36)