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

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Abstract
The 1st-lactation milk records of 20,850 artificially sired Holstein cows and their dams 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 herd-mate 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 2, 3, 4, or 5 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).