Genetic Differences Among Holstein-Friesian Herd Improvement Registry Herds

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Abstract
Genetic differences among 442 Holstein- Friesian I:fIR herds that had been on test from March, 1952, to April, 1961, were examined. First lactations initiated at under 36 months of age for 37,890 individuals were studied by two approaches. In the first, differences between bull breeder herds were compared by the progeny test evalua- tion of sires produced in a specific herd but progeny tested in another herd. Among 19 breeder herds that sold a large number of sons to other herds, four times the variance of breeding values of those sons, attributable to the herd in which they were bred, represented 12.4 and 18.7% of the herd component for milk yield and per cent fat. The mean genetic merit of 282 sons originating from these breeder herds was 92 kg o£ milk above the 479 sons from nonbreeder herds and 143 kg above the 67 sires originating from outside the United States. The second approach involved a comparison of the herd component of variance from multiherd progenies of sires with the herd component from single-herd progenies. The fraction of the herd vari- ance for the population of 442 herds that was genetic was 9.3% for milk yield and 8.9% for fat per cent. The results indicate that the genetic differences among these Holstein HIR herds are small but real, contributing about 10% of the variance among herd averages for milk. While the herd average would be more useful to correct for environmental differences among herds, it also should receive some positive attention for estimating genetic differences between individuals in different herds.