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Genotype and Environment in Sire Evaluation

Department of Animal Husbandry, Cornell University, Ithaca, New York

ABSTRACT

First (45,876) and second (39,261) lactation records of New York A.I. Holstein daughters were divided into four groups depending on the level of their adjusted herd-mate averages relative to the DHIA season average. The high level was greater than 1,000 lb of milk above the season average, whereas the low level was more than 1,000 lb of milk below season average.

Components of variance for sires and within sires were then estimated for each level from deviations of daughter records from their adjusted herd-mate averages. Genetic correlations between the genotypes in different environments were estimated. Application of the formula for relative genetic progress indicates that it may be advantageous to evaluate sires from daughter performance in all except the low-level herds. Excluding about a quarter of the herds would, however, decrease the number of young sires which could be tested. Considering both of these factors it seems preferable not to exclude any herds unless contract herds were being used to test young sires. Since the genetic correlations are high (near unity), the evaluation of the sires would be nearly the same in all herd levels.

Results indicate that although there is little, if any, genotype-environmental interaction in the usual sense (ranking of sires in different environments), there is another form of genotype-environmental interaction: genetic variability is evidently different from one environmental level to another—the higher the level, the more genetic variability. The fraction of the total variability which is genetic is also lower in the lower levels of environment than in the higher levels.