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Effect of Genetic Trend on Sire Evaluation

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

ABSTRACT

The contemporary comparison evaluation of 235 Holstein sires used in artificial insemination having daughters whose first lactations began during the period 1951–1959 were compared with the same evaluations adjusted for trend in genetic merit of their naturally sired contemporaries. Correlations were computed between the adjusted and unadjusted comparisons for all sires, regardless of number of daughters, for the 38 sires having the largest number of daughters, and within contemporary time groups. All estimated correlations were near unity for both milk and fat yield. These estimates indicate that with the present relatively slow change in genetic merit the trend in genetic merit need not be considered in the evaluation of contemporary young sires. If comparisons are desired between sires used several years apart, then it may be necessary to adjust for genetic trend.