Lactation Records Adjusted for Days Open in Sire Evaluation

Abstract

Holstein sires were evaluated by the Northeast Artificial Insemination Sire Comparison method from 227,232 mature equivalent 305-day first lactation milk records. Records were adjusted for period open, and sires were reevaluated by the same procedure. Evaluations changed even for sires having more than 2,000 daughters. The average change in evaluations was nearly zero, and the correlation of deviations between the two comparisons with the original evaluation was zero. Thus, changes in evaluation were independent of a sire's genetic value. A separate study indicated that Holstein adjustment factors can serve for all breeds on a practical basis. Heritabilities of days open were essentially zero for each breed.