The effect on conception rate of mixing semen from first and second ejaculates

Abstract

Abstract Inseminations were made with semen from first and second ejaculates used separately and mixed on a within-sire basis. The average conception rate (CR = percent 49-day non-return rate) for inseminations from first ejaculates did not differ significantly from the CR for second ejaculates (69.7 v. 68.8). The CR for the mixed samples was similar to the average CR predicted from the known CR's for the constituent ejaculates (69.7 v. 69.4). The mixing of semen resulted in a significant reduction in the residual variation for CR from that observed with CR's for first or second ejaculates. This reduction in variation was primarily the consequence of averaging CR differences between individual ejaculates by mixing before final processing. Consequently, experiments in which semen extenders are to be compared should be based on a split-ejaculate technique. The results with the mixed samples contrasted with those that may have been expected in the light of previous reports based on heterospermic inseminations. The CR's for the mixed samples did not tend towards the CR of either component ejaculate.