Fertilization and Embryonic Mortality Rates of Bulls with Histories of Either Low or High Fertility in Artificial Breeding

Abstract

On the basis of 3-day post-estrus slaughter data, fertilization rate was 76.9% for 26 heifers bred to bulls with histories of "low" fertility in artificial breeding and 96.6% for 29 heifers bred to bulls with histories of "high" fertility in artificial breeding. Percentage of normal embryos from the same number of heifers bred to low fertility bulls and slaughtered 33 days post-estrus was 57.7 and percentage of normal embryos from the same number of heifers bred to high fertility bulls and slaughtered 33 days post-estrus was 86.1. Percentage of heifers not pregnant, presumably because of embryonic mortality, was 19.6 for low fertility bulls and 10.5 for high fertility bulls. The difference of 9.1 percentage units between the 2 groups of bulls is not statistically significant. It would appear from the data that with high fertility bulls instances of repeat breedings are nearly always embryonic mortalities, whereas with bulls of low fertility both nonfertilization and early embryonic mortality occur.