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The Bull as One Cause of Delayed Returns to Service in Artificial Breeding

Department of Dairy Science, University of Illinois, Urbana

R. W. Bratton and R. H. Foote

Department of Animal Husbandry, Cornell University, Ithaca, N. Y.

ABSTRACT

The results or statistical studies indicate that the semen of bulls is one of the major sources of origin of the significant differences observed from bull to bull in the incidence of embryonic mortality, as measured by the difference between 1- and 5-mo. non-returns to service in artificial breeding. The level of embryonic mortality was negatively and highly significantly correlated with the original fertility level of bulls as measured by 1-mo. non-returns, the correlation coefficients being in the neighborhood of - 0.6 to - 0.7. A significant effect of the season of the year on apparent embryonic mortality was indicated, the maximum effect being produced from inseminations in January, February and March, the minimum being in May and June.