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The Effect of Time and Other Factors on the Non-Return to Service Estimate of Fertility Level in Artificial Insemination of Cattle

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

Evidence is presented indicating that in artificial insemination of cattle a significant proportion, varying up to 25 per cent, of the cows thought to be pregnant after one insemination, because they failed to show estrus during a time interval after insemination equivalent to two normal estrous cycles, actually returned for service at a later date. The difference between the percentage of cows that had not returned for reinsemination during 1 full month after the month of insemination (1-mo. non-returns) and those that did not return to service during the 4 subsequent months (5-mo. non-returns) was of the order of 12 to 15 percentage units. The magnitude of the difference varied with the age of the extended semen used for insemination and with experience in the artificial breeding program.