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Observations on Fertility following Inseminations at Three Stages of the same Estrus¹

Wisconsin Agricultural Experiment Station, Madison

Abstract

Cows were checked for beginning of estrus three times daily at 8-hour intervals and for termination of estrus at 4-hour intervals. Time of ovulation was determined by rectal palpations at 4-hour intervals. The mean duration of estrus was 17.1 hours and the mean period from end of estrus to ovulation was 11.1 hours. The cows were artificially inseminated at the check when first observed in heat and again 12 and 24 hours later. Each of the inseminations was made with semen from a bull of a different breed. The order in which the semen from the different breeds was used was rotated. Paternity of the calves was determined by blood typing. Calves resulted from inseminations 34 hours before to 14 hours after ovulation. The mean interval from a fertile insemination to ovulation was 24.7 hours for the first, 11.0 hours for the second, and 6.6 hours for the third. Twenty-one cows calved from the first, 16 from the second, and 13 from the third insemination. Angus bulls sired 19, Guernseys 16, and Holsteins 15 of the 50 calves. The distribution of calves by inseminations and breeds was random. There was no indication that time of insemination had any effect on sex ratio. Three inseminations during the same estrus did not result in an exceptionally high conception rate.

Within the time limits of this study and the procedure employed, the time of insemination with respect to time of ovulation was not important to conception.

¹ Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. Supported in part by a grant from the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation.

² The authors are grateful to P. H. Phillips of the Dept. of Biochemistry for the use of the cattle for this study, to Wilmer G. Miller of the Dept. of Genetics for aid in performing the blood typing and analysis of results, and to Wisconsin Scientific Breeding Institute and Southern Wisconsin Breeders Cooperative for providing semen for Trials I and II and Trial III, respectively.