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

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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. Copyright © . .