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Ovarian Functions, Intervals between Estrus, and Conception Rates in Dairy Cattle¹

Department of Animal Husbandry, Cornell University, Ithaca, New York

ABSTRACT

A considerable number of research reports giving the intervals between estrus are available. These also list the percentage of females that do not show estrus at the expected time, but the ovarian condition or the causes of these irregularities either were unknown or were not described.

This experiment was conducted to determine ovarian conditions or functions and their influence on regularity of estrus and conception rates in dairy cattle. Obviously, such knowledge would provide more complete information about reproduction in dairy cattle, especially on the advisability of recommending service to cows during irregular estrus as determined by the chances for conception.

Chapman and Casida (6) reported that 40% of 690 clinically normal cows showed estrous cycles less than or greater than 17 to 24 days. Asdell et al. (2) found that 16% of 167 estrous cycles did not fall within the period of 18 to 24 days. Ellenberger and Lohmann (7) reported that 30% of 274 estrous cycles observed in cows occurred at intervals less than or greater than 17 to 25 days.

¹ Supported in part by state funds and in part by funds from the regional project N. E.-l, entitled Causes and Prevention of Reproductive Failures in Dairy Cattle, a cooperative study by agricultural experiment stations in the northeastern region and the Dairy Research Branch, USDA.