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Effects of Early Weaning on Postpartum Reproduction of Cows¹

U. S. Department of Agriculture, Clay Center, Nebraska 68933

Abstract

Three-Hundred-Eight Hereford, Angus, Charolais-cross (Charolais·Hereford and Charolais·Angus), Red Poll and Brown Swiss cows ranging in age from 2 to 11 years were used to investigate the effects of weaning 1 week before the beginning of the breeding period on postpartum reproduction. The calving period was 67 days and breeding began 27 days after the end of the calving period and extended for 42 days in November and December. Hereford, Angus and Charolais-cross cows were inseminated artificially approximately 12 hr. after the observation of standing estrus.

Weaning increased overall conception in the 42-day breeding period by 25.9% in 2-year-old cows, 15.6% in 3-year-olds and 7.9% in cows 4 years old and older (mature cows). There were 13.8% more 2-year-old cows and 15.6% more mature cows pregnant at the end of the first 21 days of breeding in the weaned than in the nonweaned groups, but these differences were not statistically significant.

Weaning increased the percentage of cows exhibiting estrus from calving to the end of the breeding period by 29% in 2-year-olds, 26.7% in 3-year-olds and 16.3% in mature cows. Weaning also increased the percentage of cows exhibiting estrus during the first 21 days of breeding by 39.2% in 2-year-olds and 23.5% in 3-year-olds, but it had no influence on the occurrence of estrus in mature cows. Weaning had no effect on inseminations per conception in the 2- and 3-year-olds, but the mature cows in the weaned group required 0.28 more inseminations per conception than those in the nonweaned group.

Among the cows bred, the intervals from calving to first estrus, calving to first breeding and calving to conception were not decreased by weaning. These intervals were affected by breed of cow and by calving date.

The increased percentage of the cows from the weaned group that conceived during the 42-day breeding period was the result of the effects of weaning on the occurrence of estrus, rather than on conception rate among those inseminated.

¹ The cooperation of the Nebraska Agricultural Experiment Station, University of Nebraska, Lincoln, is acknowledged.

² U.S. Meat Animal Research Center, A.R.S., U.S.D.A.

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