Some factors affecting the reproductive efficiency in beef cattle

The ovaries of a total of 346 cows in three University of Tennessee Agricultural Experiment Station herds were palpated within one week prior to the beginning of the breeding season, to determine if the females had resumed postpartum ovarian activity. The numbers and ages of animals within the three herds were: (1) Alcoa herd-78 head, 2- to 4-years, (2) Ames Plantation herd-106 head, 2- to 13-years, and (3) Tobacco Experiment Station herd-172 head, 1- to 7 years of age. Overall the ovaries of only 46 percent of the females contained a corpus Iuteum. In the Alcoa herd, presence of a sterile bull with the cows for 45 days prior to the beginning season did not influence the numbers of cows with corpora lutea. Estimated conception rates in the Tobacco Experiment Station herd, by 21 day periods of the breeding season, indicated that 38 percent of the females conceived during the first 21 day interval of the breeding season. However, 64 percent of the cows which became pregnant during this period had a corpus luteum at the beginning of the breeding season. Extrapolation of these results to all three herds suggests that had all cows been cycling at the beginning of the breeding season, about 67 percent more calves would have been born during the first three weeks of the calving season. This emphasizes the importance of the reproductive status of the cow at the beginning of the breeding season on her subsequent reproductive performance.