Effect of Rams on Progestin-Treated Ewes

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Abstract
Two experiments were conducted to study the effect of teasing with vasectomized rams at the first expected estrus following progestin treatment near the onset of the breeding season on ewe performance at the second expected estrus. In experiment I (175 ewes), vaginal sponges containing 20 mg flurogestone acetate were inserted on July 28 (day 1) and removed on day 13. On days 13 through 28, 88 ewes were pastured with five vasectomized rams. The remaining 87 ewes were pastured without teaser rams. On day 29, the ewes in each group were assigned at random to be inseminated artificially (AI) or mated naturally (NM) as they exhibited estrus on days 29 through 32. Teasing increased the number of ewes showing estrus to 94.3% compared to 50.5% for non-teased ewes (< 0.01). Teasing had no effect on conception or lambing rates of ewes mated. Type of mating had a significant effect on conception rate (79.5 and 51.0% for NM and AI, respectively). In experiment II, three treatment groups were: (1) control (69 ewes); (2) teased (65 ewes) and (3) teased, progestin-treated (63 ewes). Progestin treatment and teasing were on the same schedule as described for experiment I. Ewes were mated naturally and the breeding period was the same as in experiment I. The percent of ewes showing estrus during the 4-day period was greater (P < 0.01) in teased, progestin-treated ewes than in control or teased ewes. Conception rate at first service was lower (P < 0.05) in control ewes (39%) compared to teased (64%) and teased, progestin-treated ewes (79%). Conception rates for the latter two groups did not differ. Percentage of ewes lambing by February 18 was lower (P < 0.05) in teased ewes (75%) than in teased, progestin-treated ewes (92%) but did not differ in either of these groups from the value for control ewes (85%). Lambing rates at first service averaged 1.12 and did not differ due to treatment. Lambing rate overall was higher (P < 0.05) among control ewes (1.83) than among teased, progestin-treated ewes (1.55) but not higher than among teased ewes (1.72). Copyright © 1973. American Society of Animal Science. Copyright 1973 by American Society of Animal Science

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