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Abstract
Studies were conducted in Georgia, Illinois and Maryland, representing three geographical regions of the United States, to determine the dose range of the orally active progestin, allyl trenbolone (RU-2267), for effective synchronization of estrus in swine. Animals that had displayed estrus at least once were group-fed for 18 days 5, 10, 20 or 40 mg of RU-2267 incorporated into a daily diet of 1.8 or 2.3 kg of feed. The numbers of gilts given each respective dose were eight, eight, eight and seven in Georgia, and six, five, six and six in Illinois. Five pigs received each dose in Maryland. Five primiparous sows were also treated with each dose in Maryland. Estrus was checked daily with a boar, and ovaries were examined by laparotomy 4 to 10 days after the estrous period following treatment or 15 to 24 days after the end of treatment in those animals that failed to display estrus. In Maryland, the interval from end of treatment to estrus (interval to estrus) differed (P<.05) between gilts (5.4 ± .3) and sows (6.0 ± .2) fed the 20-mg dose; but no other age differences were detected, and, as a result, data for gilts and sows were combined. The percentage of animals displaying a post-treatment estrus (estrous response) and the average number of corpora lutea (CL) formed at the post-treatment estrus (ovulation rate) were similar at the three locations; however, interval to estrus was shorter (P<.05) and the percentage of animals with follicular and(or) luteal cysts (percentage cystic) was lower (P<.05) in Illinois than in Georgia or Maryland. Estrous response, interval to estrus, percentage cystic and ovulation rate at the four doses of RU-2267 were, respectively: 5 mg—67%, 4.6 ± .2 days, 58% and 13.4 ± 1.3; 10 mg—82%, 4.3 ± .2, 22% and 16.4 ± .9; 20 mg—100%, 5.6 ± .2 days, 0% and 15.0 ± .8; 40 mg—100%, 6.1 ± .2 days, 0% and 14.7 ± .8. These results show that the most effective doses of RU-2267 for synchronizing estrus and ovulation without inducing development of follicular and(or) luteal cysts were 20 and 40 mg and that the minimum effective dose of RU-2267 for synchronizing estrus was between 10 and 20 milligrams.
1 Anim. Physiol. Res. Unit, USDA, SEA, AR, Richard B. Russell Agricultural Research Center. Athens, GA 30613.
2 Dept. of Anim. Sci., Univ. of Illinois, Urbana 61801.
3 USDA, SEA, AR, Beltsville Agricultural Research Center, Beltsville, MD 20705.
4 Dept. of Anim. and Dairy Sci., Univ. of Georgia, Athens 30602.
5 Reproductive Consulting Service, McHenry, IL 60050.
6 The authors wish to thank Dr. Larry Benyshek, Dept. of Anim. and Dairy Sci., Univ. of Georgia, for assistance in performing the statistical analysis. Progestin and financial support were provided by Roussel UCLAF, Paris, France.
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