J. Anim Sci.
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J. Anim Sci. 1980. 50:490-495.
© 1980 American Society of Animal Science
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Induction of Abortion in Mares with Equimate: Effect on Secretion of Progesterone, PMSG and Reproductive Performance1

E. L. Squires, R. B. Hillman2, B. W. Pickett and T. M. Nett

Colorado State University, Fort Collins 80523

Abstract

Thirty-two light-horse mares were confirmed to be pregnant and assigned to one of four treatments: (1) injected with 250 µg of Equimate on day 70 and again on day 77 if abortion had not occurred; (2) injected with 250 µg of Equimate on day 70 and every 24 hr until abortion occurred (maximum four injections); (3) injected with 250 µg of Equimate on day 70 and every 12 hr until abortion (maximum eight injections); and (4) injected with 250 µg of Equimate once only on day 35 of gestation. Mares were observed four times daily for incidence of abortion or side effects. Estrual behavior was monitored daily and follicular activity either daily or every third or fourth day until estrus and ovulation. Samples of jugular blood were obtained at 0600 hr day -1 and every 6 hr until the first day of estrus after abortion, or for 2 weeks after abortion if estrus had not occurred, or for 1 week after treatment for mares that had not aborted. A single injection of Equimate terminated pregnancy in all but one mare injected on day 35, but none of the mares given an injection on day 70 and 77 aborted. Multiple injections of Equimate beginning on day 70 of gestation terminated pregnancy in all mares. Fewer (P<.05) injections were required for abortion of mares injected daily. During the immediate week post-treatment, concentrations of progesterone decreased (P<.05) in all mares injected with Equimate, but overall concentrations were greater (P<.05) for mares injected once on day 70 than for those in the other three groups. Equimate did not affect secretion of PMSG in the day 70 group of mares. Estrus and ovulation after abortion were delayed (P<.05) for mares injected daily or twice daily beginning on day 70 compared to those injected once on day 35. Thus, rebreeding of these mares during the same breeding season in which they were aborted would be difficult.

Footnotes

1 Anim. Reprod. Lab. The authors wish to express to D. E. McGlothlin, G. E. Todter, C. P. Heesemann, V. M. LaBruzzo, J. G. Goodwin and Dr. R. K. Shideler for their assistance in collection of these data and to Diamond Laboratories, Des Moines, IA 50304 for supplying the MIP tests. Supported in part by ICI United States, Inc. Wilmington, DE 19897.

2 Present address: Dept. of Theriogenology, Cornell Univ., Ithaca, NY 14850.






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Copyright © 1980 by the American Society of Animal Science.