Induction of abortion in mares with equimate: effect on secretion of progesterone, PMSG and reproductive performance.

The research paper discusses a study conducted on thirty-two light-horse mares to ascertain the impact of Equimate, a drug used to induce abortion, as well as the drug’s effects on progesterone secretion, PMSG secretion, and overall reproductive performance. The results indicate that multiple administrations of Equimate could successfully terminate a pregnancy, with progesterone levels dropping following treatment. However, the findings also highlight the possibility of delay in estrus and ovulation following abortion, especially in mares administered the drug more frequently.

Experimental Design and Process

• The experiment involved thirty-two light-horse mares that were confirmed to be pregnant. They were randomly divided into four groups, each subjected to a different treatment protocol involving Equimate administration.
• The first group received 250 micrograms of Equimate on the 70th day of pregnancy, and again on the 77th day if abortion didn’t occur. The second group received the same dose every 24 hours starting from the 70th day until abortion occurred, with a maximum limit of four injections. The third group received the same dose every 12 hours from the 70th day until abortion occurred, capped to a maximum of eight injections. The last group received a one-time dose of 250 micrograms on the 35th day of gestation.
• All mares were monitored four times daily for signs of abortion or side effects. Additionally, their estrual behavior and follicular activity were tracked daily, or every third or fourth day until estrus and ovulation.
• Blood samples were drawn at 0600 hr day -1 and every six hours until the first day of estrus after abortion, or for two weeks after abortion if estrus did not occur. For mares who didn’t abort, samples were obtained one week after treatment.

Key Findings

• Except for one mare in group 4, a single dose of Equimate successfully terminated the pregnancy in all mares in this group. However, none of the mares in the first group (who received injections on the 70th and 77th day) aborted. Multiple Equimate injections starting from the 70th day led to successful abortion in all mares.
• Progesterone levels decreased in all mares post-Equimate treatment. However, overall progesterone concentrations were significantly higher in mares who received only one injection on the 70th day compared to the other groups.
• Equimate did not impact PMSG secretion in the group of mares that were injected on the 70th day.
• The occurrence of estrus and ovulation was delayed in mares injected daily or twice daily starting on the 70th day, compared to those injected once on the 35th day. The study concludes that this delay could complicate rebreeding of these mares in the same breeding season.