Hormonal changes associated with induced late abortions in the mare

Area of Science:

• Veterinary Medicine
• Reproductive Biology
• Endocrinology

Background:

• Pregnancy termination in mares can be achieved through hormonal interventions.
• Understanding the physiological responses to different abortifacient agents is crucial for reproductive management.

Purpose of the Study:

• To compare the efficacy and physiological effects of prostaglandin F-2 alpha (PGF-2 alpha) and a combination of oestradiol benzoate and oxytocin for inducing abortion in mares at approximately 150 days of gestation.

Main Methods:

• Two pregnant mares were treated with PGF-2 alpha twice daily until abortion.
• Two pregnant mares received a combined treatment of oestradiol benzoate and oxytocin.
• Hormonal concentrations (15-ketodihydro-PGF-2 alpha, progesterone, relaxin, oestrone sulphate, PMSG) were monitored before and after treatment and abortion.

Main Results:

• Both treatments induced abortion, with PGF-2 alpha treated mares aborting between 37-61 hours and oxytocin-treated mares between 13-27 hours.
• Oxytocin treatment resulted in stronger uterine contractions and disrupted fetal membranes, suggesting potential uterine damage, indicated by a large increase in 15-ketodihydro-PGF-2 alpha.
• PGF-2 alpha treatment led to an immediate return to basal 15-ketodihydro-PGF-2 alpha levels post-abortion.
• Oestrone sulphate levels decreased rapidly after oxytocin but showed an initial increase followed by a decrease after PGF-2 alpha.
• Progesterone and relaxin decreased in both groups, reflecting placental function decline.

Conclusions:

• Both PGF-2 alpha and oxytocin can induce abortion in mares, but oxytocin appears to be faster acting and associated with more intense uterine activity.
• Hormonal profiles differ between the two treatments, with oxytocin potentially causing more significant uterine trauma.