Meclofenamic acid extends donor-recipient asynchrony in equine embryo transfer

Abstract

Reasons for performing study: A level of synchrony between embryo and uterine environment is essential for the establishment of pregnancy when performing embryo transfer. The ability to extend the acceptable degree of asynchrony would allow more efficient use of recipient mares. Objectives: To establish if administration of the prostaglandin synthetase inhibitor, meclofenamic acid, to asynchronous recipient mares could widen the acceptable window of asynchrony for embryo transfer. Hypothesis: The prostaglandin synthetase inhibitory action of meclofenamic acid may act to suppress luteolysis and thereby allow for a greater degree of asynchrony between donor and recipient mares. Methods: A total of 72 Grade 1 horse embryos were transferred nonsurgically into the uteri of recipient mares that had ovulated 2 (n = 20), 3 (n = 20), 4 (n = 16) or 5 (n = 16) days before the donor. Half of the mares in each group were treated orally with 1 g meclofenamic acid, beginning on Day 9 after ovulation and continuing for 7 days after embryo transfer. Results: Comparison of recipient:donor asynchrony between treated and untreated mares was: +2 days, 9/10 pregnancies vs. 8/10 (P = 1.00); by +3 days, 8/10 vs. 2/10 (P = 0.025); by +4 days, 5/8 vs. 1/8 (P = 0.121); and by +5 days 3/8 vs. 0/8 (P = 0.20). In 10/11 meclofenamic acid-treated and 23/25 untreated recipient mares that failed to become pregnant, luteolysis occurred at the normal time (14-19 days) after ovulation. Conclusion: Treatment with meclofenamic acid supported the establishment of pregnancy in recipient mares that ovulated before the donors. However, meclofenamic acid appeared to provide this support in a manner other than by suppression of luteolysis. Potential relevance: Pregnancy rates can be increased in recipient mares that ovulate 3 days before the donor by administration of meclofenamic acid.