eCG Concentration and Subsequent Reproductive Activity in Mares After Abortion at Day 70

The aim of the present experiment was to study the relationship between equine chorionic gonadotropin (eCG) concentration at and after abortion at day 70 and the subsequent reproductive activity. Twenty-two pregnant mixed breed, Criollo type mares with the same gestational ages (70-77 days), were induced to abort by digital puncture of fetal membranes. Immediately before induction, and for the next 10 weeks, eCG concentration and reproductive activity were monitored. Preabortion eCG was extremely variable, with a mean of 31.7 ± 28.1 IU/mL (range, 0.81-86.63 IU/mL). eCG decreased after abortion, and all mares reached 0 IU/mL within the next 70 days. Half of the mares ovulated again after a mean of 34.4 ± 9.8 days after abortion (range, 11-60 days); 90.9% of the mares that ovulated reconceived during the experiment. We observed threshold eCG concentrations below which mares are able to ovulate (2.9 IU/mL) and conceive (1.4 IU/mL). Preabortion eCG was significantly lower in mares that ovulated than in those that did not (P = .007) and lower in mares that reconceived than in mares that did not (P = .002). The interval from first to second conception was positively correlated with preabortion eCG concentration. Ovulatory and pregnancy rates were related to eCG concentration at abortion: mares having ≤35 IU/mL had significantly higher ovulatory (P = .024) and pregnancy rates (P = .002) than mares >35 IU/mL. No mares with >35 IU/mL at abortion became pregnant again. In conclusion, in mares aborted around day 70, eCG concentration can help to establish a functional prognosis for the same breeding season.