Reproductive characteristics of spontaneous single and double ovulating mares and superovulated mares.

For embryos collected from mares 7 days after ovulation, embryo recovery for single-ovulating mares was 53% compared to 106% for double-ovulating mares. Pregnancy rates 50 days after surgical transfer were 68 and 129%, respectively. Concentrations of LH were similar during the periovulatory period for cycles which included single or double ovulations. Horse pituitary extract given for 5.5 days resulted in greater than or equal to 2 ovulations (mean 3.8) in 26 of 28 mares and 2.0 embryos were recovered per donor compared to 0.65 for controls. Non-surgical pregnancy rates for embryos collected from superovulated mares 6 and 8 days after ovulation (18 of 46; 39%) were identical to those obtained for untreated controls (12 of 31; 39%). The overall pregnancy rate for superovulated donors, which provided 2-4 embryos, was 120%. Since the viability of multiple embryos collected from spontaneous and induced multiple-ovulating mares was equal to that of embryos from single-ovulating mares, collection and transfer of embryos from these mares will increase the efficiency of horse embryo transfer.