165 OVARIAN RESPONSE AND EMBRYO RECOVERY RATES OF OLD MARES TREATED WITH A LOW DOSE OF EQUINE PITUITARY EXTRACT

Abstract

Mares older than 15 years have low embryo recovery rates, mostly because of disturbances in follicle or oocyte maturation and early embryonic development. A recent publication showed that circulating LH level is lower in older mares (Ginther et al. 2009 Theriogenology 5, 780-788). Equine pituitary extract (EPE) is rich in LH and consequently is able to increase circulating LH levels after injection into mares. The present study aimed to evaluate the effect of low doses of EPE on follicular growth, ovulation rate, and embryo recovery rates in older mares. Embryo donors (n = 20) were Quarter Horses from a commercial embryo center that ranged in age from 15 to 20 years. Donors were used during 3 consecutive cycles. The first and third cycles were used as control cycles, and the EPE treatment was performed on the second cycle. During estrus in each of the 3 cycles, mares were inseminated with cooled or fresh semen from the same stallion and received an injection of deslorelin (1 mg i.m.) upon detection of at least 1 follicle of 35 to 40 mm in diameter. Embryo flushes were performed on Day 8 post-ovulation and were followed by administration of prostaglandin. On the treated cycle, EPE injections (7 mg twice daily i.m.) were started on Day 8 after ovulation until a preovulatory follicle was observed. The percentage of mares with more than one ovulation was compared using Fisher’s test. The mean number of ovulations and embryos, as well as follicular diameter, was compared using Student’s t-test. The percentage of mares with more than one ovulation as well as the number of ovulations per cycle were higher (P < 0.05) in the EPE-treated cycle (65% of mares and 1.8 ovulations, respectively) than in the control cycles before (5% and 1.0) and after treatment (5% and 1.0). Also, the mean number of embryos recovered per cycle was higher (P < 0.05) in EPE-treated cycles (1.0) than in nontreated cycles (0.42). However, the embryo recovery rate per ovulation was similar (P > 0.05) between nontreated (0.4 embryo) and treated cycles (0.6 embryo). Pregnancy rates of the transferred embryos were also similar between embryos recovered on treated (14/20; 70%) and nontreated cycles (9/17; 55%). The daily growth of the dominant follicle was not altered by the EPE treatment. However, embryos recovered during treated cycles were more advanced in development than controls, with more embryos (P < 0.05) classified as morula or early blastocysts when recoverd during nontreated (58%) v. EPE-treated cycles (0%). Based on the results of the present experiment, we can conclude that EPE treatment was able to increase the reproductive efficiency of older embryo donor mares. The improvement in embryo recovery rates on EPE-treated cycles seemed to be more related to the increase in the number of ovulations per cycle than with an improvement in embryo viability.