Effect of equine pituitary treatment on ovarian response and reproductive efficiency of old mares in a embryo transfer program

Abstract

The present study aimed to evaluate the effect of the use of low doses of equine pituitary extract (EPE) on follicular growth, ovulation rate and embryo recovery rates in old mares. Embryo donors (n=20) of Quarter Horse breed from a commercial embryo center aging 15 to 20 years old , were used during 3 consecutive cycles. The first and third cycles were used as control being the EPE treatment performed on the second cycle. During the 3 estrus mares were inseminated with cooled or fresh semen from the same stallion.The embryo flushing’s were performed on day 8 post-ovulation and were always followed by administration of PG. On the treated cycle, EPE injections (7mg twice daily i.m.) were started on day 8 after ovulation until a pre-ovulatory follicle was observed. The percentage of mares with more than one ovulation was compared by means using Fischer’s test and the mean number of ovulations and embryos, as well as follicular diameters, between cycles were compared using Student’s t test. The percentage of mares with more than one ovulation and number of ovulations were higher (p<0.05) in the EPE-treated cycle (65% of mares and 1.8 ovulations) than in the control cycle before (5% and 1.0) and after treatment (5% and 1.0). Also the mean number of embryos recovered per cycle were higher (p<0.05) on EPE treated cycle (1.0/cycle) than in no treated cycles (0.42/cycle). However the embryo rate per ovulation was similar (p>0.05) between no treated cycles (0.4 embryo/ovulation) and treated cycle (0.6 embryo/ovulation). The treatment with EPE allowed the recovery of embryos in stage of development more compatible with the embryonic age. The pregnancy rates of the transferred embryos was also similar between embryos recovered or treated (14/20-70%) and non treated cycles (9/17 -55%). Based on the results of the present experiment we can concluded that EPE treatment was able to increase the reproductive efficiency of old embryo donor mares, providing the recovery of at least one embryo on average per cycle.