Evaluation of three equine FSH superovulation protocols in mares

Superovulation could potentially increase embryo recovery for immediate transfer or cryopreservation. The objectives were to evaluate the effect of pretreatment with progesterone and estradiol (P + E) on follicular response to eFSH and compare doses of eFSH and ovulatory agents on follicular development and ovulation in mares. In Experiment 1, 40 mares were assigned to one of four treatment groups. Group 1 consisted of untreated controls. Group 2 mares were administered eFSH without pretreatment with P + E. Group 3 mares were administered P + E for 10 days starting in mid-diestrus followed by eFSH therapy. Group 4 mares were administered P + E for 10 days followed by eFSH therapy. All treated mares were administered 12.5 mg eFSH twice daily and prostaglandins were given on the second day of eFSH therapy. Mares were bred with fresh semen the day of hCG administration and with cooled semen the following day. The numbers of preovulatory follicles and ovulations were lower for mares treated with P + E prior to eFSH treatment. Pretreatment with P + E in estrus also resulted in a lower embryo recovery rate per ovulation compared to the other two eFSH treatment groups. In Experiment 2, two doses of eFSH (12.5 and 6.25 mg) and two ovulation-inducing agents (hCG and deslorelin) were evaluated. The number of preovulatory follicles was greater for mares given 12.5 mg of eFSH compared to mares given 6.25 mg. Number of ovulations was greatest for mares given 12.5 mg of eFSH twice daily followed by administration of hCG. Embryo recovery per flush was similar among treatment groups, but the percent of embryos per ovulation was higher for mares given the low dose of eFSH. In summary, there was no advantage to giving P + E prior to eFSH treatment. In addition, even though the lower dose of eFSH resulted in fewer ovulations, embryo recovery per flush and embryo recovery per ovulation were similar or better for those given the lower dose of eFSH.