The effects of equine follicle stimulating hormone (eFSH) on mare fertility

A series of experiments were designed to study the effects of a purified equine pituitary extract product containing a high FSH to LH ratio (eFSH) on superovulation and reproductive performance in mares. A significance level of P < 0.05 was used for the data analyses. The treatment protocol included twice daily administration of 12.5 mg eFSH beginning at a follicular diameter of ≥20 or 25 mm. The treatment was stopped when a preovulatory-sized follicle was detected (≥35mm), and subsequently human chorionic gonadotropin (hCG) was administered to induce ovulation(s). The eFSH treatment significantly stimulated the ovaries of cycling and vernal transitional mares. This resulted in the development of multiple preovulatory-sized follicles, increased the number of ovulations, and enhanced donor embryo recovery rates. In mares which ovulated, approximately 70% of embryo recovery attempts resulted in the recovery of ≥1 embryo. However, incidences of ovulation failure and non-ovulatory follicles were significantly higher compared to control mares. Furthermore, there were significant variations in the superovulatory response to eFSH among cycling and vernal transitional mares in the same study, and among different studies, in terms of number of ovulations, number of embryos and embryo per ovulation rates. Administration of eFSH significantly modified reproductive tract variables (tone and edema) and serum concentrations of progesterone (P4) and estradiol-17β (E2) on the days that oocyte maturation, fertilization, and early embryonic development were expected to occur. The administration of eFSH was also significantly associated with lower quality scores in a proportion of embryos recovered, and lower than expected pregnancy rates in recipients which received an embryo recovered from eFSH-treated cycling donor mares as compared to embryos from non-stimulated control mares. Moreover, eFSH treatment did not significantly increase pregnancy rate per estrous cycle in mares intended to carry their own pregnancy; however, the incidence of twin pregnancy tended to increase. The effects of estrus synchronization regimens employed prior to eFSH treatment initiation were examined in cycling mares. A progesterone and estradiol regimen (P&E) was significantly more efficient than PGF2α administration in diestrus for ovulation synchrony among eFSH-treated mares, with ≥80% of mares ovulating within a 3 day period. The superovulatory outcomes (proportion of mares that ovulated, number of ovulations and embryo recovery), however, were significantly lower than those obtained with PGF2α administration. In vernal transitional mares, eFSH treatment resulted in a significantly higher number of preovulatory-sized follicles and a greater number of ovulations, compared to vernal transitional mares treated with deslorelin or porcine-FSH, or as compared to control mares. Most transitional mares (73% to 100%) ovulated after a mean of 5 days of eFSH treatment. These ovulations resulted in pregnancies and/or successful embryo recoveries. Following eFSH treatment in vernal transition, the first inter-ovulatory interval of the breeding season was significantly prolonged (>21 d) in about half of the mares. In summary, eFSH treatment significantly stimulated follicular growth and multiple ovulations in cycling mares and in vernal transitional mares. The treatment significantly increased reproductive efficiency of cycling mares in terms of embryo recovery rates, and in vernal transitional mares in terms of establishing pregnancies or recovering embryos early in the breeding season. However, the eFSH treatment significantly altered the hormonal environment (E2 and P4), and was associated with modifications in follicular growth, ovulation, and embryo parameters. These aspects should be considered in the development of superovulation protocols for mares in future studies