Treatment with recombinant equine follicle stimulating hormone (reFSH) followed by recombinant equine luteinizing hormone (reLH) increases embryo recovery in superovulated mares

The dynamics of ovarian follicular development depend on a timely interaction of gonadotropins and gonadal feedback in the mare. The development and efficacy of genetically cloned recombinant equine gonadotropins (reFSH and reLH) increase follicular activity and induce ovulation, respectively, but an optimum embryo recovery regimen in superovulated mares has not been established. The objective of this study was to determine if treatment with reFSH followed by reLH would increase the embryo per ovulation ratio and the number of embryos recovered after superovulation in mares. Sixteen estrous cycling mares of light horse breeds (4–12 years) were randomly assigned to one of two groups: Group 1; reFSH (0.65 mg)/PBS (n = 8) and Group 2; reFSH (0.65 mg)/reLH (1.5 mg) (n = 8). On the day of a 22–25 mm follicle post-ovulation mares were injected IV twice daily with reFSH for 3 days (PGF2α given IM on the second day of treatment) and once per day thereafter until a follicle or cohort of follicles reached 29 mm after which either PBS or reLH was added and both groups injected IV twice daily until the presence of a 32 mm follicles, when reFSH was discontinued. Thereafter, mares were injected three times daily IV with only PBS or reLH until a majority of follicles reached 35–38 mm when treatment was discontinued. Mares were given hCG IV (2500 IU) to induce ovulation and bred. Embryo recovery was performed on day 8 day post-treatment ovulation. Daily jugular blood samples were collected from the time of first ovulation until 8 days post-treatment ovulation. Blood samples were analyzed for LH, FSH, estradiol, progesterone and inhibin by validated RIA. Duration of treatment to a ≥35 mm follicle(s) and number of ovulatory size follicles were similar between reFSH/reLH and reFSH/PBS treated mares. The number of ovulations was greater (P < 0.01) in the reFSH/reLH group, while the number of anovulatory follicles was less (P < 0.05) compared to the reFSH/PBS group. Number of total embryos recovered were greater in reFSH/reLH mares than in the reFSH/PBS mares (P ≤ 0.01). The embryo per ovulation ratio tended to be greater (P = 0.07) in the reFSH/reLH mares. Circulating concentrations of estradiol, inhibin, LH and progesterone were not statistically different between groups. Plasma concentrations of FSH were less (P < 0.01) in the reFSH/reLH treated mares on days 0, 1, 4, 6, 7 and 8 post-treatment ovulation. In summary, reFSH with the addition of reLH, which is critical for final follicular and oocyte maturation, was effective in increasing the number of ovulations and embryos recovered, as well as reduce the number of anovulatory follicles, making this a more viable option than treatment with reFSH alone. Further evaluation is needed to determine the dose and regimen of reFSH/reLH to significantly increase the embryo per ovulation ratio.