Ovarian response to porcine FSH in association with ablation-induced or spontaneous follicular wave development during the estrous cycle in crossbred and Brazilian Warmblood mares

The primary objective of this study was to examine the follicular and ovulatory responses following treatment with pFSH in association with ablation-induced or spontaneous follicular wave emergence or follicle deviation during diestrus in crossbred (Mangalarga × Arabian) and Brazilian Warmblood mares with a propensity for spontaneous multiple ovulations; secondary considerations were given to the collection of embryos. In Experiment 1, crossbred mares were administered (im) saline (control, n = 7) or pFSH (25 mg) when the largest follicle of the ablation-induced follicular wave reached ≥13 mm (n = 7) or ≥20 mm (n = 7) or, after pre-treatment ovulation (Day 0) on Day 6 (n = 7). In Experiment 2, crossbred mares were administered (im) saline (control, n = 10) or a larger dose of pFSH (50 mg, n = 7) when the largest follicle of the ablation-induced follicular wave reached ≥13 mm. In Experiment 3, Brazilian Warmblood mares were administered (im) saline (control, n = 7), pFSH (25 mg, n = 7 or 50 mg, n = 5) or EPE (12.5 mg, n = 7) as a positive control on Day 6. Ultrasonic technology was used to ablate all follicles ≥8 mm and to monitor follicular development and detect ovulation. Treatment with pFSH or EPE was done twice daily until the largest follicle reached ≥32 mm; thereafter, hCG (2500 IU) was administered (iv) when the largest follicle reached ≥35 mm. Artificial insemination was done 12 h after hCG and embryo collections were done 8 d after post-treatment ovulations. In Experiments 1 and 2, treatment of crossbred mares with pFSH post-ablation in association with the expected time of wave emergence or follicle deviation did not (P > 0.05) enhance the follicular or ovulatory responses or collection of embryos compared to controls. In Experiment 3, although the enhanced ovulatory response of mares to EPE at the expected time of spontaneous wave emergence was not different (P > 0.05) from controls, it was greater (P < 0.05) than the response to pFSH. In conclusion, the novelty of using follicle ablation prior to pFSH treatment at the time of wave emergence or follicle deviation did not enhance the follicular or ovulatory responses or collection of embryos to treatment in crossbred mares. In addition, the hypothesis that Brazilian Warmblood mares with a greater propensity for spontaneous multiple ovulations are as responsive to pFSH compared to EPE was not supported. Thus, the combined experimental results of the present study continue to support the general consensus that pFSH is relatively ineffective for follicular superstimulation/superovulation in mares.