368 OOCYTE ASPIRATION FROM TRANSITIONAL AND CYCLING MARES TREATED WITH eFSH

A major obstacle in studying equine oocyte maturation is a source of oocytes. The aim of this study was to determine if oocyte recovery following transvaginal ultrasound-guided aspirations could be improved by using eFSH. Fourteen mares ranging from 3 to 16 years of age were used as oocyte donors during the transitional (March to April) and cycling (May to June) seasons. Each follicle was aspirated with a 12-gauge double-lumen needle using a pressure of 150 mmHg and then flushed eight times using PBS supplemented with 10 U/mL heparin and 0.05% BSA. Large follicles (>20 mm) were aspirated first, followed by small follicles (10–20 mm). The first aspiration in each season was used to deplete the follicular pool of all follicles >10 mm; these data were not considered. Following this initial aspiration, mares were subjected to four rounds of aspirations every 10 to 11 days. In each round during the transitional season, half the mares received 12.5 mg eFSH (Bioniche Animal Health, Belleville, Ontario, Canada) once daily for four days prior to aspiration. For each round during the cycling season, half the mares received 12.5 mg eFSH twice daily for three days prior to aspiration. In each replicate, mares were alternated from treated to control groups during both seasons. Oocyte recovery and superstimulatory responses were analyzed using the GLM procedure of SAS (SAS Institute, Inc., Cary, NC, USA). During both the transitional and the cycling season, treatment with eFSH did not have a significant effect (P > 0.1) on the number of small or large follicles present at the time of aspiration (Table 1). For both seasons and size classes, the number of follicles varied by mare (P < 0.02). Oocyte recovery from small follicles during the transitional season improved during the later two rounds of aspiration (0.58 vs. 1.49; P < 0.01) and was also affected by mare (P = 0.06). During the cycling season, recovery of oocytes from both small and large follicles varied by mare (P < 0.05). Treatment with eFSH increased the number of oocytes recovered from large follicles in cycling mares (P < 0.05). This study indicates that responses to short-term eFSH treatment for the purpose of oocyte recovery vary greatly by mare. While treatment with eFSH did not increase the number of follicles available for aspiration (P > 0.1), it did increase the number of oocytes recovered from large follicles during the cycling season. Table 1. Oocyte recovery and superstimulatory response of mares treated with eFSH