261 DIFFERENT TRANSVAGINAL OVUM PICK-UP STRATEGIES TO OPTIMIZE THE OOCYTE RETRIEVAL AND EMBRYO PRODUCTION OVER A FIXED PERIOD OF TIME

The objective of this study was to compare the efficacy of different oocyte retrieval schemes over a period of 10 weeks. Fifteen multiparous Angus cows were randomly assigned (n = 3/group) to the following groups: 1) OPU once/week (7-day interval), 2) OPU twice/week (3- and 4-day interval, alternately), 3) Dominant follicle removal (DFR) + OPU once/week. DFR followed by OPU 72 h later, 4) DFR + FSH + OPU once/week. DFR followed 36 h later by FSH (Folltropin, Bioniche, Belleville, Ontario, Canada) (120 mg s.c. and 80 mg i.m. administered simultaneously) followed by OPU 48 h later, 5) FSH + OPU twice/week. FSH followed by OPU1 30 h later and OPU2 96 h after OPU1. The interval between OPU2 and next FSH was approximately 42 h. The follicles were aspirated using an Aloka ultrasound scanner (Wallingford, CT, USA) and a 5-MHz probe. The COCs were selected based on morphology and matured in TCM-199, supplemented with 10% FCS, 0.01 units mL-1 bFSH, 0.01 units mL-1 bLH and antibiotics. Fertilization (Day 0) was carried out with TALP-FERT medium containing capacitation factors. Frozen semen from the same bull was used (1 × 106 mL-1) throughout. After 18 h the presumptive zygotes were cultured in SOF with 5% FCS (Holm P et al., 1999 Theriogenology 52, 683–700). The embryos were evaluated based on IETS guidelines (Grades 1 and 2 selected). The data were analyzed by chi-square test and ANOVA. In all parameters, the DFR followed by FSH and subsequent OPU once/week protocol gave the best results on a per-cow-per-week as well as total (3 cows over 10 weeks) basis. Though OPU was done only once/week, this group produced more total oocytes (303) than groups where OPU was done twice/week, either with FSH (286) or without FSH (229) and also produced more total embryos on Day 8 (71 blastocysts, 23.4% of oocytes cultured) than the latter two groups (64, 22.4% and 49, 21.4%, respectively). Among the nonstimulated groups, the OPU twice/week group had more total oocytes (236) than groups with OPU once/week, either without DFR (137) or with preceding DFR (160). However, a preceding DFR seemed to have a positive effect on oocyte quality as this group had a better embryo development rate (26.9%), producing more total embryos (42). In comparison, OPU twice/week produced total 49 embryos (21.4%) and OPU once/week produced 26 (19.4%). In conclusion, DFR coupled with single-shot FSH administration can be used effectively over a period of at least 10 consecutive weeks and can increase (P < 0.05) the oocyte yield by two-fold and embryo production following IVF by two and half-fold, as compared to routine OPU-IVF done once a week. Table 1 Per cow per week performance

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