286 ASSESSMENT OF NUCLEAR AND CYTOPLASMATIC MATURATION IN VITRO OF OOCYTES COLLECTED AT DIFFERENT STAGES OF FOLLICULAR WAVE FROM NELORE COWS (BOS TAURUS INDICUS)

Abstract

The objective of experiment 1 was to evaluate the influence of follicular wave moment on the quality and number of recovered oocytes through ovum pick-up (OPU), as well as blastocyst rate, in Nelore cows. Two hypotheses were tested: (1) the number of recovered viable COC would be higher at Days 3 and 5 than at Days 7 and 9; (2) the COC aspirated at the beginning of the follicular wave (Day 3 or Day 5) would be more competent and would produce more blastocysts than COC obtained at the end of the wave (Day 7 and Day 9), because these would be in a certain degree of advanced atresia. Cows (n = 10) received 2 mL of estradiol benzoate (Estrogin®), an auricular progestagen implant (Crestar®) for 7 days, and 2 mL of PGF2 analog (Preloban®) at the moment of implant retrieval. After 24 h animals were submitted to aspiration of the dominant follicle (ADF), this moment being considered Day 0. After ADF the donors were submitted to OPU on Days 3, 5, 7, and 9 (groups D3, D5, D7, and D9, respectively) of the new follicular wave. Each animal was submitted to all treatments. In each phase the protocol began with a 2-day interval from the group D9, D7, D5, and D3. Recovered COC went to IVM, IVF, and IVC in the same session of IVP. Statistical analysis were performed with SAS software (SAS Institute, Cary, NC, USA), using ANOVA at a 5% level of significance. There was no difference in the total number of follicles visualized at the moment of OPU among groups (D3:195, D5:189, D7:161, D9:151) or in the recovery rate (77.94; 78.30; 72.04; 73.50) and number of recovered total structures (152, 148, 116, 111). There was no difference in the total number of viable COC (133, 137, 103, 97) or in cleavage rate of COC in the 4 groups (79.69; 83.45; 71.84; 76.28). The total number and the blastocyst rates were higher in groups D3 and D5 (66, 49%, and 62, 45.25%) than in groups D7 and D9 (34, 33%, and 35, 36.08%). Statistical analysis was performed with the chi-square test, with a significance level of 5%. In experiment 2 nuclear and cytoplasmatic maturation were evaluated in COC recovered at Days 4 and 8 regarding nuclear maturation (progression to metaphase II stage) and cortical granule migration, respectively. The hypothesis tested was that COCs recovered at the beginning of the follicular wave would have a higher competence and therefore higher maturation rate compared with those the aspirated at the end. There was no difference in the number of viable COC (78 v. 97), percentages of nuclear maturation (74.35 v. 53.6), and cytoplasmatic maturation (48.71 v. 30.92). The results of the 2 experiments demonstrated that the beginning wave (Days 3 to 5) is the most appropriate moment for obtaining oocytes destined for IVP because of the greater oocyte competence and consequently, larger number and increased blastocyst production rates. Moreover, the results obtained in experiment 2 indicate that the low rate of cytoplasmic maturation can be a major limiting factor of IVP in Nelore cows. FAPESP.