293 EFFECT OF FOLLICULAR WAVE SYNCHRONIZATION ON IN VITRO EMBRYO PRODUCTION IN COWS

In order to achieve the ideal time of ovum pickup (OPU) for in vitro embryo production (IVP) in cows regarding number and quality of oocytes recovered, this study investigated the effect of synchronization of wave emergence with estradiol benzoate (EB) injected 7 days prior to follicular aspiration. In a Latin square design, 12 crossbred beef cows were randomly divided into three groups, with three replicates each. Cows were synchronized with a norgestomet ear implant for 7 days followed by an i.m. prostuglandin F2� (PGF2�) injection and aspiration of all ovarian follicles larger than 3 mm in diameter. After that, follicles from cows in group 2X were aspirated twice a week with 4- and 3-day intervals, and follicles from groups 1X and 1X-EB were aspirated once a week. Cows from group 1X-EB also received an im injection of 2 mg of EB immediately after OPU. Throughout the study cows were kept with an ear norgestomet implant that was replaced every 2 weeks. Ultrasound evaluations of numbers of follicles greater than 3 mm in diameter and size of the largest follicle at the time of OPU were performed. Recovered oocytes were evaluated for quality, and the viable ones (Grades I, II, and III) were in vitro-fertilized on Day 0. Cleavage rate was evaluated on Day 2 and blastocyst production on Day 7. Continuous variables were compared by ANOVA and binomial data were compared by chi-square. For the 2X group, only data from the OPU performed 3 days after the last OPU were used for analysis. Results are presented as percentages or mean � SEM. Size of the largest follicle was greater (P < 0.05) in 1X coes (12.9 � 0.2 mm) than in 1X-EB cows (11.1 � 0.3 mm), which was greater than in 2X (9.6 � 0.4 mm) cows. The 1X cows had more follicles at OPU than 2X cows (17.5 � 0.7 vs. 14.1 � 0.9), whereas the 1X-EB group (15.9 � 0.7) was intermediate and not different from the others. There was no difference in the mean number of recovered oocytes among 2X (9.6 � 0.6), 1X (12.7 � 0.8) and 1X-EB (12.3 � 1.0) cows, and the mean number of viable oocytes among groups (5.8 � 0.5, 7.3 � 0.5, and 7.0 � 0.6) for 2X, 1X, and 1X-EB cows, respectively). The rate of viable oocytes was also similar among groups [58.8% (191/325) for 2X, 58.4% (267/457) for 1X, and 57.2% (231/404) for 1X-EB cows]. Cleavage [68.6% (131/191), 65.2% (174/267), and 68.4% (158/231)] and blastocyst [38.7% (74/191), 43.8% (117/267), and 44.2% (102/231)] rates were also not different among 2X, 1X, and 1X-EB groups, respectively. Although the use of 2 mg of EB in association with a norgestomet implant 7 days prior to OPU altered the follicular wave profile, it was not enough to improve number and quality of the oocytes recovered. Moreover, this study failed to demonstrate a positive effect of OPU earlier after wave emergence, when the effect of dominance should be less pronounced, on IVP in cows. The first author was supported by the fellowship 141077/2004-2 of CNPq, Brazil.