387 EFFECT OF NUMBER OF INSEMINATIONS ON EMBRYO PRODUCTION IN SUPERSTIMULATED NELORE (BOS INDICUS) COWS SUBJECTED TO FIXED-TIME ARTIFICIAL INSEMINATION

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In embryo transfer programs, 2 inseminations per superstimulated donor are usually recommended. Based on studies of follicular dynamics in Bos indicus donors (Baruselli et al. 2006 Theriogenology 65, 77–88), we tested the hypothesis that a single fixed-time AI (FTAI) at 16 h after pituitary luteinizing hormone (pLH) treatment is as efficacious as 2 FTAI at 12 and 24 h after the pLH treatment. Suckling Nelore cows (n = 10), 60 � 12 days postpartum, were equally distributed in 2 experimental groups: G-1TAI vs. G-2TAI, in a crossover design. All animals received an intravaginal progesterone device (DIB; Syntex S.A., Buenos Aires, Argentina) and 2 mg of estradiol benzoate (IM, Ric Be; Syntex) at random stages of the estrous cycle (Day 0). Superstimulatory treatments started on Day 4 with pFSH (133 mg; Folltropin-V; Bioniche Animal Health Canada, Inc., Belleville, Ontario, Canada) in 8 decreasing doses, given IM 12 h apart. On Day 6, all cows received 2 (AM and PM) treatments of 0.15 mg of d-cloprostenol (Prolise; Syntex). The DIB devices were removed 36 h after the first PGF2� injection. The pLH treatment (25 mg IM; Lutropin-V; Bioniche) was given 48 h after the first PGF2� treatment (12 h after the last pFSH treatment). In the G-2TAI group, all cows received 2 inseminations (12 and 24 h after the pLH). Cows in the G-1TAI group received a single insemination (16 h after the pLH). All inseminations were done with the same batch of semen from a single bull. Ultrasound examinations (PIE Medical Scanner 200; Pie Medical Equipment, Maastricht, The Netherlands) were performed every 12 h from 0 to 72 h after pLH treatment to evaluate the number of ovulatory follicles (<8 mm), the ovulation rate, and the time of ovulation. Variables were analyzed by ANOVA and chi-square test. The homogeneity of the variances (distribution of ovulations) was analyzed by Bartlett's test. Conclusions were based on a 5% level of significance. The results for G-1TAI and G-2TAI were, respectively: number of follicles >8 mm at the time of pLH administration (16.2 � 1.4 vs. 14.8 � 1.2; P > 0.05), ovulation rate (63.8 � 3.8% vs. 64.2 � 4.3%; P > 0.05), interval from the first to the last ovulation (32.4 � 1.8 vs. 33.6 � 1.6 h; P > 0.05), total ova/embryos (8.2 � 0.9 vs. 7.2 � 0.8; P > 0.05), Grade 1 embryos (2.0 � 0.5 vs. 2.3 � 0.4; P > 0.05), transferable embryos (Grades 1, 2, and 3) (4.3 � 0.7 vs. 4.2 � 0.6; P > 0.05), freezable embryos (Grades 1 and 2) (2.9 � 0.6 vs. 2.8 � 0.4; P > 0.05), unfertilized ova (0.6 � 0.2 vs. 0.8 � 0.2; P > 0.05), and degenerated embryos (3.3 � 0.9 vs. 2.2 � 0.3; P > 0.05). These results suggest no significant differences in embryo production between superstimulated Nelore donors inseminated once or twice by fixed time following administration of pLH. This work was supported by Tecnopec, Brazil.