229 INFLUENCE OF HIGH OR LOW INTAKE OF DRY MATTER AND ENERGY ON IN VIVO PRODUCTION OF BOVINE EMBRYOS

Abstract

The aim of this study was to evaluate the influence of high or low dry matter (DM) intake and/or energy on embryo quality and production in vivo. Nonlactating Nelore cows (n = 32, 4 to 10 years old) weighing 489.5 ± 11.3 kg and with a body condition score of 3.25 (1 to 5) were used. After 15 days on the adaptation diet, cows were blocked by initial body weight (BW) and randomly divided in 4 experimental groups. The maintenance group (M) received a diet to provide 1.2% of DM/kg of BW. The restriction group (0.7M) received the equivalent of 70% of the group M diet (0.84% of DM per kg of BW). The high intake group (1.5M) received the equivalent of 150% of the M group (1.8% of DM/kg of BW). The energy group (E) received a diet with a DM similar to the M group but with an energy level equivalent to the 1.5 M group. All cows were submitted to aspiration of follicles >2 mm for ovum pick-up (OPU). Recovered oocytes were used in another experiment. The embryo donors received an intravaginal device (IVD) of progesterone release (Sincrogest^®, Ouro Fino, Ribeirão Preto, Brazil), soon after OPU. Two days after OPU, the cows received 8 decreasing doses of FSH (100 mg, IM, Folltropin-V^®, Bioniche Animal Health, Belleville, Ontario, Canada) and concomitant with the fifth and sixth treatments of FSH, PGF_2α (500 μg each, IM, cloprostenol, Sincrocio^®, Ouro Fino) was administered. The IVD was removed at the time of the last FSH injection. Twelve hours after IVD removal ovulation was induced with GnRH (0.01 mg, IM, Buserelin acetate, Sincroforte^®, Ouro Fino). Cows were inseminated 12 and 24 h later. Embryo collection was performed 7 or 8 days after GnRH injection. The cows were offered all diets in a crossover design study. There were 4 sessions of embryos flushing, each 42 days apart. Data were analysed by PROC GLIMMIX of SAS (SAS Institute Inc., Cary, NC, USA) and the results are presented as least-squares means ± SE, always following the order of treatments 0.7 M, M, 1.5 M and E. There were differences in the superstimulatory response (12.6 ± 1.4^b; 14.6 ± 1.6^a; 13.6 ± 1.5^ab; and 11.0 ± 1.2^c follicles >6 mm; P < 0.01) and superovulatory response (9.8 ± 1.3^ab; 11.0 ± 1.4^a; 10.2 ± 1.3^a; and 8.6 ± 1.3^b CL; P < 0.01) among groups. Despite the lower responses observed especially in the high-energy group, no difference among groups was observed for total embryos/ova (4.5 ± 0.7; 5.0 ± 0.8; 5.0 ± 0.8; and 4.7 ± 0.7; P = 0.60), viable embryos (2.0 ± 0.4; 2.3 ± 0.5; 2.6 ± 0.6; and 2.2 ± 0.5; P = 0.40), or freezable embryos (1.7 ± 0.4; 2.0 ± 0.4; 2.1 ± 0.5; and 1.9 ± 0.4; P = 0.60). There was also no difference among groups for fertilization rate (75.8 ± 9.6; 82.3 ± 8.0; 87.8 ± 6.6; and 81.1 ± 8.4%; P = 0.71) and percentage of viable embryos (54.5 ± 10.8; 50.8 ± 10.6; 50.5 ± 10.9; and 54.4 ± 10.7%; P = 0.98). In conclusion, in contrast to our initial hypothesis, a period of 42 days under high feed/energy intake in nonlactating zebu cows apparently did not compromise in vivo embryo production. This may be because cows had a moderate body condition score or because the feeding period was not long enough to compromise oocyte/embryo quality.

Financial support from FAPESP and CNPq is acknowledged.