Estratégias Anti-Luteínicas sobre a Fertilidade de Novilhas de Corte.

Abstract

This study was carried out to evaluate the effects of progesterone (P4) supplementation after fixed-time artificial insemination (AI) through two different routes of administration (oral and intramuscular) on pregnancy rate of Nellore heifers. Forty five Nellore heifers were used averaging months (30 ± 2.08) of age, (330 ± 0.707) kg BW and 2.5 BCS (five-point scale) at the beginning of the experiment. Heifers were randomly assigned to three experimental groups of fifteen animals each and maintained on an extensive grazing system (Andropogon pasture) with mineral supplementation and water ad libitum. Experimental groups (treatments) included: group 1 (control group) (no exogenous P4 administration (G1)); group 2: intramuscular (IM) administrationof 1.0 mL P4 (Sincrogest injectable; OuroFino) on day 4 afterAI (G2); and group 3: supplementation of 2.28 mg/animal/day P4 (melengestrol acetate MGA; Zoetis), starting 4 days afterAI and remaining until day9 (d 4 – d 9). Progesterone (MGA) was incorporated to the mineral-protein energy supplement (Phósverão–Acabamento–Matsuda) and offered to the animals (G3), daily in the morning. All animals were submitted to the following fixed-time AI protocol: On d zero, an ear implant of P4 was placed (Crestar, MSD) and 2 mg estradiol benzoate (EB, Fertilcare Sincronização, MSD) was administered IM. Eight days later (d 8), the ear implant was removed and 2 ml of synthetic prostaglandin (Ciosin, MSD), 1.5 ml ecG (Folligon 5000 UI, MSD) and 1 ml estradiol cypionate (Fertilcare Ovulação, MSD) were administrated IM. On d 10 of the protocol, AI was performed and the diameter of preovulatory follicles were measured by transrectal ultrasonography. Pregnancy diagnosis was performed thirty-five days after-AI. Estrus expression was evaluated by tail-painting of each cow on d 8 of the protocol, and evaluating the presence of paint at AI. Statistical analyses were performed using the ONE PARWAY procedure of SAS. The Kruskal-Wallis test was used to check for significant differences among treatments. There was no significative difference on pregnancy rate among experimental groups. Supplementation of P4 from d 4 to d 9 after AI, through oral administration, resulted in numerically higher percentage of pregnantanimals (G3) compared to IMP4 administration (G2) and no P4 administration (G3). Both diameter of dominant follicle and the estrus expression showed no positive effect on conception rate in Nellore heifers during the dry season.