Indução a puberdade de novilhas de corte Bos Taurus com progesterona injetável e prostaglandina

Abstract

Heifers that have the capacity to be cycling at the beginning of the reproductive season are in anestrus, which is a limiting factor for reproduction. Causing delay in the reproductive efficiency and profitability of the herd. Different puberty induction programs have been used to minimize this deficiency, enhancing the productivity of commercial herds and producing an extra reproductive cycle in females' lives. Thus, the objective of this work was to evaluate the effect of inducing puberty with injectable progesterone (iP4) and its association with prostaglandin (PG) on the fertility of taurine heifers aged between 16 and 20 months submitted to FTAI protocols. The experiment was divided into two phases, in three commercial farms in the West Frontier of the state of Rio Grande do Sul. In experiment I, 289 prepubertal heifers were used, evaluated for weight, body condition score (BCS), reproductive tract score (RTS), cyclicity (presence or absence of CL) on days D-50, D-26 and D0, pregnancy rate and pregnancy loss on D30 and D60. They were divided into: negative control group (C-) composed of untreated heifers, and four treatment groups: T-50 received an application of 150mg of P4 (IM) (injectable Sincrogest®, OuroFino) on D-50; T-26 one application of 150mg of P4 (IM) on D-26, P4P4 two doses of P4 on D-50 and D-26 (IM) and the P4PG group one dose of P4 (IM) on D-50 and 12 .5 mg of PG (IM) (Sincrocio®, OuroFino) on D-26. On D0, heifers started the FTAI protocol and were inseminated on D10. Pregnancy diagnosis was performed 30 and 60 days after AI and the pregnancy loss rate was calculated. In experiment II, 12 prepubertal heifers were distributed into four treatment groups: T-50, T-26, P4P4 and P4PG as described in experiment I. The first day of the puberty induction protocol was designated as D-50. The heifers were evaluated every two days for: weight, BCS, RTS and cyclicity, the evaluations lasted 52 days. Blood samples for serum progesterone assessment were collected for 12 consecutive days after each treatment (D-50 and D-26). For the statistical analysis, GLIMMIX from SAS was used and the variables compared by the Tukey test (P<0.05). The uterine diameter of the P4P4 and T26 groups were similar to each other and showed a better diameter (16.04±0.34; 16.63±0.32). The C- group (15.2±0.3) was equal to the T-50 (15.8±0.4) and P4PG (15.7±0.4) groups. The cyclicity rate on D0 was lowest in the C- group (33.9%), and the highest in the P4P4 group (62.7%). The estrus rate on the day of AI was lower in the C- group (53.6%) and higher in the T-26 (84.0%) and P4P4 (83.0%) groups. The pregnancy rate at 30 days was lower in the C- (50.0%), T-26 (49.0%) and P4PG (48.0%) groups and higher in the T-50 and P4P4 groups (55.7%; 67.8%). In the DG at 60 days, the C- and T-26 groups had a lower mean (35.7%; 37.3%) and the T-50 and P4P4 groups (49.2%; 59.3%) had a higher pregnancy rate. There was no difference in pregnancy loss between treated and control groups (P=0.43), as well as there was no difference between follicle size at AI (P=1.00) and cyclicity rate at D30 (P=0.24). However, heifers with uterine diameter >20mm had better means of estrus rate at AI (81.2%), pregnancy at 30 days (68.7%) and 60 days (68.7%) and lower pregnancy loss (0.0%). Thus, the induction protocol with P4i accelerated the reproductive development of prepubertal heifers. When used 50 and/or 25 days before the start of the TAI protocol, it was able to stimulate uterine development, increase the AI cyclicity rate and increase the pregnancy rate.