O uso do protocolo de sincronização da ovulação CO-Synch 5 dias modificado aumenta a taxa de prenhez de novilhas leiteiras?

Abstract

Fixed-time artificial insemination (TAI) is the most widely used reproductive biotechnique in cattle herds in Brazil. Since the emergence of this biotechnique, different protocols have been developed aiming to improve pregnancy rates. Artificial insemination (AI) in heifers is a challenge. Thus, protocols based on gonadotropin-releasing hormones (GnRH) or progesterone (P4) are tested to increase the pregnancy rate of heifers. Studies indicate that the use of the 5-day CO-Synch protocol resulted in pregnancy rates of 50.7% when used in AI in this group of animals. The aim of this study was to evaluate the effect of modified 5-day CO-Synch protocol on the TAI pregnancy rate in new crossbred dairy cows. 386 heifers were evaluated from a commercial farm, located in the city of Guimarânia, MG. They were divided into 3 groups: Modified 5-day CO-Synch Group (n = 32): received treatment with a dose of 1.0 mL of GnRH on D0, additionally with the P4 slow-release intravaginal device input, which was removed after 5 days and administration of 2.0 mL of Prostaglandin F2α (PGF2α), with a second dose of PGF2α on D6 and application of 0.5 mL of estradiol cypionate (ECP), followed by AI after 48 hours; 9-day Protocol Group based on P4 and BE (n = 67); and Group estrus detection and conventional AI (n= 287). Pregnancy diagnosis was performed by transrectal ultrasound 28 to 40 days after AI. The data were analyzed using logistic regression in the MINITAB Program, with the group effect being included in the model. The pregnancy rate for the modified 5-day CO-Synch Group was 53.13%, being (P = 0.032) lower than estrus detection and conventional AI Group (71.78%), but similar to that of the 9-day Protocol Group (68.66%). It is concluded that the modified 5-day CO-Synch protocol used in the present study was proven to have a lower pregnancy rate when compared to new inseminates after detection of natural estrus.