Exposição de progesterona previamente ao protocolo de IATF e seus efeitos na fertilidade de vacas de corte em anestro pós-parto

Abstract

The objective of the study was to evaluate the effect of administering 150mg of long-acting injectable progesterone (P4i) prior to the TAI protocol on the fertility and follicular dynamics of Bos indicus and Bos taurus cows in anestrus, and on the uterine diameter and expression of receptors in endometrial cells of Bos indicus cows in postpartum anestrus. In addition, the effect of previous exposure to progesterone replacing eCG in TAI protocols was evaluated. In study 1, the animals were divided into 3 groups (Control, P4 and P4GnRH). Cows in the P4 and P4GnRH groups received P4i on D-10. On D0, cows from all groups received a TAI protocol. In this moment, 10μg of buserelin was administered to cows in the P4GnRH group. There was a difference between groups regarding DF on D0 (P=0.001), on D8 (P=0.05) and on P/AI (P=0.01). In study 2, P4i prior to the TAI protocol was evaluated in lactating Bos taurus cows. On D-10, the cows were divided into Control and P4i groups. There was a higher DF in D0 (P=0.01) and D8 (P=0.08), in addition to a higher P/AI in cows in the P4i group (P= 0.03). In study 3, the effect of replacing eCG with P4i prior to the TAI protocol in suckled Nellore cows was evaluated. On D-10, cows were allocated in a 2x2 factorial arrangement to receive or not receive 150mg of P4i on D-10 and receive or not receive 300UI eCG on D8. DF was higher at D0 (P<0.01) and at D8 (P<0.01) in cows that received P4i. Follicular growth rates (P<0.01) and P/AI (P<0.01) were higher in cows receiving eCG. In addition, there was a difference between the groups in the diameter of the DF on D10 (P=0.04). In study 4, the effect of prior administration of P4i to the TAI protocol on uterine diameter and expression of PGR, ESR1, ESR2 and OXTR in endometrial cells on D0 and D10 of Bos indicus cows in postpartum anestrus was evaluated. On D-10 the cows were divided into Control and P4i groups. Uterine diameter on D0 (P=0.10) and D10 (P=0.07) tended to be larger in the P4i group. OXTR expression tended to be higher in cows in the P4i group (P=0.08). In addition, the difference in ESR1 expression from D-10 to D0, a greater increase in expression was observed in cows from the P4i group (P>0.05). Furthermore, it was observed that the difference in ESR2 expression from D-10 to D10 was lower in cows in the P4i group (P=0.05). It is concluded that the administration of long-acting progesterone 10 days prior to the ovulation synchronization protocol increases the follicular diameter on D0 and D8 and increases the fertility of beef cows. Furthermore, prior exposure increased uterine diameter and modified expression of ESR1, ESR2 and OXTR in the ovulation synchronization protocol. However, prior exposure to progesterone is not an alternative to replacing eCG in the FTAI protocol.