Efeito da progesterona e estrogênio nas características foliculares e lúteas em protocolos de sincronização e ressincronização com aitf em vacas bos taurus taurus / bos taurus indicus

Abstract

Fixed-time artificial insemination is a tool of reproductive biotechnology that improves the herd's genetics to obtain more productive animals. The objective of this work was to evaluate the associations between the occurrence of estrus after synchronization and ovulation protocols and follicular diameter at the time of fixed-time artificial insemination (TAI) on ovarian responses and pregnancy rate after TAI in females Bos taurus taurus/ Bos taurus indicus. Thus, possible practical implications of using this information to improve TAI programs in lactating mixed-breed females were evaluated. In the first chapter, the associations between follicular diameter at the time of TAI and the occurrence of estrus between the end of the synchronization protocol and the moment of TAI were evaluated on the ovarian response and the conception rate after TAI. It was observed that the increase in follicular diameter at the time of TAI increases the conception rate after TAI and that the occurrence of estrus after the synchronization protocol is associated with better ovarian responses and a better conception rate after TAI. Therefore, strategies to improve the occurrence of estrus and follicular diameter at the time of TAI are essential for the success of ovulation synchronization programs for TAI of Bos taurus taurus/Bos taurus indicus females, and such criteria can be used in the selection of females to receive high genetic quality semen. The second chapter reports on four studies in which the associations between the use of progesterone and estrogen and their effect on luteal characteristics in resynchronization protocols using TAI were evaluated, as well as the determination of the pregnancy rate in Bos taurus taurus/Bos taurus indicus cows during the resynchronization protocol. The results indicate that it is possible to obtain higher conception rates after ovulation resynchronization in crossbred cattle but without estradiol or with low doses.