Avaliação in vitro e in vivo da fertilidade do sêmen bovino em programas de IATF

Abstract

Artificial insemination (AI) is mainly applied to increase the productivity and profitability of cattle herds. Fixed-time AI programs (FTAI) increase the use of AI and the reproductive efficiency of herds. However, the success of FTAI programs is dependent on the semen quality, because higher conception rates can be obtained when bulls with good fertility histories are used during the breeding season. This thesis is presented in the form of two manuscripts. The aim of the manuscript 1 was to evaluate the conception rate of Bos taurus taurus females submitted to FTAI with different sets of commercial bovine semen in addition to investigate the association between conception rate and demonstration of estrous and body condition score (BCS) of taurine females. The aim of the manuscript 2 was to evaluate the influence of the moment of FTAI (48 or 54 h after the progesterone device removal) on the conception rate of high and low fertility bulls. In addition, the association between spermatic kinetics and functionality, after thermoresistance test and sperm selection, with field fertility of bulls previously classified as having high or low fertility was also investigated. The data obtained in the manuscript 1 demonstrated that there is individual variation in fertility of bulls used in FTAI programs and a difference in conception rate was observed among different sets of semen from the same bull. In addition, it was shown that the demonstration of estrus and BCS are essential data that must be carefully analyzed in the FTAI programs, because low conception rates are observed in females not in estrus or in those with low BCS. The data obtained in the manuscript 2 emphasized that the conception rate was similar between low and high fertility bulls when the insemination was delayed to 54 h after removal of progesterone device in FTAI programs, i.e. nearest to ovulation. In addition, low fertility bulls present lower quantitative parameters of sperm movement (VCL, VSL and VAP), determined by the computerized method after thermoresistance tests, than high fertility bulls.