Caracterização do desenvolvimento reprodutivo em fêmeas Nelore (Bos taurus indicus) em dois momentos da fase pré-puberal

Abstract

Brazil has the largest commercial herd in the world, being mostly composed of Nelore animals. In addition, it is one of the largest producers of in vitro embryos in the world, technology that allows to accelerate the herds’ genetic gain. However, the Zebu cattle Nelore usually shows later puberty when compared to Taurines, that causes genetic improvement delays in Zebu. In this context, the possibility of including calves as oocyte donors for in vitro embryo production programs (IVEP), could be an attractive alternative, aiming to reduce the interval between generations and accelerate the genetic gain of herds, contributing to increase the efficiency and sustainability (economic, social and environmental) on milk and meat production systems. However, it is known that calves’ oocytes are considered less competent to generate blastocysts and establish pregnancies than those obtained from adult females. In addition, it is observed that most of the studies addressing this topic have been carried out mainly with Taurine cattle, thus, further studies on the endocrine and reproductive physiology of Zebu calves could be important on this purpose. For this reason, the present study aims to evaluate the hormonal concentrations of FSH / LH, the correlation among ovarian and uterine characteristics with the rump development and its geometry changes, the oocytes morphological and molecular characteristics and the in vitro embryo production rates in 2 to 5 and 8 to 11 months old Nelore females. Thus, in addition to better understanding of the reproductive development, it would be possible to contribute with information to subsidize decisions about the use of this animal category in this phase, donors’ hormonal protocols and alternative culture media changes for IVEP from prepubertal oocytes.