Características genéticas e fisiológicas envolvidas na caracterização das diferentes CFAs em novilhas das raças Nelore e F1 Nelore x Angus

Abstract

Despite the great advances in the use of reproductive biotechnology in cattle herds in Brazil, it is clear that the production system needs to be optimized to improve efficiency and profitability. To make the system more profitable and sustainable, many studies were carried out. Regarding reproductive management, those who have dedicated themselves to better understanding the anal follicle count (AFC) stand out. AFC has been associated with fertility in herds of Bos taurus and Bos indicus breeds, however there is a divergence between the results for these breeds and several mechanisms still need to be understood so that the selection of animals, based on this characteristic, is efficient and can be applied to all herds. In this sense, the present work aims to evaluate the genetic and physiological characteristics involved in the relationship between AFC and the fertility of Nelore (Bos indicus) and F1 Nelore x Angus (Bos indicus x Bos taurus) heifers, in FTAI programs. To this end, this thesis was developed in two parts to meet the objectives of evaluating the relationship between AFC: with the serum and follicular fluid hormonal profile (IGF-1, E2, and P4) with the reproductive performance of precocious Nelore heifers in FTAI programs (article 1) and the relationship between AFC and FTAI performance, oocyte and carcass quality; as well as gene expression, through RNA-seq, of oocytes from precocious and F1 Nelore x Angus heifers (article 2) For this, 70 Nelore heifers and 140 F1 Nelore x Angus heifers belonging to commercial properties that work with breeding were used genetics and sexual precocity of bovine females, located in the state of Mato Grosso do Sul. The identification of AFC was carried out by counting individual follicles visualized by transrectal ultrasound. The division of the AFC groups in both articles was based on knowledge of the mean AFC and the use of ± 1 standard deviation of the sample, as has already been pointed out in articles involving AFC, since this characteristic can be changed between herds Thus, in article 1 the low, medium and high AFC groups contained ≤14, 15 to 30 and ≥31 follicles, respectively, while in article 2 the ranges were ≤13, 14 to 30 and ≥31 follicles. In both studies, no differences were found in conception rates between the AFC groups. In Article 1, IGF-I on D10 and DG was higher for the high AFC group, and IGF-I concentrations did not influence pregnancy rates. In article 2, there was no relationship between AFC and carcass ultrasound data (AOL, EG, and EGP), nor with ovarian ultrasound and morphology of ovarian structures, except for ovary size, which was larger for the ovary high AFC group. Regarding gene expression, 93.75% of the differently expressed genes were effectively regulated in the low AFC group, which is related to the causes of infertility. Therefore, we concluded that AFC was not related to the sexual precocity of Nelore and Nelore X Angus heifers, when we used the first pregnancy and FTAI as a parameter.