Effect of the Estrus Expression on Follicular and Luteal Morphofunctional Characteristics and Fertility in Bos indicus females Synchronized for FTAI
Authors: Menezes Artur Azevedo , Batista Lucas Andrê Silva , Sousa Aldo Barbosa , Loiola Marcus Vinícius Galvão , Bittencourt Rodrigo Freitas , Ribeiro Filho Antonio de Lisboa , Rodrigues Alexandra Soares 
Published: June 2021

Background: Recent studies have been conducted with the aim of improving the fertility rates in the FTAI programs in beef females. The observation of the estrus expression constitutes an important indicator of fertility in zebu females. Therefore, this work has as an objective to evaluate the impact of the estrus expression on the follicular, luteal and fertility morphofunctional characteristics of Nelore females synchronized for FTAI.Materials, Methods & Results: Sixty five lactating female Nelore (Bos taurus indicus) were used. On a random day, denominated day 0 (D0), the 65 Nelore females received a progesterone-releasing device associated to the application of 2.0 mg of estradiol benzoate intramuscularly (IM). On D9, the progesterone-releasing intravaginal devices were removed and was administered 500 μg of cloprostenol sodium IM; 0.6 mg of estradiol cypionate IM and 300 UI of Equine Chorionic Gonadotropin IM. At this point, the animals were marked with a marking stick for the determination of the estrus expression. On D11 of the synchronization protocol, the animals were characterized in two groups: without estrus expression (WO/ ESTRUS) and with estrus expression (W/ ESTRUS). The evaluation of the follicle diameter (FOLD), of the follicle wall area (FOLA), of the follicle wall vascularization (FOLV) and the percentage of vascularization in the area of the preovulatory follicle wall (%FOLV) were conducted on D11 using B-mode ultrasonography and color Doppler and then the artificial inseminations were performed. The evaluation of the corpus luteum diameter (CLD), the total area of the corpus luteum (CLA), of the area of vascularization of the corpus luteum (CLV), of the percentage of vascularization of the in the area of the corpus luteum (% CLV) and the collection of blood for the evaluation of the serum levels of progesterone were carried out on D24. The analysis of the serum progesterone concentration were performed by the chemiluminescence method using the Access immunoassay systems Progesterone, with a sensitivity of 0.1 ng/mL. The diagnosis of gestation was carried out by transrectal ultrasonography on D45.  The animals of the WITH ESTRUS group presented superior FOLD, FOLA, FOV (P < 0.05) averages to those presented by the cows of the WITHOUT ESTRUS group. In relation to the luteal characteristics, in the WITH ESTRUS group the cows exhibited averages for CLD, CLA, CLV and P4 significantly higher than those of the WITHOUT ESTRUS group. However, the bovines of the WITH ESTRUS group presented a % CLV similar to the presented by the females of the WITHOUT ESTRUS group. As for the fertility rates, there was difference between the experimental groups WITH ESTRUS and WITHOUT ESTRUS.Discussion: The present work demonstrated the impact of the estrus expression on the follicular morphological parameters, therefore in accordance with other studies. These authors show a relation between the estrus expression and levels of estradiol, which is directly related to the sperm transport in the female reproductive tract, oocyte maturation and fertilization directly affecting the fertility of females submitted to the FTAI program. Similarly, there was an interrelation between the estrus expression and the luteal morphological parameters, corroborating with the findings of some researches, where were verified higher luteal morphological parameters associated to higher conception rates in cows that demonstrated estrus behavior in the FTAI. Therefore, the estrus detection can be used as a tool to direct matings in synchronization protocols, promoting the identification of the animals with a higher probability of conception, owing to better follicular and luteal hemodynamic conditions.