Estrus expression and pregnancy rates in heifers primiparous and multiparous Nelore cows subjected to timed artificial insemination with strategic use of gonadotropin-releasing hormone

Abstract

We evaluated the effects of nulliparous, primiparous, and multiparous conditions on the estrus and pregnancy rates in females that did not show estrus but were treated with gonadotropin-releasing hormone (GnRH) at the time of timed artificial insemination (TAI). Nelore females (n = 531) were allocated according to the following categories: nulliparous (n = 144), primiparous (n = 132), and multiparous (n = 255). The animals received a conventional TAI protocol, and estrus expression was identified by the absence of paint in the sacrococcygeal region on the day of TAI. Females that did not show estrus were treated with 10 μg of GnRH together with insemination. The rates of estrus and pregnancy were analyzed using a logistic regression model (P < 0.05). The estrus expression was lower (P = 0.006) in the primiparous (61.36%) group than in the nulliparous (76.39%) and multiparous (75.69%) groups. Similar pregnancy rates were observed in females that showed estrus (nulliparous 84.54%, primiparous 86.42%, and multiparous 80.31%; P = 0.39) and in females that did not show estrus and received GnRH (nulliparous 41.18%, primiparous 56.86%, and multiparous 58.06%; P = 0.24). The total pregnancy rates were also similar (P = 0.98) among the categories (nulliparous 74.3%, primiparous 75.0%, and multiparous 74.9%). The primiparous females had a lower rate of estrus, and the pregnancy rates were similar among the categories that received GnRH.

Effect of estrus behavior on the paint removal score of the sacral region of nulliparous Bos indicus

“…These results were expected, as heifers subjected to the protocols, FTAIs manifested estrus with ovulation before the group's average (Carvalho et al, 2016). In this study, 62.5% of the animals completed the observation period (48 h after P4 removal) under a PRS of 3, a percentage consistent with reports by Nogueira et al (2019), Rodrigues et al (2019), andBonato et al (2021). This result supports previous findings that lactating Bos indicus cows in the postpartum period exhibit a PRS 3 of 53-70% in response to TAI protocols.…”

“…Behavioral estrus expression in beef cattle at FTAI programs serves as a strategy to identify females with a higher likelihood of pregnancy (Sá Filho et al, 2011;Bonato et al, 2021). Among the various techniques for assessing estrus expression, the paint removal score (PRS) is widely utilized (Nogueira et al, 2019).…”

A utilização de GnRH ou Galectina-1 no momento da IA aumenta a taxa de concepção em vacas de corte submetidas a IATF?

“…Considerando a diferença relativa, na proporção de vacas prenhes, Rodrigues et al (2019) encontraram resultados semelhantes (9,77% com o uso de GnRH) aos reportados na presente pesquisa. Entretanto, analisando as comparações de médias entre os tratamentos, outros estudos, como Bonato et al, (2021) e também não observaram diferenças significativas entre os tratamentos.…”

“…Com isso, várias estratégias estão sendo desenvolvidas para manipular as taxas de concepção em vacas de corte e leite. Utilização de progesterona exógena após a inseminação artificial (IA) (Moreira et al, 2020;Pugliesi et al, 2016), bem como a utilização de dose adicional de prostaglandina F2alfa (Ferreira et al, 2020;Rodrigues et al, 2018), além de componentes vitamínicos, minerais e outros hormônios (Bonato et al, 2021;Lima et al, 2017;Peixoto et al, 2021;Souza et al, 2014).…”

Strategic re-use of intravaginal progesterone devices increases conception rate in primiparous Nellore cows

“…Nellore primiparous cows raised under tropical conditions have been widely studied and found not responding adequately to FTAI protocols. According to Bonato et al (2021), primiparous cows are the most metabolically challenged Nellore matrices, especially when raised in a pasture system receiving only mineral supplementation.…”