Efeito da intensidade do estro avaliada automaticamente sobre a taxa de concepção de vacas leiteiras inseminadas com sêmen sexado

Abstract

The intensification of dairy farming has driven the use of reproductive biotechnologies to enhance reproductive efficiency and genetic progress. In this context, Fixed-Time Artificial Insemination (FTAI) combined with sex-sorted semen enables a higher production of female offspring, although it may result in lower conception rates. Evidence indicates that cows exhibiting estrus with greater intensity have higher preovulatory estradiol concentrations, suggesting a possible link between estrus expression and fertility. This study aimed to evaluate the effect of estrus intensity— observed at the end of an FTAI protocol or during spontaneous estrus—on the conception rate of Holstein × Gir crossbred dairy cows inseminated with sex-sorted semen. The experiment was conducted at the Dairy Cattle Unit of the Glória Experimental Farm (Federal University of Uberlândia) using lactating cows subjected to a progesterone- and estradiol-based hormonal protocol and inseminated with sexsorted semen. Estrus intensity was measured using an automated activity monitoring system (COWMED®), and animals were classified according to intensity: weak (n=13), moderate (n=42), and strong (n=36). Conception rates were determined via ultrasound diagnosis 32 days after FTAI. Statistical analyses were performed using logistic regression in the MINITAB software, with statistical significance set at P ≤ 0.05. A trend toward a positive association between estrus intensity and conception rate was observed; cows exhibiting strong estrus achieved a 52.8% pregnancy rate, whereas those with weak and moderate estrus achieved 30.8% and 35.7%, respectively. Days in milk at the time of insemination had a significant effect (P=0.016) on conception rate, revealing a lower rate in cows with up to 90 days in milk (25.6%) compared to those between 91 and 120 days (54.2%) and those beyond 121 days (53.6%). Milk production near the time of insemination or at peak lactation did not influence the occurrence of strong estrus. It is concluded that estrus intensity has a positive effect on conception rate; cows with fewer than 90 days in milk exhibit lower conception rates, and the incidence of strong estrus is higher in cows with more than 120 days in milk.