Vascular perfusion and the volume of the preovulatory follicle are affected by the temperament of Nellore cows

Abstract

The aim of this study was to evaluate the effect of temperament on vascular perfusion and morphological characteristic (volume) of the preovulatory follicle (POF) and corpus luteum (CL) of Nellore cows submitted to timed artificial insemination (TAI). The effect of temperament on cortisol, P4 concentrations and on ovulation rates was also evaluated. To achieve this, the ovarian cycles of 201 beef cows were synchronized, and temperament assessments were carried out using the chute score and chute exit score at the time of TAI. According to the individual scores, the animals were classified into adequate temperament (ADQ) or excitable (EXC). Blood samples were collected at the time of TAI and 7 days later to measure cortisol and P4, respectively. Color Doppler ultrasound assessments were performed to determine the volume, and blood flow of the POF and CL at the time of TAI (D0) and seven days later (D7), respectively. The ovarian cycle synchronization and ovulation rates were compared between the ADQ and EXC groups using the chi-square test while hormonal concentrations and ultrasound variables were compared using a general linear model. Multiple comparisons between groups were conducted using Tukey's contrasts. The data were expressed as means and standard error. The number of color pixels (p ≤ 0.01), intensity of color pixels (p ≤ 0.01) and volume (p ≤ 0.01) in the POF were all lower for the EXC group. However, cortisol concentrations were higher in the EXC group compared to the ADQ (p ≤ 0.01). This was related to stress during TAI management. The number and intensity of the color pixels in the CL showed no difference between groups, however, the volume was lower (p ≤ 0.01) for the EXC group. There was no difference between groups regarding ovarian cycle synchronization, ovulation rates and P4 concentration. However, the P4/CL volume ratio was higher in the EXC group. The results indicate that the excitable temperament in Nellore cows has important endocrine effects and reflects on the ovarian structures, with less follicular blood flow and a reduction in the volume of the POF and CL, however, without compromising the ovulation rate.