Evaluation of changes in blood flow of the uterine artery by Doppler ultrasonography during the estrous cycle in lactating Bos indicus cows

•Blood flow dynamics through Doppler ultrasound in the estrous cycle of Sahiwal cow.•RI of uterine arteries, as a measure of blood flow, is considerably lower at estrus and ovulation than during diestrus.•PI is substantially elevated during diestrus compared to estrus and ovulation in Sahiwal cows.

The objective of this study was to evaluate the changes in uterine blood flow (UBF) based on the resistance index (RI) and the pulsatility index (PI) by Doppler ultrasonography throughout the estrous cycle in lactating Sahiwal cows (n = 9). Cows were randomly selected during their spontaneous estrus. UBF was examined on alternate days in all cows during the estrous cycle. The results revealed that the mean RI values were higher (P < 0.05) on day −1 (estrus) than on day 0 (ovulation). The mean RI values followed a consistent pattern on days 2, 4, 6, and 8 (metestrus to early diestrus) and were lower (P < 0.05) than on days 10, 14 16, and 18 (diestrus to early proestrus). The RI and corpus luteum (CL) size negatively correlated during its static phase (r = −0.99; P < 0.05). The mean RI was greater (P < 0.05) in high producers than in low producing cows. The mean PI value was higher (P < 0.05) on day 10 than on day −1 and day 0. Similarly, the mean PI values were lower (P < 0.05) on days 2 and 4 than on day 10. The PI value remained significantly lower (P < 0.05) on day 2 than on day 8 of the estrous cycle. There was a positive correlation between RI and P4 (r = 0.70; P < 0.05) and PI and P4 (r = 0.56; P < 0.05) during the estrous cycle. It is concluded that the RI of uterine arteries, as a measure of blood flow, is considerably lower, while the PI is substantially elevated during diestrus compared to estrus and ovulation in Sahiwal cows.