Peri-follicular blood flow in the follicle from which ovulation occurs in cows

The hypothesis of the study was that the vascularity of ovulatory follicles (OF) determines the ovulatory status. The peri-follicular blood flow characteristics of OF were sequentially recorded using Color Doppler Imaging ultrasonography from the onset of induced estrus (Day 0) to ovulation at 12 h intervals. The OFs were categorized into two groups based on the timing of ovulation (i) Normal ovulation (OFN) - When ovulation occurred within 36 h after the onset of estrus (n = 18) and (ii) Delayed ovulation (OFD) - When ovulation occurred after 36 h (n = 15). The blood flow velocity, Doppler pulse duration (DPD) and Pulsatility index (PI) of the OF were recorded during each examination. The OF was well vascularized with a detectable blood flow signals, while the subordinate or atretic follicles were devoid of detectable blood flow. On Day 0, the DPD (874.33 ± 56.99 ms) and PI (0.62 ± 0.01) values were less in the OFN when compared to OFD (1140.56 ± 27.54 ms and 1.28 ± 0.15 respectively) group. In the OFD group, ovulation occurred between 36 and 60 h after onset of estrus when the DPD value reduced to 878.17 ms. Based on ROC analysis, it was evident that the DPD value of < 929 ms is a necessary factor for induction of ovulation. The decreased DPD and PI values of the OF on the day of estrus are positive indicators of a normal ovulation process.