Effect of intraovarian proximity between dominant follicle and corpus luteum on dimensions and blood flow of each structure in heifers

An intraovarian positive physiologic coupling between the extant CL and the ipsilateral preovulatory follicle (PF) or the future or established postovulatory dominant follicle (DF) was studied in 26 heifers. Ovaries were scanned by ultrasonic imaging from Day 16 (Day 0 = ovulation) of the preovulatory period until Day 6 of the postovulatory period. Hemodynamics of the follicles and CL were assessed by color-Doppler ultrasonography. When the PF and CL were ipsilateral compared with contralateral, blood-flow resistance in wall of the PF was lower (P < 0.04) on Days –2 and –1, and percentage blood-flow signals in the CL approached being greater (P < 0.08) on Days –4 to –1. During the postovulatory period, percentage of DF wall with blood-flow signals (44.1 ± 1.2% vs. 31.4 ± 2.8%) and percentage of CL with blood-flow signals (51.8 ± 1.2% vs. 42.5 ± 3.1%) were each greater (P < 0.05) when the two ipsilateral structures were adjacent (distance between antrum and CL wall, ≤ 3 mm) than when separated. On Day 0, the distance between follicle and ipsilateral CL was less (P < 0.02) for the future DF than for the future largest subordinate. Growth rate between Days 0 and 2 averaged over all growing follicles was greater (P < 0.01) when the follicles were ≤3 mm from the CL (1.1 ± 0.1 mm/day) than when farther from the CL (0.9 ± 0.1 mm/day). Results supported the hypotheses that (1) a positive intraovarian coupling occurs between the PF or postovulatory DF and the extant CL and (2) the coupling is enhanced when the ipsilateral DF and CL are in close proximity.