Accumulation of Fluid in the Infundibulum During the Estrous Cycle in Mares

The funnel-shaped cranial portion (infundibulum) of the oviduct is contiguous with the ovulation fossa in mares. An accumulation of fluid in the infundibular area was discovered by transrectal ultrasonic imaging and was studied daily in both oviducts of 12 mares from day –10 to day 10 (day 0 = ovulation), and from day –6 to day 6 during 35 estrous cycles of young, intermediate, and old mares (n = 8 mares/group). The infundibulum was identified by processes (fimbriae) and folds in the pocket of fluid. The amount of fluid accumulation was scored from 0 to 3 (nil to maximum). Frequency of detection of fluid in the infundibular area increased between day –10 (46% of oviducts) and day –3 (88%), and decreased between day –3 and day 7 (8%; P < .002). The day-to-day profile for changes in the score for amount of fluid was significant (P < .0001) and similar to the profile for frequency of detection of the infundibulum. The profiles for the two infundibular end points and scores for endometrial echotexture (an indicator of edema) were similar to the reported profile for systemic estradiol concentrations. The frequency of infundibulum detection was greater (P < .0009) for the side ipsilateral to the preovulatory follicle and ovulation (51%) than for the opposite side (36%). No difference among ages was found for either oviductal end point. Results indicated that changes in the amount of fluid accumulation in the infundibular area and endometrial edema were estrous cycle dependent and similar to previously reported changes in systemic concentrations of estradiol.