Intrauterine movement of the early conceptus in barren and postpartum mares

The equine embryonic vesicle has been shown to be highly mobile prior to day 15, moving from one horn to the other many times per day. In Experiment 1, intrauterine mobility patterns of the vesicle were compared between barren and postpartum mares on days 12, 13, or 14, using an ultrasound instrument. Location of the vesicle (left horn, right horn, body) was determined every five minutes during six two-hour trials in each group. Averaged over all trials, the vesicle moved from one horn to the other 1.1 times per two-hour trial. There were no significant differences between barren and postpartum mares in the mean number of times the vesicle changed its location or in the amount of time the vesicle spent in the left versus right horn. In postpartum mares, the number of location changes and the time spent in a horn were not different between the formerly gravid horn and the nongravid horn. The reported frequent attachment of the vesicle to the formerly nongravid horn was not, therefore, attributable to a difference in the extent of mobility or the amount of time spent in the nongravid horn during the period of high intrauterine mobility. In Experiment 2, the rate of movement of the embryonic vesicle within the uterine body on days 12 through 14 was estimated to average 3.4 mm/min (range, 0-14 mm/min), based on fixed points of reference (cranial end of cervix, uterine cysts). Using time-lapse photography at one-minute intervals, a 14-day embryonic vesicle was monitored as it approached a cyst in the lumen of the uterine body. The vesicle encroached upon the cyst, forming an indentiation in the vesicle. It then moved over the top of the cyst to the other side and continued moving in the same direction.