Mobility of the early equine conceptus

Movement of the conceptus within the uterine lumen of barren mares was studied by daily ultrasound examinations on days 11-20 and by rectal palpation on days 15-48 (Experiment 1) and by ultrasound examinations 3 or 4 times per day at 2-4 hour intervals on days 11-16 (Experiment 2). In addition, broodfarm records were analyzed to compare side of ovulation with side of embryo attachment (Experiment 3). The vesicle was found in opposite uterine horns for 43% of the successive, daily, ultrasound examinations on days 11 and 12, 12 and 13, 13 and 14, and 14 and 15; 24% of the successive examinations on days 15 and 16; and 8% on days 16 and 17. No movement was detected after day 17. The vesicle was found in opposite horns during 41% of the successive examinations at 2-4 hour intervals on days 11, 12, 13, 14, and 15, but no movement was detected on day 16. In addition, no transuterine migration was found by rectal palpation between the day of first detection of an embryonal enlargement (mean, day 17) and day 48. During ultrasound examination on days 11-15, the vesicle was found significantly more frequently in the left horn (66% of the observations) than in the right horn (34%); however, final attachment occurred more frequently in the right horn (63% of the mares). In analyses of brood-farm records, ovulation occurred with equal frequency in left and right ovaries in barren and lactating mares, but with significantly greater frequency in the left ovary (63%) in maiden mares. Regardless of the side of ovulation, final attachment of the conceptus occurred significantly more frequently in the right horn (66%) in barren and maiden mares, but not in lactating mares.