EFFECTS OF THE EMBRYO ON UTERINE MORPHOLOGY AND FUNCTION IN MARES

Surgical ligations of the uterine horns on Day 11 (ovulation designate d Day 0) were used to restrict the embryonic vesicle to the uterine bo dy and caudal uterine horns; uterine characteristics were assessed in the isolated cornual segments. Transrectal palpation was used to asses s uterine tone and ultrasonic scanning was used to assess uterine edem a (scores 1-4, minimal to maximal for both end points). Tone was great er (P<0.05) or tended to be greater (P<0.07) for uterine-intact mares (n = 5) than for uterine-ligated mares (n = 5) on each of Days 13-19. A significant interaction indicated higher endometrial echotexture sco res over Days 17-24 in the uterine-intact mares than in the uterine-li gated mares. In another experiment, cornual ligations were done before Day 11 to restrict the embryo to the side of ovulation (n = 10). Sign ificant horn by day interactions indicated that the uterine horn conta ining the embryo (ipsilateral horn) had greater tone and smaller horn diameter than the contralateral horn over Days 13-23; tone and diamete r of the ipsilateral horn were similar to those of pregnant uterine-in tact mares (n = 6). A significant horn by day interaction indicated hi gher endometrial echotexture scores for the ipsilateral horns in mares with ligations and for both horns in mares without ligations than for the contralateral horn over Days 17-25. Uterine contractility, assess ed ultrasonically at the uterine body, was decreased (P<0.05) in uteri ne-ligated mares (no conceptus exposure in the uterine body) on each o f Days 11-14, relative to uterine-intact mares. Results indicated that the early conceptus promotes an increase in uterine tone with a corre sponding decrease in diameter, enhanced endometrial folding, and incre ased uterine contractility through a local mechanism. That is, a great er effect was detected in the uterine segments exposed to the conceptu s or its secretory products than in the segments without conceptus exp osure.