ULTRASONOGRAPHIC CHARACTERISTICS OF THE FOLLICULAR AND UTERINE DYNAMICS IN BELGIAN MARES

Changes in the follicular development and visualization of endometrial folds during the estrous cycle were characterized by ultrasonography in Belgian mares. The secondary follicular wave was observed in only 2 of 7 mares and began in early diestrus (day 1; day 0 = day of ovulati on). The dominant follicle of the ovulatory primary wave was retrospec tively detected on 8.1 +/- 3 days after the day of ovulation (day 0 = day of ovulation). The largest subordinate of the primary follicular w ave was first detected at day 7.6 +/- 1.6. The endometrial folds were most prominent 6.6 +/- 1.3 days before ovulation. Regression of the en dometrial folds was observed to occur 5.5 +/- 1.5 days before ovulatio n. In conclusion Belgian mares appear to have follicular dynamics simi lar to those reported for Thoroughbred horses. The cyclic uterine chan ges observed with ultrasound were more sudden, could only be observed for a short period of time and were observed earlier in relation to ov ulation when compared with observations made in other breeds.