IDENTIFICATION OF THE CORPUS-LUTEUM IN NONPREGNANT MARES AT DAYS 13 TO 16 USING ULTRASOUND

Two hundred mares of mixed breeding were examined with ultrasound for pregnancy on 273 occasions, between Days 13 and 16 after ovulation, an d found to be empty. At this stage the visible presence of any corpora lutea were noted including the side and level of echogenicity. The ut erus was examined for endometrial edema and free luminal fluid. The ce rvix was palpated per vagina for tone, relaxation and edema. Interovul atory intervals were recorded. The corpus luteum (CL) was clearly visi ble on the side ipsilateral to the recorded ovulation in 73% of 134 ca ses examined on Day 13, 65% on Day 14, 43% on Day 15 and 42% on Day 16 . No CL was visible in 17 cases (Day 13), 19 (Day 14), 15 (Day 15) and 9 (Day 16) and of these 14, 12, 6 and 4 cases were thought to have su ffered premature luteolysis due to luteal phase bacterial endometritis . The mean interovulatory interval for this group was 15.9, 17.9, 15.7 and 16.0 days, respectively, compared with 21.9, 21.6, 21.9 and 21.3 days for normal mares where the CL was still visible.