124 RELATIONSHIPS BETWEEN PREOVULATORY FOLLICLE AND CORPUS LUTEUM BLOOD FLOW IN MARES

Colour- and power-Doppler ultrasonography have recently been used as potential new technologies to assess the degree of vascular perfusion of the ovary and follicles for research and clinical studies of ovarian and follicle hemodynamics and to predict fertility in horses, cattle and humans. In the present study, the following hypotheses were tested: (1) preovulatory follicle (POF) diameter (≥30 mm), but not blood flow, is repeatable between cycles within the same mare; (2) POF diameter and blood flow are good indicators of follicle status; (3) double POF have similar blood flow; and (4) highly vascularized POF produce corpora lutea (CL) with greater blood flow. Non-lactating mares (n = 13; 5 to 21 years old) of mixed breeds were used from March to May in the Northern Hemisphere. Follicle diameter and vascularity of the follicle wall before the first and second ovulations of the season and vascularity of the first CL were measured daily using transrectal colour-Doppler ultrasonography. The vascularity of the follicle wall and CL was based on the display of the blood-flow signals visualised in a slow, continuous-motion evaluation. Statistical analyses were performed by the SAS MIXED procedure, ANOVA and Student's t-tests and Spearman's correlation. A total of 26 periovulatory periods were evaluated. Unexpectedly, there were 84.6% (11/13) and 61.5% (8/13) double dominant POF and 30.8% (4/13) and 46.2% (6/13) double ovulations in the first and second periovulatory periods, respectively. The POF diameters were highly correlated (r = 0.68; P < 0.0001) between the first and second periovulatory periods. The diameter of the POF 5 days before the first ovulation was larger (P < 0.004) than before the second ovulation of the year. However, the POF vascularity did not differ between those periods. For 4 days before ovulation (Day 0), the diameter and blood flow of the POF were greater (P < 0.05) than for those follicles that underwent atresia in single- and double-ovulatory mares. The POF diameter and blood flow were positively correlated in ovulatory (r = 0.51; P < 0.0001) and in atretic (r = 0.32; P < 0.02) follicles. In double-ovulatory mares, POF diameter and blood flow increased (P < 0.0006) for 5 days before ovulation, with no difference between the 2 follicles in the same cycle for each parameter. The POF blood flow was positively correlated (r = 0.32; P < 0.0009) with CL vascularity during the first periovulatory period (Day –7 to +6) of the season. Furthermore, a positive correlation (r = 0.58; P < 0.01) was observed between the maximum vascularity of the POF and its subsequent CL. In conclusion, although preliminary, our results demonstrated that (a) POF vascularity is not repeatable within individuals; (b) potential atretic POF have low blood flow; (c) double POF have similar vascularity; and (d) greater blood flow to the POF is associated with higher CL vascularity.