Pre-ovulatory follicle affects corpus luteum diameter, blood flow, and progesterone production in mares

Color Doppler ultrasonography was used to study the temporal relationships between pre-ovulatory follicle (POF) and corpus luteum (CL) diameter and blood flow, with systemic progesterone (P4) concentration during two transitional ovulatory seasons in mares. Variables of POF and CL/P4 were evaluated for 6days before and 17days after ovulation, respectively. Evaluations were performed during two consecutive estrous cycles in spring and fall seasons, and during the last estrous cycle of the season. There were significant correlations among POF and CL variables, and P4 concentration that ranged from 0.24 to 0.95, and among the ratios of different variables that ranged from 0.39 to 0.92. There were linear regressions (P<0.01-0.001) for all comparisons among different variables. The POF diameter before the first ovulation of the season was larger (P<0.05), and POF vascularity was less (P<0.05), than in the last estrous cycle during the season. The CL blood flow was less (P<0.01) during the last compared with first pre-ovulatory period of the season. The POF diameters were positively correlated (r=0.67) during the two pre-ovulatory periods of spring and fall. Results provide evidence that the POF affects CL diameter and blood flow, and subsequently P4 production, and that POF diameter is repeatable within the same individual during different seasons.