Correlations of corpus luteum blood flow with fertility and progesterone in embryo recipient mares.

The aim of this study was to evaluate the correlation between the corpus luteum vascularization with the concentration of progesterone and the fertility of embryo recipient mares. Mangalarga Marchador mares (n = 33) were distributed into groups according to the days (D) after ovulation, as follows: D3 (n = 8), D4 (n = 8), D5 (n = 9), and D6 (n = 8). The evaluations of the corpus luteum, endometrium, and blood collection to quantify the progesterone concentration were carried out on D3, D4, D5, and D6. Among the parameters evaluated, only progesterone concentration on D6 differed from the other groups (P 0.05) by the day of embryo transfer, whose percentages were 37.50% (3/8) on D3, 50% (4/8) on D4, 66.70% (6/9) on D5, and 62.50% (5/8) on D6. It was estimated that with each increase on the day of embryo transfer, the pregnancy rate increases. The results allow to conclude that the corpus luteum vascularization in mares, evaluated by Doppler ultrasound, correlates with progesterone concentration and the embryo transfer day.