Postpartum uterine and ovarian condition affect the foal estrus fertility in Mangalarga Marchador mares?

This study was conducted to evaluate the follicle development, uterine morphology, and fertility of Mangalarga Marchador mares submitted to natural breeding in the first postpartum estrous cycle. Eight mares were evaluated with ultrasound equipment every three days, from the second to the 42nd day after delivery. During this period, follicular diameter, corpus luteum persistence, appearance and diameter of the horns and uterine body in addition to weight and body condition were evaluated. Postpartum reproductive efficiency was verified through conception and estrous repetition rates. Data were submitted to Pearson's correlation analysis, chi-square test, linear and quadratic regression. Ovulation occurred between days 14.5 ± 2.5 postpartum. The mean range of the follicular wave was 11.75 ± 2.5 days, with a daily follicular growth rate of 3.6 ± 0.6 mm. There was reduction of the uterine body of 20.6 ± 1.4 mm, characterizing uterine involution in mares. High conception rate (75%) was found during foal heat and variation in body weight and body condition score after parturition did not present significant interference in the other parameters. Therefore, follicular dynamic, uterine involution, weight, and body condition variation were compatible with the postpartum estrus onset in Mangalarga Marchador mares and did not interfere in conception rates.