Two administrations of an intravaginal progesterone device on the induction of ovarian cyclicity in anestrous mares

Abstract

The study aimed to evaluate the effect of double administration of a progesterone (P4) intravaginal device on induction of ovarian cyclicity in mares. Twelve crossbred mares were assigned to one of two groups. The first group (GP4; n=6; 100% in anestrus phase) underwent the following protocol: day (d) 0, 1.9 g of P4 + ultrasound of the uterus and ovaries (US); d7, US; d10, first P4 removal + US; d10-d24, US daily; d28, second P4; d35, US; d40, second P4 removal + US; d40-d54, US daily; and d54-d76, US every other day. The second group (GNP4; n=5; 100% in transition phase) underwent the same protocol as GP4, but without the administration of the P4 device. From d55-d76, 100.0% of the mares in both groups held uterine tonus and 83.3% had endometrial edema; after the first and second P4 removal, 66.7% and 83.3% of GP4 mares, respectively, reached the transition phase. By d76, 50.0% and 80.0% of the GP4 and GNP4 animals, respectively, had ovulated; the average size of the largest follicle increased from d0-d76 in both groups, but was significant only in GP4. Four to five days after the first and second P4 removals in GP4, follicles showed an average growth of 9.0mm. At the end of the study, both groups had follicular medium diameters greater than 34mm (P>0.05). Ovulations correlated with body condition scores (P<0.05). In conclusion, two administration of P4 affected ovarian cyclicity in anestrous mares, and synchronized follicular waves and ovulation.