Impact of a progesterone-releasing intravaginal device and inflammatory reaction on ovarian activity in embryo-recipient anestrus mares

This study aimed to correlate the inflammatory reaction (IR) caused by a progesterone-releasing intravaginal device (P4) with ovarian activity and pregnancy rate (PR) in embryo-recipient anestrus mares (to decrease the spring transitional period). 50 animals were assigned to three groups: GP4 (P4 group; n = 16), GP4OH (P4 + oxytetracycline hydrochloride and hydrocortisone sprayed onto the device; n = 14), and GNP4 (no intravaginal P4; n = 20). The administration protocol for GP4 was: Day 0, 750 mg P4 + ovarian examination by ultrasonography (US) + vaginal sample collection; Day 8, US; Day 11, P4 removal + 7.5 mg PGF2α + US + second vaginal sample collection; Days 13 to 16, US; Days 17 to 21, US + 750 IU hCG to mares with follicles 35 mm or more in diameter; Days 19 to 23 US (ovulation check); Days 24 to 28, embryo transfer + intravenous flunixin meglumine; and Days 30, US pregnancy diagnosis. The GP4OH and GNP4 mares received the same administration protocol as GP4, except that no P4 device was administered to the GNP4 group on Day 0. Although neutrophil-mediated IR occurred in the GP4 and GP4OH groups, the IR was significantly reduced in GP4OH as compared with that in GP4 (P < 0.0001). From Day 0 to Day 17, the GP4 and GP4OH mares developed a greater number of follicles per animal than did the GNP4 mares (P < 0.05), and the average diameter of the follicles was larger in the GP4 and GP4OH mares. The ovulation rates in GP4, GP4OH, and GNP4 mares were, respectively, 43.7%, 64.3%, and 30.0%, and ovulation occurred at 6.8, 6.5, and 23 days after P4 removal (P < 0.05). On Day 17, endometrial edema was verified in 50%, 64.2%, and 35.0% of the GP4, GP4OH, and GNP4 mares, and the PRs after embryo transfer were 80%, 100%, and 66.6%, respectively. Although intravaginal devices caused IR in both the device-recipient groups (P = 0.0001), IR and vaginitis had no negative impact on follicle diameter, ovulation rate, period to ovulation after the removal of P4, endometrial edema, or PR. In addition, P4 reactivated the ovarian function and the IR eliminated a large percentage of bacteria (Bacillus spp., Enterobacter spp., Proteus spp., Pseudomonas spp., and Staphylococcus spp.), especially in GP4; the application of oxytetracycline hydrochloride and hydrocortisone on the devices reduced the severity of vaginitis.