15 FERTILITY LEVELS IN EWES TREATED WITH MEDROXIPROGESTERONE ACETATE OR FLUOROGESTONE ACETATE SPONGES PLUS EQUINE CHORIONIC GONADOTROPIN IN DIFFERENT PHASES OF THE OESTRUS CYCLE

Abstract

Commercial programs of estrus synchronization in ewes are performed with intravaginal sponges impregnated with synthetic progestagens such as medroxiprogesterone acetate (MAP) or fluorogestone acetate (FGA). Normally, sponges are placed deep into the vagina in cyclic females at different points in the estrus cycle. The aim of the present study was to compare fertility levels in ewes with estrus synchronized by using commercial sponges impregnated with either 60 mg of MAP (eMAP) or 30 mg of FGA (eFGA), placed during the follicular or luteal phase of the estrus cycle, plus eCG. A total of 273 sexually mature Merino ewes belonging to the same herd, aged between 2.5 and 5.5 years and clinically healthy, were scanned by transrectal ultrasonography with an 8-MHz probe (Aquila, Esaote-Pie Medical, Maastricht, The Netherlands) to visualize the ovarian status in the reproductive season. Ovaries without CL and follicles ≥4 mm were considered in the follicular phase, whereas ovaries with CL and follicles ≤4 mm were considered in the luteal phase. Thus, estrus synchronization was performed in 134 ewes treated with eMAP (Sincrogest, Ovejero Lab, Spain), of which 40 were in the follicular phase and 94 were in the luteal phase. In contrast, 139 ewes were treated with eFGA (Sincropart, CEVA Lab, Barcelona, Spain), of which 42 were in the follicular phase and 97 were in the luteal phase. Sponges were removed in all females after 12 days and 500 IU of eCG (Serigan, Ovejero Lab, Leon, Spain) was given. Ewes were then placed jointly with rams, at a ratio of 5 to 1, until no signs of mount were detected. Twenty-five days after the withdrawal of males, pregnancy rates were determined by transrectal ultrasonography with an 8-MHz probe. Fertility levels of synchronized estrus with the eMAP or eFGA sponges during the follicular or luteal phase are expressed as a proportion of ewes and were analyzed by a chi-square Pearson analysis. Significance was set at a level of P < 0.05. After ultrasound scanning of the initial 273 ewes, 30.04% were considered to be in the follicular phase, whereas 69.96% were in the luteal phase of the estrus cycle. Pregnancy rate for eMAP-treated ewes during the follicular phase was 67.50% and was 69.14% for treatments during the luteal phase. In addition, for ewes treated with eFGA, pregnancy rate was 73.80% during the follicular phase and 73.19% during the luteal phase. No significant differences were found in pregnancy rates for either eMAP- or eFGA-treated ewes during the follicular or luteal phase of the estrus cycle. In conclusion, these results suggest that during the breeding season, fertility levels were not affected in ewes whose estrus was synchronized with intravaginal sponges impregnated with MAP or FGA. In addition, pregnancy rates were not affected when the synchronization treatments began during the follicular or luteal phase of the estrus cycle.