Estrus synchronization in ewes treated with sponges impregnated with different doses of medroxyprogesterone acetate

The objectives of this study were to determine residual and absorbed levels of medroxyprogesterone acetate (MAP) after treatment with intravaginal sponges impregnated with different doses of MAP in an ewe herd and to determine the effects of such treatments upon estrus incidence, interval to estrus onset and pregnancy rate. Polyurethane sponges impregnated with 40, 50 and 60mg of MAP were prepared. Real amounts of progestagen on sponges were checked prior to sponge treatment insertion. During autumn 1999, 608 cyclic Merino ewes were treated with intravaginal sponges impregnated with different doses of MAP (groups I, 40; II, 50 and III, 60mg). After 14 days, sponges were removed and residual levels of MAP (RMAP) on removed sponges were measured by spectrophotometry. Real amounts for unused sponges were 39.60+/-1.10, 44.10+/-1.06 and 59.10+/-1.26mg for the intended doses of 40, 50 and 60mg MAP respectively. RMAPs were different (p<0.05) among groups (I: 17.98+/-1.97mg; II: 24.32+/-2.03mg; III: 34.25+/-3.23mg). Absorbed levels of MAP were not different among groups (I: 21.62+/-1.97mg; II: 19.78+/-2.03mg; III: 24.85+/-3.23mg). Artificial insemination was performed in 16 ewes from Group I, 17 ewes from Group II and 11 ewes from Group III, 12h after estrus onset. There were no differences among groups, neither for estrus incidence (I: 79.27%; II: 77.42%; III: 80.87%) nor interval to estrus onset (I: 55.94+/-1.87h; II: 56.74+/-1.13h; III: 57.70+/-1.02h). There were also no differences among groups for pregnancy rate (I: 43.75%; II: 52.94%; III: 45.45%). It was concluded that under similar conditions, a dose as low as 40mg MAP could be effectively used for estrus synchronization in cyclic Merino ewes.