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 spo nges impregnated with different doses of MAP in an ewe herd and to determin e the effects of such treatments upon estrus incidence, interval to estrus onset and pregnancy rate. Polyurethane sponges impregnated with 40, 50 and 60 mg of MAP were prepared. Real amounts of progestagen on sponges were che cked prior to sponge treatment insertion. During autumn 1999, 608 cyclic Me rino ewes were treated with intravaginal sponges impregnated with different doses of MAP (groups I, 40; II, 50 and III, 60 mg). After 14 days, sponges were removed and residual levels of MAP (RMAP) on removed sponges were mea sured by spectrophotometry. Real amounts for unused sponges were 39.60+/-1. 10, 44.10+/-1.06 and 59.10+/-1.26 mg for the intended doses of 40, 50 and 6 0 mg MAP respectively. RMAPs were different (p<0.05) among groups (I: 17.98 +/-1.97 mg; II: 24.32+/-2.03 mg; III: 34.25+/-3.23 mg). Absorbed levels of MAP were. not different among groups (I: 21.62+/-1.97 mg; II: 19.78+/-2.03 mg; III: 24.85+/-3.23 mg). Artificial insemination was performed in 16 ewes from Group I, 17 ewes from Group II and 11 ewes from Group III, 12 h after estrus onset. There were no differences among groups, neither for estrus i ncidence (I: 79.27%; II: 77.42%; III: 80.87%) nor interval to estrus onset (I: 55.94+/-1.87h; II: 56.74+/-1.13 h; III: 57.70+/-1.02 h). There were als o no differences among groups for pregnancy rate (I: 43.75%; II: 52.94%; II I: 45.45%). It was concluded that under similar conditions, a dose as low a s 40 mg MAP could be effectively used for estrus synchronization in cyclic Merino ewes. (C) 2000 Elsevier Science B.V. All rights reserved.