Effectiveness of a novel prostaglandin analog in postpartum mares and mares with early season anestrus

Contents Fifty thoroughbred mares, located at Central-Southern Brazil near Sao Paulo (13 anestrous maiden, 18 anestrous barren mares and 19 postpartum mares) were treated with one to three injections, 48 hrs apart, of 2 mg of the novel PGF analog K 11941*, during the early part of the breeding season. Early season anestrus in these problem mares was compounded by the adverse effects of a drought. Plasma progesterone determinations revealed unexpectedly elevated plasma progesterone levels in 61.5% of the maiden mares, in 77.8% of the barren mares and in 68.4% of the postpartum mares (20 to 25 days postpartum). Treatments with K 11941 initiated luteolysis, heat and ovulations in 91.4, 45.5 an 63.3% of these mares, respectively, but initiated also heat and ovulation in 13% and 33% of mares with baseline progesterone levels. Treatments initiated covert and overt cyclic functions in 17 and 12 of those animals which did not conceive immediately. Fifteen animals with recurrent anestrus received further treatment with K 11941. Ten mares cycling silently were force bred when palpations indicated ovulatory follicles, and 7 conceived. Of the 50 mares treated, 38 became pregnant (76%: maiden mares: 76.9%; barren mares: 77.8% and postpartum mares: 73.7%) with breeding indices of 1.9, 1.36 und 1.57, respectively; and 37 mares gave birth to a live foal (74%), At the same stud, 138 control mares had a foaling rate of 82.6%.