RESUMEN
A field trial was conducted to assess the efficacy of a combined prostaglandin F(2)alpha analogue (cloprostenol) and dexamethasone treatment as an abortifacient in feedlot heifers. Heifers were grouped according to stage of gestation as follows: Group I, one to four months, n = 37: group II, four to six months, n = 40: group III, six to eight months, n = 40: group IV, one to eight months, n = 29. Heifers in groups I, II and III received a simultaneous intramuscular injection of 500 mug cloprostenol and 25 mg dexamethasone at the time of rectal palpation for pregnancy diagnosis. Heifers in group IV were subjected to rectal palpation for pregnancy diagnosis but received no treatments. Heifers were observed daily for two weeks for abortion and rectal palpations were done 50 days after treatment to determine reproductive status. HEIFERS ABORTING AFTER TREATMENT WERE AS FOLLOWS: Group I, 37/37; group II, 37/40, group III, 37/40; group IV, 0/29. In each of groups II and III there was one pregnancy and two cases of fetal mummification. The numbers of abortions in groups I, II and III were significantly different from that in group IV (P