It was hypothesized that a high dose of estrogen in conjunction with a long-acting PGF2 alpha analog would synchronize parturition within a narrow time frame and reduce the incidence of retained placenta. On d 276 of gestation, 14 animals (9 cows and 5 heifers) per group received a placebo (group A), 1 mg of fenprostalene (group B), 50 mg of estradiol-17 beta benzoate (group C), or both (group D). Treatment with estradiol-17 beta benzoate increased serum concentrations of estradiol-17 beta from 228 pg/ml at treatment to 642 and 683 pg/ml at 24 h posttreatment for groups C and D, respectively. Concentration of estradiol-17 beta in group A increased gradually to 526 pg/ml at 24 h prepartum. Progesterone concentrations were reduced by fenprostalene but not by estradiol-17 beta benzoate. Estradiol-17 beta benzoate did not reduce incidence of retained placenta in animals treated with fenprostalene (group B vs. group D) but tended to reduce incidence in uninduced animals (group A vs. group C). Thus, short-term elevation of estradiol-17 beta to normal prepartum concentrations did not regress the corpus luteum, induce parturition, or reduce incidence of retained placenta. However, elevation of estradiol-17 beta for longer periods might enhance placental separation. Conversely, fenprostalene induced calving approximately 2 d after treatment. In this study, 90% of animals treated with fenprostalene calved within a 20-h period, but with a high incidence of retained placenta.
