Effects of estrogen and prostaglandin on progesterone-delayed farrowing

Effects of estradiol benzoate and prostaglandin F_2α (PGF_2α) on concentrations of progesterone and estrogen in serum and the percentage of live births were determined in 21 gilts treated with exogenous progesterone in late gestation. All gilts received progesterone (25mg s.c. four times daily) from Days 108 through 113 of gestation. Gilts receiving no other treatments (controls) had elevated levels of progesterone through 1800 h on Day 114 (29.2 ± 11.4 ng/ml) and farrowed at 115.6 ± 0.3 d of gestation with a relatively low percentage of live births (66.8 ± 17.3). Gilts treated with PGF_2α administered at 0600 h on Day 114 had less (P<0.01) progesterone by 1800 h (7.0 ± 1.3 ng/ml) relative to that of the controls, but they had similar gestation lengths (115.5 ± 0.3) and percentages of live births (50.0 ± 16.2). Administration of estradiol benzoate (10 mg) to gilts at 0600 h on Day 114 did not reduce progesterone on Day 114 or the gestation length relative to that of the control gilts, but it did increase (P<0.05) the percentage of live births (100%).