Estrus Synchronization with Pseudopregnant Gilts Induced by a Single Treatment of Estradiol Dipropionate

The aims of this study were to determine whether a single treatment of estradiol dipropionate (EDP) could induce pseudopregnancy in gilts and to determine the effectiveness of PGF2α treatment on estrus synchronization in EDP-induced pseudopregnant gilts. In experiment 1, gilts were treated with 20 mg of EDP (n=11) or vehicle (n=5) on Day 12 (Day 0=onset of estrus). Establishment of pseudopregnancy was defined as a lack of estrus and maintenance of the plasma progesterone concentration above 1 ng/ml between Days 12 and 36. Nine of 11 gilts (82%) treated with EDP became pseudopregnant. The plasma estradiol-17β level was significantly higher in the EDP-treated gilts than in the control gilts until Day 29. In experiment 2, PGF2α was administered twice with a 24-h interval from Day 36 in pseudopregnant gilts (n=6) or Day 10 in cyclic gilts (control; n=5). Estrus after PGF2α treatment was observed in 83% of the pseudopregnant gilts. The interval from the day of the first PGF2α treatment to the onset of estrus and the peak of the LH surge was significantly shorter in the pseudopregnant gilts than in the control gilts. In experiment 3, six pseudopregnant gilts were bred by artificial insemination at the estrus after PGF2α treatment. The farrowing rate and average litter size did not differ between the PGF2α-treated pseudopregnant and cyclic gilts. These results indicate that a single treatment of EDP on Day 12 of the estrous cycle can induce pseudopregnancy in pigs and that a convenient protocol for administering PGF2α to EDP-induced pseudopregnant pigs is available for estrus synchronization programs in cyclic pigs.