Estrogen-induced pseudopregnancy in gilts: Its use in estrus synchronization and subsequent influence on litter response

The effectiveness of using estrogen-induced pseudopregnancy followed by PGF(2alpha) (Lutalyse) treatment to synchronize estrus in gilts and the subsequent effect of pseudopregnancy on litter parameters was examined in two experiments. Experiment 1 consisted of a control (n = 49) group and a pseudopregnant (n = 49) group. Pseudopregnant gilts received PGF(2alpha) between Days 25 and 38 and were bred at the ensuing estrus. Ninety-two percent of the gilts responded to PGF(2alpha) and exhibited estrus in 4.9 +/- 0.2 (Least Square Mean +/- SEM) days. Duration of estrus was longer in pseudopregnant compared to control gilts (2.8 vs 1.7 d, P<0.001). Experiment 2 consisted of a control (n = 24) group and a pseudopregnant (n = 24) group. All pseudopregnant gilts received PGF(2alpha) on Day 38 and 79% responded with a mean onset of estrus at 5.2 +/- 0.2 d. As in Experiment 1, duration of estrus was longer in gilts from the pseudopregnant group (2.2 vs 1.7 d, P<0.005). The percentage of farrowing was similar for both groups in both experiments, and no differences existed in the number of pigs born and those alive at 21 d post partum. Litters from gilts in the pseudopregnant groups were heavier at birth than those in the control group (Experiment 1, 17.21 vs 15.25 kg, P<0.01; Experiment 2, 15.31 vs 13.55 kg, P<0.02) and at 21 d (Experiment 1, 60.81 vs 56.79 kg, P<0.01; Experiment 2, 51.89 vs 46.96 kg, P<0.02). Survival rate at 21 d was higher in offspring from pseudopregnant gilts in both experiments (Experiment 1, 85.3% vs 78.2%, Experiment 2, 91.4% vs 81.2%).