Maternal recognition of pregnancy in swine. II. Plasma concentrations of progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha during the estrous cycle and during short and long pseudopregnancy in gilts.

Abstract

Two experiments were conducted to determine plasma progesterone (P4) and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) concentrations in unmated gilts induced to have either short pseudopregnancy (SPP) or long pseudopregnancy (LPP). In experiment 1, estradiol-17 beta (E2) was injected on different combinations of days between Days 11 and 16 of the estrous cycle. For gilts induced to exhibit SPP, the interestrous interval averaged 27.0 +/- 0.4 days compared to the control interval of 20.0 +/- 0.4 days. In experiment 2, E2 injections were given on Days 12 and 13 or on Days 12 through 25. Interestrous intervals in SPP and nonpseudopregnant gilts were 25.6 +/- 0.2 and 19.9 +/- 0.6 days, respectively. Four of six gilts treated with E2 on Days 12-25 were induced to have LPP lasting more than 100 days. In both experiments, plasma P4 declined to baseline approximately 3 days before posttreatment estrus, regardless of type of pseudopregnancy induced. Plasma PGFM peaked 4-6 days before posttreatment estrus in gilts displaying each type of response. In gilts exhibiting LPP, plasma PGFM concentrations tended to increase steadily during pseudopregnancy. These data suggest that the mechanisms of luteolysis during the estrous cycle of unmated gilts and during estrogen-induced SPP and LPP may be similar. The present results suggest that luteal persistence during SPP and LPP may be due to delayed peak release of prostaglandin F2 alpha by the uterus.