Progesterone mediates nutritionally induced effects on embryonic survival in gilts

The role of plasma progesterone as a potential mediator of nutritionally induced effects on embryonic survival in gilts was assessed in two experiments. Gilts were individually fed 2.5 kg/d for one estrous cycle and inseminated 12 and 24 h after onset of next estrus (d 0). In Exp. 1, 52 gilts were randomly allocated to either N (1.5 x maintenance feed/d) or H (twice maintenance/d) groups from d 1. In 21 gilts, blood samples were collected on d -1, 0, 1, and 2, and gilts were slaughtered on d 3 to 5. Interval from LH peak to postovulatory progesterone rise was shorter (P = .02) in N (28.8 +/- 2.3 h) than in H (38.6 +/- 3.2 h) gilts, with no difference in rate of rise. Embryonic survival was 86.5 +/- 2.1 and 74.2 +/- 6.2% in N and H gilts, respectively, with a higher variability in Group H (P < .05). In 31 gilts, blood samples were collected 48 and 72 h after estrus onset, and gilts were slaughtered on d 11 and 12. Plasma progesterone concentrations at 72 h were higher (P = .02) in N than in H gilts (14.7 +/- 1.2 vs 10.8 +/- 1.0 ng/mL). Uterine plasmin/trypsin inhibitor concentrations were higher (P = .03) in H than in N gilts, but IGF-I concentrations did not differ. In Exp. 2, gilts were randomly allocated to either H or HP groups on d 1. The HP gilts were given six injections of progesterone (75 mg every 12 h) starting 24 h after estrus onset. Gilts were slaughtered on d 28 +/- 3. Plasma progesterone concentrations at 36, 48, 60, 84, and 108 h after estrus onset were higher (P < .001) in HP than in H gilts. Embryonic survival was also higher (P = .004) in HP (84.8 +/- 2.6%) than in H gilts (70.0 +/- 4.0%). Thus, periovulatory plasma progesterone can be the mediator of nutritionally induced effects on embryonic survival.