PROGESTERONE THERAPY DURING EARLY-PREGNANCY AND EMBRYONAL SURVIVAL INPRIMIPAROUS WEANED SOWS

The experiment was conducted in primiparous sows to determine whether progesterone supplementation during early pregnancy could improve embr yonal survival and to confirm a functional relationship between proges terone concentrations in the postovulatory period and embryonal surviv al. Thirty-four primiparous sows were fed for ad libitum intake from f arrowing to d 21 of lactation, restricted to 50% of ad libitum intakes between d 22 and 28, weaned on d 27, and then fed for ad libitum inta ke from weaning until d 28 of gestation. The number of pigs per litter was standardized to nine within 48 h after farrowing. After mating, s ows were allocated either to be treated with ethyl oleate (control gro up) or to receive progesterone (P-4) therapy (progesterone group) as 2 mg of p(4)/kg(.75) i.m., every 12 h from 36 to 96 h after onset of st anding estrus. There was no difference in the weaning-to-estrus interv al(123.5 +/- 5.7 vs 123.1 +/- 5.9 h) and number of corpora lutea (18.1 +/- .4 vs 18.3 +/- .5) between the control and progesterone sows (P > .05). Compared with a more gradual increase in control sows, plasma pr ogesterone concentrations in progesterone sows increased immediately f rom.6 +/-.1 ng/mL at 36 h after onset of standing estrus to 6.3 +/-.5 ng/mL(P <.001) 12 h later and remained high. Total number of embryos, total embryonal survival rate, number of viable embryos, and viable em bryonal survival rate on d 28 of gestation in control sows were greate r than in progesterone sows (13.3 +/- 1.0 vs 8.5 +/- 1.1; 73.1 +/- 4.7 vs 47.3 +/- 5.4%, P <.005; 12.6 +/-.9 vs 7.1 +/-.9, and 69.5 +/- 4.2 vs 39.7 +/- 4.8%, P <.0005; respectively). Embryonal survival in contr ol sows was comparable to that in previous experiments using the same primiparous sow model, and the relationship between plasma progesteron e and embryonal survival seemed similar. However, using the treatment schedule adopted, progesterone not only failed to reverse the presumed detrimental effect; of increased catabolism in the late lactation per iod on embryonal survival, but also adversely affected the number of e mbryos at d 28 in 7 out of 15 progesterone-treated sows.