ESTROGEN-INDUCED DELAY OF FARROWING IN SWINE

Eighty-four sows and gilts were assigned to 4 treatment groups to assess the effects of estrogen upon normal and prostaglandin-induced farrowing. Sows in Group 1 were injected with saline and corn oil vehicles at 800 hours on Day 112 of gestation and served as controls. Sows in Group 2 received saline and 3 mg of estradiol benzoate. Sows in Group 3 received 10 mg of prostaglandin F2-alpha (PGF2-alpha) and corn oil, and sows in Group 4 received both the PGF2-alpha and estradiol benzoate. The control sows farrowed at 74.5 +/- 6.8 hours after vehicle injections. Surprisingly, the average time from treatment to onset of parturition was significantly increased (P < 0.05) by the injection of estrogen alone (Group 2 = 100 +/- 9 hours). Closer examination showed that the interval was dichotomous with 6 ot the 21 sows in Group 2 farrowing in less than 54 hours and 14 of 21 sows farrowing only after 100 hours. Prostaglandin injections shortened (P < 0.05) the interval to 41 +/- 8 hours. Litter size averaged 10.9 pigs and was similar for all treatments. As used in this study, there was no advantage to combining estrogen with prostaglandin-induced farrowing. Induced farrowing did not significantly reduce incidence of livebirths, but birthweights were lower (P < 0.05) in prostaglandin-treated gilts (Groups 3 and 4). Weaning weights remained lower for pigs from prostaglandin-treated sows, but treatment-related differences were not significant (P > 0.1). Performance characteristics of estrogen-treated sows and their litters were equal to those of the control sows.