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Progesterone and Estrogen Concentrations in Gilts with Delayed Parturition^1,2,

University of Kentucky, Lexington 40546

Abstract

Twelve pregnant gilts were assigned to three treatments (four gilts per treatment): (1) corn oil (control) injected subcultaneously four times daily from day 110 of gestation until onset of lactation; (2) 25 mg progesterone (P₄) injected subcutaneously four times daily from day 110 of gestation through day 113, or (3) 25 mg P₄ injected subcutaneously from day 110 through day 115 of gestation. Excluding one gilt on treatment 2 which farrowed on day 110, average lengths of gestation for control gilts and gilts receiving treatments 2 and 3 were 113.3 ± 1.2 (SE), 115.6 ± .7 and 118.0 ± .4 days. Associated mean percentages of live births were 87.4 ± 5.9, 48.8 ± 24.4 and 2.5 ± 2.5, respectively. P₄ averaged 2.9 ± .6 ng/ml in blood serum of control gilts during the 24 hr preceding parturition. P₄ was released in a sporadic pattern by gilts on treatment 3, resulting in higher P₄ concentrations (9.0 ± 1.7 ng/ml) for the same prepartum period. Concentrations of P₄ in serum of gilts on treatment 2 averaged 7.6 ± 1.6 ng/ml, intermediate to, but not different from, concentrations of P₄ in controls and gilts on treatment 3. Concentrations of estrogen in serum of control gilts averaged 6.2 ± 1.3 ng/ml during the 24 hr preceding parturition, whereas concentrations of estrogen in gilts treated with P₄ were reduced (P<.01) to below 2 ng/ml during the same prepartum period. The erratic pattern of concentration of P₄ during and after administration of exogenous P₄ may reflect a disturbance of the secretion or metabolism of endogenous P₄. We suggest that failure to suppress P₄ post-treatment plus reduced estrogenic stimulation impedes the birth process and contributes to the high incidence of stillbirths observed in gilts with progestin-delayed parturition.

¹ The investigation reported in this paper (No. 80-5-6) was conducted in connection with a project of the Kentucky Agr. Exp. Sta. and is published with the approval of the director.

² This work supported in part by a grant from the National Pork Producers Council.