Metabolites of Progesterone and Estrogen in Domestic Sow Urine. II. Changes Pre- and Postpartum and Effect of Feeding 6-Methyl-17-Acetoxy-Progesterone

Administration of progesterone as late as day 28 of gestation delays parturition in the rabbit (Heckel and Allen, 1938). Endogenous progesterone dominates the uterus until day 30 (Schofield, 1957), and labor cannot be induced with oxytocin prior to day 30 (Csapo, 1956). The dominance of estrogen just prior to parturition in the rabbit was suggested by Csapo (1956), and the activity of uterine smooth muscle in vitro supported this suggestion (Schofield, 1957). Rapid increases in estrogen excretion in urine during late pregnancy in the cow (Hunter et al., 1970) and sow (Edgerton and Erb, 1971) indicate that an increase in estrogen metabolism may be more important in domestic species than a decrease in progesterone metabolism. The purpose of this study was to define changes in urinary excretion of metabolites of estrogen and progesterone (pregnanes) during the last 2 weeks of pregnancy and the first 7 days postpartum. In one group gestation was prolonged for another study (Curtis, Rogler and Martin, 1969) by feeding Repromix beginning at 100 days of pregnancy.