Selected Factors that Affect the Measurement of Plasma Progesterone Concentrations in Pregnant Ewes

Abstract

A competitive protein-binding technique was used to measure progesterone concentrations in the peripheral plasma of pregnant ewes. Neither haemolysis of blood nor thawing of plasma samples affected plasma progesterone concentration. Blood samples should be chilled immediately upon collection but subsequent to centrifugation immediate chilling of the plasma samples is not critical. No consistent diurnal variation in progesterone concentrations was evident but there was large apparently random day-to-day variation in progesterone concentrations for any ewe. Although a significant positive correlation was found between endogenous progesterone and corticosteroid concentrations, the present study failed to correlate experimentally elevated plasma corticosteroid concentrations with progesterone concentrations. Progesterone concentrations varied greatly between ewes at the same stage of pregnancy.