Plasma progesterone level during delayed implantation, gestation and postpartum period in the armadillo

Blood samples were obtained weekly from 21 pregnant armadillos during the months of June through May and analyzed by radioimmunoassay for progesterone concentration. Following ovulation and mating, the plasma concentration of progesterone remained elevated (greater than 13 ng/ml) during the 3.5 months of delayed implantation. As implantation occurred in October, the plasma concentration of progesterone increased and remained at approximately 20 ng/ml in all animals through March. Ten of the animals delivered during March and April in captivity. The date of the blood sample collection was calculated as the number of days before or after parturition. Progesterone concentration was not decreased prior to delivery and remained elevated for as long as 55 days following parturition.