Plasma progesterone levels during delayed implantation in the European badger (Meles meles).

There was a biphasic pattern of progesterone secretion during the year. Delayed implantation was characterized by low concentrations from February to June, a significant (P less than 0.001) increase during July, August and September, and a return to low levels in October-November. A second significant increase (P less than 0.001) was observed in December and early January just before the presumed time of implantation.