Effect of ovariectomy on the course of gestation in the grey squirrel (Sciurus carolinensis)

In the grey squirrel pregnancy continues in the absence of the ovaries from day 16 of gestation. Since the investigation was performed on squirrels caught in the wild the stage of gestation was estimated from plasma progesterone levels, volume of corpora lutea at ovariectomy and date of parturition for those squirrels which did give birth. Three squirrels ovariectomized in early pregnancy did not give birth. Plasma progesterone levels after ovariectomy were lower than those found in normal pregnancy squirrels suggesting that the corpora lutea are a continuing source of progesterone even at a time when pregnancy can continue in their absence.