Endocrine patterns of the mare at term.
The levels of progesterone and total progestins increased during late pregnancy and then fell dramatically during the last few days before parturition, although birth occurred in the presence of significant amounts of plasma progesterone. Oestrogen levels decreased slowly but insignificantly until birth occurred, and then remained at a low level until the post-partum oestrus 10 to 12 days later. Total 11beta-hydroxycorticosteroids were unchanged from Day 45 before to Day 15 after birth. The endocrine pattern of one ovariectomized pregnant mare during the last month of gestation was similar to that of the intact mares. A normal cyclic progesterone and total progestin pattern was observed at the post-partum ovulation. Oestrogen levels did not change significantly but corticosteroid levels increased significantly between Days 15 and 22 post partum. Progestin, oestrogen and corticosteroid levels during the first 24 hr after birth were consistently higher in the foal than in the maternal plasma.