Role of the adrenals in the maintenance of pregnancy in cows.

On Day 215 of gestation, cows were treated as controls (Group 1), bilaterally ovariectomized (Group 2), bilaterally adrenalectomized (Group 3) or bilaterally adrenalectomized and ovariectomized (Group 4). The mean +/- s.e.m. lengths of gestation (days) were 278 +/- 3 (N = 5), 270 +/- 2 (N = 7), 277 +/- 1 (N = 5) and 219 +/- 1 (N = 3) in Groups 1, 2, 3 and 4 respectively. In Group 4, serum progesterone concentrations declined to undetectable levels within 24 h after surgery and all the cows aborted 3-6 days later. All the cows in Groups 1, 2 and 3, except 1 cow in Group 2, completed gestation and delivered live calves. Progesterone concentrations in Group 2, cows declined to approximately one-third those of cows in Groups 1 or 3. All 3 cows in Group 4 and 7/8 in Group 2 had a retained placenta. At 1 and 2 days after surgery there were no significant differences in plasma levels of oestradiol-17 beta, but by the third day this difference was significant (P less than 0.01). Oestrogen levels were high before parturition in cows in Groups 1 and 3 but were not noticeably elevated in those in Groups 2 and 4. The abrupt termination of pregnancy and negligible concentrations of progesterone in adrenalectomized-ovariectomized cows indicate that the bovine adrenals contribute to progesterone production and are capable of maintaining pregnancy after ovariectomy at 215 days of gestation.