Effect of Ovariectomy on Concentration of Progesterone in Blood Plasma and Urinary Estrogen Excretion Rate in the Pregnant Bovine

Blood from the jugular vein and urine were collected from cows before and after ovariectomy during pregnancy, to evaluate the effect of ovariectomy on the concentration of progesterone in plasma, the urinary estrogen excretion rate, and their relationship to pregnancy maintenance. Plasma progesterone concentration in 115 samples of blood from intact cows averaged 36 ].1 ng/ml and did not change significantly from 181 days of pregnancy through 12 hours post-partum. However, the peak level was 44 2.7 ng/ml at 261 days, compared with 33 3.6 ng/ml at parturition. Plasma progesterone at seven days postovariectomy was unchanged compared with the presurgical concentration, but declined significantly thereafter and remained low through one day post-partum. The average for 109 samples taken nine or more days after surgery was 17 0.9 ng/ml. Levels as low as 10 ng/ml in some cows were associated with maintenance of pregnancy, though all cows which maintained pregnancy 264 days or longer following ovariectomy from 200 to 237 days had abnormal parturition and retained fetal membranes. Plasma progesterone levels were as low following removal of the CL-bearing ovary as after bilateral ovariectomy. Urinary estrogen excretion rate was generally maintained after ovariectomy, with some evi-R.