Plasma estradiol-17.BETA. and progesterone levels and ovarian activity in postpartum cows.

Plasma estradiol-17β (E₂) and progesterone (P) levels were studied about jugular blood samples collected either every day in follicular phase or every other day in luteal phase from 3 postpartum cows (2 Holsteins and a Japanese black) and a Holstein cow in which cesarean section was performed on the 4-5th month of pregnancy. At the same time, ovarian activities were examined daily by rectal palpation and estrous signs were checked twice daily during follicular phase. <BR>Until postpartum first ovulation, which occurred at 14-40 days postpartum, plasma P levels did not exceed 0.4ng/ml. E₂ levels during this period were rather low, but showed a little increase before first ovulation. The first ovulation was not preceded by estrous signs. <BR>The length of first estrous cycle in the 3 postpartum cows was shorter (9-14 days) than that observed in the ordinary cycle length. Corpora lutea in this stage seemed to be subfunctional and plasma P levels never exceeded 1.0ng/m_l. <BR>On the contrary, the cow No. 4 in which cesarean section was performed showed high plasma E₂ and P levels till first ovulation after the operation. These high levels may be originated from re-tained placenta and corpus luteum of pregnancy. The first ovulation was preceded by marked estrous signs in this cow. The corpus luteum in the first estrous cycle (17 days) was also very functional and the patterns of plasma E₂ and P levels were quite similar to those of cycles after second ovulation with normal ovarian activities in the cow No. 2 and No. 3. It was suggested that the ovarian func-tion of this animal had already recovered at this stage. <BR>After second ovulation, nearly normal ovarian activities were confirmed by palpation in 2 (No. 2 and No. 3) of the 3 postpartum cows. In the 2 cows, although some of the subsequent ovulations were preceded by estrous signs, the remaining cows were silent. In these animals, plasma E₂ levels in-creased after ovulation, showed a little peak in luteal phase, then decreased, increased again in follicular phase and showed a peak (4.3-16.7pg/ml) 1-3 days before ovulation. P levels increased after ovulation, showed a peak (2.5-8.0ng/ml) in luteal phase, decreased suddenly at 5-8 days before next ovulation and the low levels were maintained at the time of ovulation. <BR>In the cycle of cow No. 1, cystic corpus luteum (CCL) developed and ruptured during palpation 9 days after ovulation. The follicle in the ipsilateral ovary developed rapidly after the CCL rupture and became cystic, and the cystic follicle existed about 60 days thereafter. During the CCL forma-tion, plasma P levels were below 0.8ng/ml, but after the rupture, they elevated along with luteiniza-tion of CCL and showed a peak of 6.1ng/ml. E₂ levels increased rapidly during the cystic follicle formation and elevated to a peak level (12.9pg/ml) 3 days after the CCL rupture and suddenly de-creased thereafter. In the second and third cycles of this animal having a cystic follicle, plasma E₂levels were low. <BR>Plasma E₂ and P levels in 6 estrous cycles with normal estrus were compared to those in 6 cycles with silent estrus. Plasma P levels in the luteal phase in the cycles with silent estrus tended to form the peak earlier and declined more solwly than in the cycles with normal estrus.