Secretion of progesterone during long and short days of the estrous cycle in goats that are continuous breeders

This study was conducted 1) to determine if the secretion of progesterone, as an index of ovarian activity, during the estrous cycle of nonseasonal Shiba goats is affected by seasonal changes, and 2) to learn if the pulsatile secretion of ovarian progesterone can be estimated from samples obtained by cannulation into the caudal vena cava via the femoral vein. Progesterone concentrations in jugular venous plasma during the estrous cycle in spring (May) were similar to those in autumn (November). Plasma progesterone concentrations in the jugular vein and caudal vena cava monitored for 10 h on Day 12 of the estrous cycle in spring were similar to those in autumn. The mean concentration (21.9 to 28.9 ng/ml) and the pulse frequency (6.2 to 7.4 pulses/10 h) of plasma progesterone in the caudal vena cava during both seasons were 3.1- to 4.7-fold and 1.7- to 2.4-fold those in the jugular vein, respectively. The degree of change in the peak magnitude and the base-line concentration of progesterone were higher in the caudal vena cava than in the jugular vein. These results indicate that progesterone secretion during the estrous cycle in nonseasonal goats is not affected by seasonal changes, and suggest that the pulsatile secretion of ovarian progesterone can be evaluated better from samples obtained from the caudal vena cava, near where progesterone is released, than from those obtained from the jugular vein.