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 progester one, as an index of ovarian activity, during the estrous cycle of nons easonal Shiba goats is affected by seasonal changes, and 2) to learn i f the pulsatile secretion of ovarian progesterone can be estimated fro m samples obtained by cannulation into the caudal vena cava via the fe moral vein. Progesterone concentrations in jugular venous plasma durin g the estrous cycle in spring (May) were similar to those in autumn (N ovember). Plasma progesterone concentrations in the jugular vein and c audal vena cava monitored for 10 h on Day 12 of the estrous cycle in s pring 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 plasm a progesterone in the caudal vena cava during both seasons were 3.1- t o 4.7-fold and 1.7- to 2.4-fold those in the jugular vein, respectivel y. The degree of change in the peak magnitude and the base-line concen tration of progesterone were higher in the caudal vena cava than in th e jugular vein. These results indicate that progesterone secretion dur ing the estrous cycle in nonseasonal goats is not affected by seasonal changes, and suggest that the pulsatile secretion of ovarian progeste rone can be evaluated better from samples obtained from the caudal ven a cava, near where progesterone is released, than from those obtained from the jugular vein.