Uterine Contraction during the Ovulatory Cycle of the Hen

Abstract
Patterns of uterine contraction (UC) were determined by recording electrical activity of the uterus in the free moving hen. Between 2 ovipositions within a clutch, the frequency of electrical activity remained minimum, but showed a significant increase beginning 5–6 h after the time of ovulation and high levels lasted for 20 h. The frequency started to increase rapidly 5 min before oviposition, reached maximum at the time of oviposition and decreased to the minimum level within 30 min after the oviposition. In contrast to normal layers, hens laying shell-less eggs or internal layers showed persistently low electrical activity after premature oviposition or after internal ovulation, respectively. But despite the absence of an egg in the oviduct, both types of birds displayed the same UC peak at the expected time of oviposition as that in the normal bird. The frequency of electrical activity of the uterus remained low for several hours after oviposition of the terminal egg (Ct) of a clutch, but was elevated for about 5 h and showed a peak about 1 h before ovulation of the first egg (C1) of the next clutch separated by single day. The results suggest that the UC peak at oviposition may be attributable to either or both actions of the posterior pituitary hormones and the postovulatory follicles and that the process of ovulation may be involved in the UC peak.