Abstract
A single intramuscular injection of pregnant mare serum gonadotropin (PMSG) was made daily for eight successive days into incubating and brooding Gifuijdori hens. Ten out of eleven incubating hens injected stopped incubating, but none of five brooding hens injected stopped brooding. The ovarian and oviduct weight was increased by the PMSG injection in both incubating and brooding hens, but the degree of the increase was less in the brooding hens. Plasma concentrations of estradiol-17β and progesterone were also increased by the PMSG injection. The increase in the estradiol-17β concentration of the brooding hens delayed from that of the incubating hens, and the increrase in the progesterone concentration was later in the brooding hens than in the incubating hens. The results suggest that the ovary of incubating or brooding hens is capable to respond to gonadotropin and its responsiveness is lower in brooding hens than in incubating hens probably because of the presence of chicks to be brooded.
