Prostaglandin F concentration in serum of hens and cocks.

Prostaglandin F (PGF) concentrations in the serum of laying and nonlaying hens and of cocks at various times during a day were measured by radioimmunoassay. The serum concentration of PGF was higher in laying hens than in nonlaying hens or cocks without regard to time of day. In all birds, the concentration showed a peak at 2 h after onset of light (0700 h). In laying hens on the day of laying the fourth egg of a sequence, two peaks were found: one at 2 h after onset of light and another at the time immediately after oviposition. The results suggest that the serum concentration of PGF in both male and female chickens shows a daily change and that in laying hens it also shows a change associating with oviposition.