Plasma Concentrations of Prolactin during the Reproductive Cycle of the Domestic Turkey (Meleagris gallopavo)

Plasma concentrations of prolactin were measured by a heterologous double antibody radioimmunoassay during the reproductive cycle of Large White turkey hens. In all hens, there was a large increase in the plasma concentration of prolactin as laying commenced. Six weeks after illumination, the concentration of prolactin reached a maximum of 300 to 400 ng/ml and thereafter the plasma values declined. By 15 weeks after illumination, plasma prolactin had declined to baseline values of less than 10 ng/ml. There was no apparent relationship between the concentration of prolactin and egg production, and there were no differences between the changes in prolactin in plasma from broody and non-broody hens. Broodiness invariably was observed after the large increase in plasma prolactin, but the large increase in plasma prolactin was not invariably associated with broodiness. It was suggested that selective breeding for egg production has favored the retention of a genotype which is insensitive to the antigonadal effects of prolactin.