Serum concentrations of prolactin, luteinizing hormone, growth hormone, corticosterone, progesterone, testosterone and oestradiol in relation to broodiness in domestic turkeys (Meleagris gallopavo).

Variations in concentrations of LH, GH, prolactin, corticosterone, oestradiol, testosterone and progesterone in serum were followed over a 24 h period (14 h light:10 h darkness) in laying and broody turkeys and in turkeys suspected of becoming broody (pre-broody hens). In laying hens marked variations in LH and gonadal steroid levels were observed in relation to the ovulatory cycle of the bird. These patterns of hormone secretion were not seen in either group of broody birds. Levels of GH in serum were very variable and showed no correlation with the egg-laying or light:darkness cycle and the concentrations did not differ between the respective physiological states. A nocturnal increase in the concentration of corticosterone in serum was observed in all three groups of turkeys and the concentration was occasionally higher in the pre-broody and broody birds than in the laying hens. The serum prolactin concentration in each group was also very variable and showed no obvious relationship with the ovulatory or photoperiodic cycle. The mean circulating prolactin concentration throughout the 24 h period did not differ significantly between the groups. These results suggest that broodiness in the domestic turkey is not initiated or maintained by enhanced prolactin secretion.