Ontogeny of luteinizing hormone and estradiol secretion in turkey hens exposed to different photoperiods from hatch to sixty weeks of age

Changes in concentrations of plasma luteinizing hormone (LH) and estradiol- 17 beta in turkey hens were measured during development utilizing stimulato ry and nonstimulatory lighting treatments. All hens were maintained under 2 4 h light (L) from hatch to 3 wk of age, then 16L:8 dark (D) to 10 wk of ag e. From 10 wk of age, three lighting treatments were used: 1) 16L:8D from 1 0 to 60 wk of age (Treatment LD); 2) 6L:18D from 10 to 60 wk of age (Treatm ent SD); and 3) 16L:8D from 10 to 20 wk of age, 6L:18D from 20 to 30 wk of age, and then 16L:8D from 30 to 60 wk of age (Treatment SD-LD). Measurement s of plasma LH and estradiol-17 beta concentrations were based on weekly bl ood samples. Similar patterns of LH were observed in all treatments before 24 wk of age. The concentrations of LH were :high at hatch then declined to low levels a t 10 wk of age and rebounded to high levels at 18 wk of age before declinin g to low levels at about 24 wk of age. Low concentrations of LH were then m aintained for hens on all treatments but were slightly higher in hens on Tr eatment SD from 35 to 60 wk of age. A transitory increase in LH, lasting ab out 3 wk, occurred for hens on Treatment SD-LD after photostimulation. The concentrations of estradiol-17 beta were low and stable for hens on all tre atments when they were not laying but were elevated about 2 wk prior to and during egg laying. All hens on Treatments LD and SD-LD laid eggs; no hens on Treatment SD laid eggs to 60 wk of age. It was concluded that 1) changes in plasma LH and estradiol-17 beta were age related before about 24 wk of age, 2) turkey hens may not be photorefractory at hatch and can lay without juvenile exposure to SD photoperiods, and 3) LD photoperiods after about 2 0 wk of age are necessary for initiation of egg production in turkey hens b efore 60 wk of age.