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

Abstract

Changes in concentrations of plasma luteinizing hormone (LH) and estradiol-17beta in turkey hens were measured during development utilizing stimulatory and nonstimulatory lighting treatments. All hens were maintained under 24 h light (L) from hatch to 3 wk of age, then 16L:8 dark (D) to 10 wk of age. From 10 wk of age, three lighting treatments were used: 1) 16L:8D from 10 to 60 wk of age (Treatment LD); 2) 6L:18D from 10 to 60 wk of age (Treatment 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). Measurements of plasma LH and estradiol-17beta concentrations were based on weekly blood 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 at 10 wk of age and rebounded to high levels at 18 wk of age before declining to low levels at about 24 wk of age. Low concentrations of LH were then maintained for hens on all treatments but were slightly higher in hens on Treatment SD from 35 to 60 wk of age. A transitory increase in LH, lasting about 3 wk, occurred for hens on Treatment SD-LD after photostimulation. The concentrations of estradiol-17beta were low and stable for hens on all treatments 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-17beta 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 20 wk of age are necessary for initiation of egg production in turkey hens before 60 wk of age.