Changes in Plasma Concentrations of Luteinizing Hormone, Progesterone, and Estradiol-17β in Peripubertal Turkey Hens under Constant or Diurnal Lighting1

Possible circadian fluctuations and long-term changes in concentrations of reproductive hormones in peripubertal female birds is poorly documented in comparison with mammalian species. Our objective was to document changes in concentrations of several reproductive hormones the several days before and after initial pubertal preovulatory surges of LH in turkey hens photostimulated with either constant (24L:0D) or diurnal (14L:10D) lighting. The hens were cannulated for hourly blood sampling, starting 10 days after photostimulation and continuing until all hens had laid at least two eggs. First eggs were oviposited between 16 and 24 days after photostimulation, and egg production ranged from two to nine eggs/hen during the experimental period. With both lighting treatments, concentrations of LH declined slightly, concentrations of progesterone (P4) increased, and concentrations of estradiol-17β (E2) were constant the 3–4 days prior to initial LH surges with no circadian fluctuations in hormone concentrations. Most (10 of 13) initial preovulatory surges of LH were coupled with ovulations, and all LH surges were coupled with P4 surges. Those LH and P4 surges not coupled with ovulations (blind surges) occurred with both lighting treatments, but the incidence of blind surges was higher with diurnal lighting. The interval between LH and P4 surges was longer between the first and second surges than between subsequent surges, when the interval was approximately 26 h. The duration of LH surges (7.4 ± 3.0 h) was shorter than that of P4 surges (10.0 ± 2.0 h). We conclude that, in the peripubertal female turkey, 1) prior to puberty (first LH-P4 surges), there are no circadian fluctuations in concentrations of LH, P4, and E2, 2) 3 days prior to initial LH surges, E2 concentrations are stable, LH concentrations decline slightly, and P4 concentrations increase, and 3) surges of LH are coupled to surges of P4 but LH-P4 surges are not always coupled to ovipositions (blind surges), possibly because of internal ovulations.