This observation suggests that some turkeys have entered puberty by 18 wk of age under either the SD or LD lighting program. Similar developmental changes in LH and T have been observed in male chickens. The increased hormone concentrations at about 18 wk of age are possibly associated with testis growth and semen production since semen production was first observed in some individual birds 1 or 2 wk subsequent to increased plasma LH and T. antibiotics levaquin
The increased level of LH and T at 18 wk of age may be due to decreased sensitivity of GnRH neurons to negative feedback of steroids, but no direct evidence for this mechanism is available in birds. In mammals, similar increases in LH are observed, and a hypothesis has been proposed that at the onset of puberty, decreased negative feedback of steroids (estradiol) on GnRH-secreting neurons results in increases of LH release frequency that might induce sexual maturation. The turkeys exposed to LD from the early age of 10-12 wk produced semen earlier, and with a higher percentage of birds producing semen at an earlier age, than those exposed to the SD photoperiod. This earlier onset of puberty was associated with higher levels of LH after 18 wk of age.