EFFECTS OF PHOTOPERIOD AND AGE ON SECRETORY PATTERNS OF LUTEINIZING-HORMONE AND TESTOSTERONE AND SEMEN PRODUCTION IN MALE DOMESTIC TURKEYS

The objective of this study was to determine effects of photoperiod an d age on the circulating concentrations of LH, testosterone (T), thyro xine (T4), and semen production in male turkeys. Male turkeys from 10 or 12 wk of age were maintained under either a long-day (LD) photoperi od of 16L:8D up to 35 wk (LL), or a short-day (SD) photoperiod of 6L:1 8D to 29 wk and then an LD photoperiod of 16L:8D up to 35 wk of age (S L). Plasma concentrations of both LH and T increased by 17 or 18 wk of age under both photoperiods, but higher levels were attained in the L L group prior to 29 wk of age. Both LH and T levels increased signific antly within days in the SL group after the group was switched to LD a t 29 wk of age. Higher levels of T4 were present in the LL group prior to sexual maturation. No differences were observed in T4 concentratio n between lighting treatments after sexual maturation. The LL group fi rst produced semen at 20-22 wk of age, which was about 1 wk earlier th an first semen production in the SL group. A significantly larger volu me of semen was produced in the LL group at most ages. No further incr ease in semen production was observed in the first 6 wk after the SL g roup was switched to the LD photoperiod at 29 wk of age. Pulsatile pat terns of LH and T were characterized by serial blood sampling at 13, 2 3, and 35 wk of age under both the LL and SL photoperiods. The baselin e levels of both LH and T in male turkeys were influenced by age and p hotoperiod. However, pulse characteristics (numbers, duration, and amp litude) of LH did not change with age or lighting treatment, while pul se characteristics of T did change with age. We conclude that exposing male turkeys to an LD photoperiod from 10 or 12 wk of age advanced th e age of sexual maturation and induced earlier increased concentration s of LH and T.