Effects of Photoperiod and Age on Secretory Patterns of Luteinizing Hormone and Testosterone and Semen Production in Male Domestic Turkeys1

Abstract

The objective of this study was to determine effects of photoperiod and age on the circulating concentrations of LH, testosterone (T), thyroxine (T4), and semen production in male turkeys. Male turkeys from 10 or 12 wk of age were maintained under either a long-day (LD) photoperiod of 16L:8D up to 35 wk (LL), or a short-day (SD) photoperiod of 6L:18D to 29 wk and then an LD photoperiod of 16L:8D up to 35 wk of age (SL). 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 LL group prior to 29 wk of age. Both LH and T levels increased significantly within days in the SL group after the group was switched to LD at 29 wk of age. Higher levels of T4 were present in the LL group prior to sexual maturation. No differences were observed in T4 concentration between lighting treatments after sexual maturation. The LL group first produced semen at 20-22 wk of age, which was about 1 wk earlier than first semen production in the SL group. A significantly larger volume of semen was produced in the LL group at most ages. No further increase in semen production was observed in the first 6 wk after the SL group was switched to the LD photoperiod at 29 wk of age. Pulsatile patterns of LH and T were characterized by serial blood sampling at 13, 23, and 35 wk of age under both the LL and SL photoperiods. The baseline levels of both LH and T in male turkeys were influenced by age and photoperiod. However, pulse characteristics (numbers, duration, and amplitude) of LH did not change with age or lighting treatment, while pulse 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 the age of sexual maturation and induced earlier increased concentrations of LH and T.

Effect of various photoperiods on testicular weight, weekly sperm output and plasma levels of LH and testosterone over the reproductive season in male turkeys

“…Previous studies using commercial breeder turkeys revealed a high degree of sensitivity to photoperiod for TW [10,11], semen output [18], and circulating LH and testosterone concentrations [6][7][8][9]. The present results confirmed previous observations [10,11] that prepubertal male turkeys maintained under constant long days are precocious semen producers (26-29 wk) In .…”

“…We suggest that this cannot be attributed to juvenile photorefractoriness that is expressed in wild birds not having reached full body development [19]. Our study also confirmed previous observations that a short, reputedly non-stimulatory photoperiod may induce precocious sexual maturity (26-29 wk) in a minority (here about 30%) of the experimental population [9]. Hypothetically, such turkeys possess the genetic capacity to reach a functionally reproductive state when subjected to a ''normally'' non-stimulatory environment.…”

“…Indeed, an apparent paradox exists between the persistently low levels of circulating LH and T and the degree of development of the testes and the high rates of semen output observed in Group 2. Yang et al [9] indicated that plasma LH (but not testosterone) concentrations followed a pattern similar to semen production, at least within the first 6-8 wk following sexual maturity. This was observed in Groups 1, 3, and 4.…”

“…Turkey males in semen production exposed to continuous or intermittent light regimes had minor differences in patterns of LH and testosterone secretion [7,8]. Immature male turkeys exposed first to a short (6L:18D) and then to a long photoperiod (16L:8D) had marked increases in plasma concentrations of both LH and testosterone during the first 4 wk following photostimulation [9]; this was followed by an increase in testis weight but not in semen output. A nonreversible regression of the testes followed the onset of sexual maturity in turkey males exposed to long photoperiods from the first weeks after hatching [10].…”

Sex hormones response to feeding intensity in Japanese quail (Coturnix coturnix japonica)

“…The testosterone value of male turkeys ranged from 0.4 to 2.0ng/cm-3 until sexual maturity and reached 4.0ng/cm-3 at 29 weeks of age when semen production increased (Yang et al, (1998). Similarly, Blaszczyk et al, (2006) reported a value range of 4.39ng/cm-3 of plasma testosterone in male quail but at 56 days old with ranges of 1.39-4.39ng/cm-3 (40-66 days of age) for male and 0.23-1.27ng/cm-3 for female over the same period with peak concentration of 1.27ng/cm-3 on the 60 th day.…”