Effect of photoperiod on gonadotrophin concentrations in domestic turkeys

Abstract

1. Circulating immunoreactive luteinising hormone (LH) and follicle stimulating hormone (FSH) concentrations have been measured during photoperiodically-induced changes in the reproductive state of turkeys. 2. In a period of sexual quiescence on short photoperiods (6L: 18D) LH concentrations were higher during the hours of darkness in both sexes. 3. Transfer to long photoperiods (16L: 8D) stimulated a rapid increase in LH and FSH concentrations. This was maintained for between 2 to 3 months when the concentrations of both gonadotrophins decreased as the birds became photorefractory. 4. Return to short photoperiods had no immediate effect on the concentrations of LH and FSH in females. The concentration of LH was increased during the 3rd week of short photoperiods when the hens were moulting. 5. LH concentrations fluctuated during the ovulatory cycle and were highest about 6 h before ovulation.

Variations in plasma prolactin, thyroid hormones, gonadal steroids and growth hormone in turkeys during the induction of egg laying and moult by different photoperiods

“…Concentrations of these hormones decrease as egg production declines and, except for a transitory increase in LH concentration at the onset of moult, are low in birds after the photoperiod is decreased (Godden and Scanes, 1977). Hormones other than gonadotrophins are also involved in the regulation of reproductive activity in 144 SGANES, SHARP, HARVEY, GODDEN, CHADWIGK AND NEWCOMER birds.…”

“…Egg production in domestic turkeys is controlled by length of photoperiod (Clayton and Robertson, 1960) and when the photoperiod is increased for 33-weekold turkeys there is an increase in the concentrations of luteinising hormone (LH) and follicle stimulating hormone (FSH) in the blood (Godden and Scanes, 1977). Concentrations of these hormones decrease as egg production declines and, except for a transitory increase in LH concentration at the onset of moult, are low in birds after the photoperiod is decreased (Godden and Scanes, 1977).…”

Relationships between broodiness expression laying persistency and concentrations of hormones during the first productive period in turkey hens (Meleagris gallopavo)

“…It does not seem to be related to the expression of broodiness since it is observed in both broody and non-broody hens (Etches and Cheng, 1982) and no differences in basal plasma prolactin concentrations were observed between broody and non-broody hens (Bacon et al, 1983). The photoinduced increase in LH induces a rise in oestrogens (Bajpayee and Brown, 1972;Wineland and Wentworth, 1975) and in progesterone (Mashaly and Wentworth, 1974;Godden and Scanes, 1977). In addition, changes in the circulatory level of these steroids have been reported to be associated with the changes in physiological states: laying, incubating and out-of-lay (Gu6men6 and Williams, 1992).…”

“…Depending on the period of treatment, it may also delay the !photoinduced 1988). In addition, the injection of anti-prolactin serum increased plasma LH concentrations of incubating bantam hens (Lea et al, 1981) while high levels of prolactin blocked the post-castration increase in circulating LH in incubating hens (Zadworny and Etches, 1987 Godden and Scanes, 1977;. In the meantime, a large increase in plasma prolactin levels is associated with the onset of egg-production and the concurrent high plasma LH concentrations in hens of a high egg-producing strain (Etches and Cheng, 1982), but not in hens of a low egg-producing strain .…”

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

“…Testicular steroids, mainly testosterone, act with FSH to regulate spermatogenesis and also exert negative feedback on the secretion of the gonadotrophins [1]. In addition, plasma LH concentrations increase during the phase of rapid growth of the testes in males subjected to photostimulatory daylengths both in the fowl and turkey [2][3][4][5]. In males from previously named species, LH and testosterone are discharged in pulsatile patterns during both the photophase and the scotophase of the nycthemere.…”