Effect of Photoperiod on the Concentrations of Corticosterone and Luteinizing Hormone in the Plasma of the Domestic Hen

Abstract

Ovipositions in hens maintained under schedules of 16h light : 8h darkness (16L : 8D) or 8L: 16D were restricted to a 12h period of the day while in hens maintained on continuous light, ovipositions occurred at times throughout the whole of the 24h day. In hens maintained in continuous light a significant rise in the plasma concentration of corticosterone was observed 11-9h before ovulation/oviposition. In hens in 16L : 8D there was an increase in the concentration of corticosterone in the plasma during the first 1.5h of darkness which, under that schedule, coincides with the onset of the "open period" for the occurrence of the preovulatory release of LH. In hens ovulating the first egg of a sequence the rise in the secretion of corticosterone was only transient and levels fell as preovulatory concentrations of LH rose to a peak. However, in hens undergoing an ovulation late in a sequence or in those not expected to ovulate, the concentration of corticosterone in the plasma continued to rise to attain a maximal concentration 8h later. In hens maintained in 8L : 16D there was a tendency for the concentration of corticosterone in the plasma to increase at the beginning of the open period, 4 h after the onset of darkness, though this rise was much smaller than that observed at the beginning of the open period of hens on 16L : 8D. A further, more pronounced, increase in concentration of corticosterone was observed between 11 and 15h after the onset of darkness. It is suggested that the rise in the concentration of corticosterone at 11-9 h before ovulation in hens in continuous light reflects the beginning of an open period with a free-running circadian periodicity of 26-27 h.

Comparisons of time intervals and plasma LH concentrations during the ovulatory cycle of broiler breeder hens maintained under either a 24 H light:dark cycle or continuous light

“…Because these hens were fed a restricted diet at regular times in continuous light, they were experiencing approximately 24-h cycles of feeding and fasting and thus were entrained to an approximate 24-hourly Zeitgeber (Table 4). Indeed, the pre-ovulatory LH peaks observed in the hens housed in continuous light occurred in a restricted part of the day, similar to that observed when the same hens (Table 3) or laying strain hens (Wilson and Cunningham, 1981;Gow et al, 1985) were maintained in 24-h light:dark cycles.…”

“…It is unlikely to be due to an increase in the periodicity of the circadian rhythm controlling the open period because the hens may have remained entrained to a 24-h Zeitgeber, even when held on continuous light. A similar increase in oviposition interval seen in Australorp and White Leghorn hens (Gow et al, 1986) and Ross Tints (Wilson and Cunningham, 1981) transferred from a 24-h light:dark cycle to continuous light could be explained in this way because the open period became unentrained. There was no indication of a decrease in egg production in the broiler breeder hens, as was observed in laying strain hens transferred to continuous light (Gow et al, 1986).…”

“…1). This observation is in contrast to the expected relatively uniform distribution of ovipositions in laying strain hens in continuous light (Morris, 1977;Wilson and Cunningham, 1981;Gow et al, 1986). It appears that the circadian rhythms in the broiler breeder hens were not free-running under conditions of continuous light and noise and may have been entrained by phase-setting signals such as feeding or temperature (McNally, 1947;Morris, 1961;Wilson et al, 1964;Payne et al, 1965).…”

Developmental changes in the diurnal rhythm of secretion of corticosterone and LH in the domestic hen

“…In contrast, in adult hens maintained on the same photoschedule, plasma concentrations of corticosterone only start to increase at about the onset of darkness (Wilson & Cunningham, 1981). Also in 4-and 8-week-old hens maintained on 16L:8D and 4-week-old hens main¬ tained on 8L:16D plasma concentrations of corti¬ costerone attained their maximal value earlier in relation to the onset of light than has been observed in adult hens maintained on the same photoschedules (Wilson & Cunningham, 1981). The diurnal rhythm in the secretion of corticosterone in immature hens main¬ tained on 8L : 16D and 16L : 8D was most pronounced at 4-5 and 8-5 weeks of age.…”

“…In birds the rhythm of secretion of corticosterone is influenced by daylength (Boissin & Assenmacher, 1970;Wilson & Cunningham, 1981). However, even under a constant photoperiod of 16h light: 8h dark¬ ness ( 16L : 8D), changes in the phase-angle of the corti¬ costerone rhythm in relation to the cycle of light and darkness occur in association with sexual development of the domestic duck (Wilson et al 1982) and male white-throated sparrow (Fivizzani & Meier, cited in Meier, 1976).…”