Evidence of a photoinducible phase for the release of luteinizing hormone in the domestic hen

Abstract

Hens raised on a schedule of 8 h light : 16 h darkness (8L : 16D) were exposed to changes in photoperiod at 17 or 18 weeks of age. These involved exposure to either an abrupt increase in photoperiod to 16 h per day or to skeleton photoperiods comprising a main period of 7\m=.\75or 4 h light together with a pulse of 15 min or 4 h light provided at different times during the period of darkness.An increase in photoperiod to 16 h per day stimulated a two-to threefold increase in the plasma concentration of LH within 1\ p=n-\ 3 days. Interruption of a 7\m=.\75L :16D schedule by 15 min light between 13\m=.\75and 19\m=.\75h after the beginning of the main photoperiod stimulated LH secretion in the immature and adult hen and a higher rate of lay than that of the 8L : 16D control group. There was a significant (P < 0\ m=. \ 01) correlation between the concentration of LH in the plasma and the rate of lay. The photostimulated rise in the plasma concentration of LH in the immature hen was not associated with any increase in the responsiveness of the pituitary gland to LH releasing hormone. Of the treatments in which a 15-min pulse of light was provided, the schedules of 7\m=.

Oviposition patterns and plasma melatonin rhythms in response to manipulations of the light: Dark cycle

“…Morris (1978) suggested that the extra effectiveness of relatively short light periods in ahemeral cycles is caused by the fact that, every 'afternoon', new hours are lighted. This interpretation is in accordance with the well-accepted idea of a photo-inducible phase located approximately 11 to 16 h after dawn (Follett and Sharp, 1969;Follett, 1973;Siopes and Wilson, 1980;Wilson, 1982). These researchers have shown that light which falls within these sensitive hours will stimulate reproductive function.…”

Effect of temporary transfers to 14 h on age at first egg in domestic pullets reared on 8-h photoperiods

“…As a consequence, the delaying effect of the decrease more or less cancels out the stimulatory influence of the increase. It is speculated that this is because the increased concentrations of circulating gonadotrophin that would undoubtedly have resulted from the increment in photoperiod (Wilson, 1982;Lewis et al, 1994Lewis et al, , 1999, were subsequently suppressed or curtailed by the decrease in daylength (Urbanski and Follett, 1982;Lewis et al, 1998), and that this slowed, but did not prevent, sexual maturation. Unfortunately, plasma gonadotrophin concentrations were not measured in this experiment, so this proposal cannot be substantiated.…”

“…Although two-to three-fold increases in plasma LH were observed in 17-week-old domestic pullets within 1-3 d of a transfer from 8-to 16-h photoperiods (Wilson, 1982), and significant increases in plasma LH, and ovarian and oviducal weights were recorded in dwarf broiler breeders 14 d after they had been transferred from 8-to 20-h photoperiods , no advance in age at first egg (AFE) occurred when pullets were temporarily transferred from 8 h to 10, 12, 14 or 16 h for 1 or 2 d at various ages between 10 and 16 weeks of age (Lewis and Gous, 2004).…”

Research note: an amendment to the model for predicting age at sexual maturity for growing pullets of layer strains given two opposing changes in photoperiod

“…1). This is in marked contrast to luteinizing hormone (LH), which shows a two- to three-fold rise in plasma concentration within 1–3 days of pullets being transferred to a stimulatory daylength (Wilson 1982). However, circulating LH concentrations are poorly correlated with rate of sexual development in pullets (Lewis et al 1994).…”