Effect of increasing day length and intermittent lighting schedules in the domestic hen on plasma concentrations of luteinizing hormone (LH) and the LH response to exogenous progesterone

Pullets were raised under a constant photoperiod of 8L:16D until 17 weeks of age at which time they were subjected either to intermittent pulses of light superimposed on a photoperiod of 8L:16D or to a photoperiod of 16L:8D. Exposure of hens, maintained under a lighting schedule of 8L:16D, to hourly pulses of light for either 10 sec, 1 min, or 10 min during the first 8 hr of darkness or to an increased photoperiod of 16L:8D stimulated a rise in the plasma concentration of LH within 3 days and slightly advanced the onset of lay. About 6 weeks after the onset of lay the plasma concentrations of LH and the rate of lay were similar in hens maintained under a long photoperiod (16L:8D) and a short photoperiod (8L:16D) supplemented by 1- or 10-min pulses of light at hourly intervals. In each of these groups the parameters measured were significantly ( P < 0.02) greater than in hens exposed either to an uninterrupted short photoperiod (8L:16D) or to the photoperiod on which was superimposed 10-sec pulses of light. The increased plasma concentration of LH and rate of lay observed in hens kept on a long photoperiod (16L:8D) were associated with an enhanced LH response to progesterone compared to that measured in hens exposed to 8 hr light per day.