Research note: evaluation of humoral and delayed hypersensitivity responses in cockerels reared under constant light or a twelve hour light:twelve hour dark photoperiod.

Immature cockerels were reared under constant light [24 h light (L):0 h dark (D)] or a 12L:12D photoperiod in order to evaluate the effect of constant light on immunoresponsiveness. At 10 wk of age males were immunized with SRBC, with reimmunization occurring either 3 or 8 wk later. Animals reared under constant light had lower (P less than .05) anti-SRBC antibody titers than the 12L:12D males. Additionally, the pattern of the antibody response following secondary immunizations were different, with 24L:0D males exhibiting no increase in antibody titers between Days 3 and 9 postinjection. Delayed hypersensitivity responses of 24L:0D males were lower (P less than .05) than those of 12- or 16-wk-old 12L:12D males. Taken together, these results suggest that circadian light:dark cycles may play a role in modulating the immune system.