How does red light affect layer production, fear, and stress?

Light-emitting diode (LED) light bulbs are becoming more prevalent in layer production as unlike CFLs they are dimmable and are even more energy-efficient than CFLs. There is also discussion on whether the spectrum of light that is produced by the bulb can affect production, stress, and behavior of laying hens. To investigate if differences between how the bulb that produce different wavelengths of light affect these factors, we raised White Leghorn hens under either a bulb that produced white light with the addition of red light (Once, Inc, AgriShift MLL; RED) or a bulb that produced only white light (Overdrive, L10NA19DIM 3000 K; WHITE). Each treatment consisted of 36 White Leghorn hens, and the experiment was replicated three times for a total of 108 hens per treatment. Production parameters including % hens in lay, feed conversion, average egg weight, total eggs per hen, eggshell breaking strength, and Haugh units were measured. Hen fear response during tonic immobility and inversion was documented at 3 time points during the study (18, 42, and 72 wk of age). Stress susceptibility was also quantified using plasma corticosterone, heterophil to lymphocyte ratio, and composite asymmetry score at the same time points as the fear testing. No production parameters were affected by lighting type (P > 0.05). Lighting type did not affect tonic immobility or inversion response (P > 0.05). By 42 wk of age and continuing on until 72 wk of age, the RED treatment had lower plasma corticosterone concentrations, lower heterophil to lymphocyte ratios, and lower composite asymmetry scores than the WHITE treatment (P < 0.05). The results indicate that including red light in the spectrum of light layers are reared under can lower stress susceptibility but had no effect on fear response or production parameters when compared to white light.