Sobotik, E. B., Nelson, J. R., Archer, G. S. 2020. How does ultraviolet light affect layer production, fear, and stress. Applied Animal Behaviour Science 223, 104926.

The lighting spectrum used in modern poultry production commonly lacks significant amounts of ultraviolet light; however, poultry can perceive the ultraviolet spectrum unlike humans and little research has been done to investigate the importance of this part of the spectrum on bird welfare. To determine if adding ultraviolet light to typical light emitting diode (LED) lighting affected production, stress, and behavior we reared laying hens from 18 to 72 weeks of age under either just a commonly used LED fixture (Control) or with the addition of ultraviolet light (UV). To determine stress bilateral asymmetry (ASYM, n = 216), humoral immunity (KLH, n = 40), heterophil to lymphocyte ratios (HL, n = 24), and plasma corticosterone concentrations (CORT, n = 24) were measured. Fear was measured using tonic immobility (TI, n = 216) and inversion (INV, n = 216 during production. Production traits and egg quality traits were also determined. The UV birds had lower CORT at 44 and 72 weeks of age (448.5 ± 70.5 ng/dl, P = 0.03; 1433.0 ± 163.4 ng/dl, P = 0.05), ASYM (4.39 ± 0.23, P = 0.03; 3.22 ± 0.18, P = 0.004) and HL (0.28 ± 0.02, P = 0.002; 0.31 ± 0.03, P = 0.02) at 44 and 72 weeks of age than the Control birds (699.4 ± 89.9 ng/dl; 1840.7 ± 124.5 ng/dl, 5.26 ± 0.33; 4.06 ± 0.22 and 0.41 ± 0.03; 0.42 ± 0.04). The UV birds righted faster during TI (299 ± 17 s, P = 0.05; 306 ± 19 s, P = 0.04) and flapped less intensely during INV (5.35 ± 0.17 flaps/sec, P = 0.04; 5.09 ± 0.17 flaps/sec, P < 0.001) compared to Control birds (347 ± 17 s; 361 ± 19 s and 5.90 ± 0.20 flaps/sec; 5.78 ± 0.13 flaps/sec) at 44 and 72 weeks of age. There was no difference between treatments in KLH, egg shell breaking strength, egg shell puncture strength, egg shell thickness, haugh unit, feed conversion, and average egg weight at any of the time points (P > 0.05). These results demonstrate that rearing laying hens with UV light as part of the lighting spectrum can reduce their stress and fear response and once again indicate that it is important to use the correct lighting to optimize bird welfare.