Effects of ultraviolet light supplementation on hen behaviour and welfare during early lay

Poultry can see in the ultraviolet (UV) spectrum and supplementation of UVA has been shown to reduce laying hens' fear and stress. The shorter wavelengths (UVB) also facilitate vitamin D3 production. However, UV spectrums are typically not included in indoor commercial poultry lighting which may result in less than optimum welfare of laying hens. This study predicted that UVA and UVA/B supplementation would increase desirable behaviours such as foraging and exploratory pecking and reduce measures of fear and stress. The effects of UV light supplementation were assessed on 252 ISA Brown hens during the period from 16 to 27 weeks of age. Birds were housed in eighteen pens (14 hens/pen) under three different light treatment groups each with six replications: (i) UV0: standard control lighting with LED white light, (ii) UVA: control lighting plus a supplemental 'daylight' avian bulb providing UVA, and (iii) UVA/B: control lighting plus a supplemental full spectrum reptile bulb containing both UVA and UVB wavelengths. Time budgets were assessed in the home pens at 18 and 24 weeks. At 20, 23, and 26 weeks assessments included: individual behavioural tests of tonic immobility and open field, pen-level novel object tests and blood heterophil/lymphocyte (H/L) ratios. At 27 weeks the UV supplemental lights were turned off for 3 days as a 'stressor' with bird locations in the pen measured before and during the stressor, along with H/L ratio and attention bias test assessments. Results showed limited effects of the supplemental lights. At 26 weeks both UV light treatments reduced tonic immobility duration (P = 0.006) and vocalisations across time in the open field test (P = 0.0003), while the UVA/B hens had lower H/L ratios than the UV0 hens (P = 0.01). However, removing the treatment lights did not result in greater stress and anxiety and there were few differences observed in the home pen time budgets. Overall, these results align with complementary findings in the same birds showing minimal impact of the UV treatments on measures of egg production, egg quality, bone health, and circulating plasma P and Ca but with an increase in serum vitamin D (25(OH)D3) for the UVA/B hens. The supplemental UV lights in this study were only on one side of the pens which could have minimised their impacts. Similarly, effects may vary at different points in the production cycle than included in this study.