Effect of dietary vitamin D3 and ultraviolet-B light on the behaviour and growth of broilers challenged with social isolation stress

Within intensive poultry production systems, broilers are reared indoors, at fast growth rates in controlled environments with little access to natural light, which together impacts the expression of natural behaviours. Birds can see into the ultraviolet spectrum and the provision of ultraviolet-B (UVB) light may support the expression of natural behaviour and endogenous synthesis of vitamin D₃ (vitD₃). Commercially, chickens regularly encounter stressors, and both the environment and diet can influence their response to stressors. This study was designed to compare the impacts of providing dietary vitD₃ at 4000 IU/kg (VitD) compared with provision via UVB light on the behaviour of broilers challenged with periodic social isolation stress. One-day-old Ross 308 broiler chicks (n = 192) were randomly allocated to non-isolated (control) and periodically isolated groups and were provided with either, additional dietary vitD₃, or UVB light, in a 2 × 2 factorial design. UVB lamps were provided in all pens (12% UVB D3 of 55 cm length, 24-Watt, 280–315 nm wavelength and 28.12 µW/cm2 intensity) but in the VitD treatment, there were filters to remove UVB. Behaviour was recorded from video footage using instantaneous scans measuring the number of birds engaged in each behaviour six times per day on 12 days spread across days 2–39, resulting in 72 scan samples per pen. Body weight was measured weekly and analysed to provide context for understanding the activity of broilers. Body weight was modelled using growth curves and poisson models were used to analyse behaviour, controlling for the number of birds visible in scans. Chickens performed less active behaviour when they had been periodically isolated. Chickens spent more time sitting inactive (and less sitting active) and sleeping when they received UVB light but were not isolated. Sunbathing was lower in isolation treatments compared to controls, but this effect was reduced when they received UVB lighting. The growth rate of chickens was highest in the isolation and VitD treatment and higher for VitD compared to UVB treatments. Higher activity on days 2 and 39 was associated with a lower growth rate. These results indicate some benefits of supplementation of UVB light in terms of observing natural behaviour when chickens are exposed to stressors. However, we did not observe large differences in behaviour in chickens receiving UVB light compared to those provided with VitD. Further research is needed to investigate the benefits and optimal level of UVB light to support the behaviour and welfare of broilers.