Relationship between sunlight and range use of commercial free-range hens in Australia

In Australia, summer brings intense, bright sunlight with high ultraviolet (UV) radiation and hot temperatures, which might impact free-range hens' ranging outside. To determine how range use was correlated with different sunlight variables and weather factors, a study was carried out on three commercial free-range layer farms during the summer/autumn period (December-May) across diverse regions of Australia in Tasmania (TAS), Queensland (QLD), and Western Australia (WA). Hens' range distribution was determined by counting the number of hens in the direct sunlight ('sun') or 'cloud' and shaded areas ('sun-shade' or 'cloud-shade', in sunny or cloudy conditions, respectively) using image snapshots taken at 30 min intervals from video recordings of a portion of one shed comprising 20,000-30,000 hens on each farm during the production phase of the laying cycle. The solar radiation spectrum [UV radiation (UVAB) (288-432 nm), photosynthetically active radiation (PAR; visible light) (400-700 nm), and total solar radiation (TSR) (285 nm-3000 nm)] and weather data (ambient temperature and relative humidity) were recorded through an on-site weather station. Data were analysed separately due to discrepancies between the farms' layouts. The effects of time of day and months on range use were analysed using General Linear Models in JMP® 16.0 and the relationship of sunlight and weather variables with hens' distribution in 'sun'/'sun-shade' and 'cloud'/'cloud-shade' in sunny and cloudy conditions respectively was determined by fitting linear ridge regression models using the 'lmridge' package in R. Overall, the time of day and month had significant effects on hens' distribution on the range (all p < 0.0001). Hens' range occupancy in the 'sun' decreased during the midday period with gradual increases in the late afternoon to evening, and the opposite pattern in the 'sun-shade'. A linear increase in the number of hens on the range over the months indicated the seasonal effects on hen ranging patterns. Temperature, UVAB and PAR were the most important factors for discouraging hens' range use in the 'sun' suggesting free-range systems in Australia should be designed to account for the extreme sunlight using adequate shade for optimum ranging across summer.