Broilers' free range use is affected by vertical panels, age at first outdoor access, and weather conditions

In chickens with free-range access, often only part of the animals go outdoors and they usually stay close to the barn. The aims of this study were to investigate the effects of vertical panels, age at first outdoor access and weather conditions on free-range use of slow-growing broilers. Chickens were housed in mobile stables starting from one week before they were allowed outdoor access (n=100 per stable, four stables in total). Each stable was placed centrally on a plot of which two quadrants consisted of open grassland and two of grassland with 30 parallel-placed vertical wooden panels (lxh: 2.5x0.6m). In each round (n=3; Feb-May, April-July, July-Oct), chickens of two stables were given outdoor access at 4 weeks of age, the other two at 5 weeks, both until 10 weeks. Temperature, relative humidity (RH), precipitation, wind speed and solar radiation were recorded. The number of chickens outdoor and their location were scored two days per week (morning and evening) by live observations. The effect of these factors on outdoor use was analysed using logistic mixed-effects-models with a random effect for stable. On average, 16.3% of the chickens were located outdoor at any given moment (range: 0-63.2%). Chickens used the free range less with increasing wind speed (P<0.001), RH (P<0.001), precipitation (P<0.001) and solar radiation (P<0.001). The distance separating the chickens from the stable increased with age (mean: 7 cm/day; P<0.001). This increase was more pronounced if outdoor access was given at 4 instead of 5 weeks of age (P=0.042). Broilers preferred quadrants with vertical panels as compared to open grassland (56.2% vs. 43.8%; P<0.001). This preference was not significantly influenced by climatic parameters. In conclusion, several weather conditions decreased outdoor use by broilers, while early outdoor access and vertical panels increased the use of the free range.