Factors related to free-range use in commercial laying hens

Free-range use is expected to contribute to the welfare of laying hens, and more so if a high proportion of the hens in a flock uses the range. In the Netherlands and Switzerland, data were collected about free-range use, genotype, rearing conditions, housing system, management, performance, health, welfare and behaviour in 169 free-range and organic layer flocks by farm visits at an age between 45 and 66 weeks. The aim of this study was to identify which factors are related to free-range use. We analysed the % of hens seen outside when conditions for ranging were optimal (% Hens Out). Based on literature and expert knowledge, 26 potential correlating factors were subjected to preselection. Pearson correlation, independent samples t-tests and one-way ANOVA's were performed to investigate correlation between the factors and % Hens Out one by one. Twelve factors appeared to be related significantly to % Hens Out and these were entered in a linear regression model: country, production system, genotype, flock size, stocking density, presence of roosters, feather damage, keel bone damage, health at 60 weeks, outside access during rearing, type of ventilation, and amount of daylight in the house. The final model for the total sample explained 47% of the variation in % Hens Out and contained 5 variables. A higher % Hens Out was associated with brown genotype, smaller flock size, roosters in the flock, better feather cover and natural ventilation. Further analyses were done with subsets of the database for either free-range or organic flocks in either the Netherlands or Switzerland. No factors could be found that explained % Hens Out in Dutch free-range flocks. A better feather score and higher amount of daylight explained 44% of the variation in % Hens Out in Dutch organic flocks. Roosters and rearing on the laying farm explained 41% of the variation in % Hens Out in Swiss free-range flocks. Les fearfulness and brown genotypes or more than one genotype per flock explained 33% of the variation in % Hens Out in Swiss organic flocks. The results may contribute to improving range use by laying hens.