Animal welfare aspects of outdoor runs for laying hens: a review

This review discusses animal welfare effects of providing an outdoor run to laying hens. Compared with barn systems, the provision of an outdoor run leads to higher space allowances, a higher number and diversity of behavioural and physiological stimuli, and freedom to change between different environments with for instance different climatic conditions. Evidence is presented that these factors may have positive welfare effects for the hens, although, due to the complex interaction with other factors, this is not necessarily always the case. Outdoor runs may, at the same time, impose increased welfare risks associated with an increased contact with infectious agents, greater difficulties to maintain good hygienic standards, possibly imbalanced diets and predation threats. Measures to limit these welfare risks and to take full advantage of the potentials of outdoor runs include restriction of group size, keeping cockerels with the hens, hygienic measures including rotation of runs, providing well-dispersed covers, as well as appropriate pullet rearing and breeding strategies. Fully mobile housing systems provide a promising integrated approach to concurrently implement a number of effective measures. However, it is concluded that too little research and not enough resources went into solving the problems presently besetting free-range systems and that it, therefore, would be premature to make a final judgement now on welfare effects of outdoor systems in comparison with pure indoor systems.