The Impacts of Colony Cages on the Welfare of Chickens Farmed for Meat

SIMPLE SUMMARY: Over 70 billion chickens are slaughtered globally each year. Almost all are meat breeds, typically housed in very large barns with a litter floor. Recently however, modern cage systems have been developed which provide very limited space and stack several tiers high. There is debate about the impacts of such modern cage systems on chicken welfare. Accordingly, we systematically reviewed studies assessing the welfare of meat chickens kept in either modern cage systems or littered barns. Overall, 23 studies were reviewed, and none of the experimental studies reviewed incorporated a full behavioural analysis. Therefore, significant concerns exist about the deprivation of natural behaviours in meat chickens kept in modern cage systems. Given the numbers of meat chickens globally that could be impacted by these modern cage systems, this is a major animal welfare concern. Instead of implementing such systems, research and development should focus on improving the welfare of meat chickens kept in littered barns. A full behavioural analysis—as included in gold-standard animal welfare assessments, such as the Welfare Quality Assessment protocols—should form a mandatory part of any future studies investigating the welfare impacts of housing systems on chickens. ABSTRACT: There is growing interest in keeping meat chickens in modern colony cages (CCs) rather than conventional litter-floor barns. Suggested welfare improvements for chickens in such systems include reduced bodily lesions due to lower contact with flooring contaminated with faeces and urine, due to slatted flooring and automated faeces removal. This systematic review sought to determine the animal welfare impacts of CCs using slatted flooring, in comparison to litter-based non-cage systems. Overall, 23 relevant studies were retrieved. From one perspective, the extant research appeared mixed. Fifteen (65%) of these 23 studies identified some form of welfare concern about slatted floors, and thus CCs. Yet, when considering actual welfare indicators assessed, the tallies generated in favour of each housing system were similar. Crucially however, there were incomplete behavioural welfare measures in 100% of the empirical studies reviewed. Accordingly, significant welfare concerns exist about CCs, centring around behavioural deprivation. Given that over 70 billion chickens are farmed then slaughtered each year globally, widespread implementation of CCs would create a major animal welfare concern. Instead of implementing such CC systems, research and development is recommended into improving welfare outcomes of conventional litter barns using different forms of commercially feasible enrichment. As a minimum, a full behavioural analysis, as detailed in the Welfare Quality Assessment protocols, should form a mandatory part of any future studies aimed at assessing the welfare impacts of housing systems on farmed chickens.