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.

Governmental and industry representatives have repeatedly claimed that Aotearoa New Zealand leads the world on animal welfare, largely based on an assessment by global animal protection charity World Animal Protection (WAP). New Zealand’s leading ranking rested primarily on favourable comparisons of its animal welfare legislation with that of 50 other nations, within WAP’s 2014 Animal Protection Index. Unfortunately, however, review of welfare problems extant within the farming of meat chickens and laying hens, pigs, cows and sheep, reveals the persistence of systemic welfare compromises within most New Zealand animal farming systems. These are contrary to good ethics, to our duty of care toward these animals, to the wishes of domestic and international consumers, and to the interests of New Zealand’s animal production industries, which make an unusually large contribution to New Zealand’s national economy. Accordingly, and despite progress to date, this study finds that significant further resource investment and policy reform within the field of animal welfare are clearly warranted within New Zealand.