Review: Space allowance for growing pigs: animal welfare, performance and on-farm practicality

There is considerable variation in the recommended minimum space allowance for growing pigs in scientific literature, and growing pressure, arising from recent reviews of current animal welfare standards for pigs, to increase the minimum space allowances set in legislation in some countries (e.g., European Union countries and New Zealand). The space provided for growing pigs needs to accommodate their physical body size in addition to social behaviour, activity, and essential functional behaviours. However, recommended minimum space allowances vary according to criteria such as temperature, live weight, flooring type, group size, behaviour, and enrichment availability. Though there may be justification for increasing current space requirements, this will present a practical issue on existing farms and could even result in unintended negative welfare outcomes, depending on how farmers address an increased requirement for space. This is not helped by inconsistent scientific approaches to assessing the effect of space on pig performance, and a lack of information on how space allowance impacts a pig's affective state. This review explores the scientific basis of the most common approaches to determining minimum space allowances for growing pigs and discusses the various factors that influence and interact with their spatial requirements. Consideration is given to their nutrition, physical environment, health, and behaviour to understand the welfare, performance, and practicality implications of differing recommendations for space allowance. More research is needed that investigates a range of space allowances to better understand the relationship between animal welfare and performance outcomes, and space allowance. This must replicate commercial conditions so that recommendations are relevant, future-focused, and achieve positive welfare outcomes in a practical but meaningful manner.