Rushen, J., de Passillé, A. M., Appleby, M. C. et al. 2014. Alone or together: A risk assessment approach to group housing. In: Dilemmas in Animal Welfare. Appleby, M. C., Weary, D. M., Sandøe, P. (eds), 169-187. CAB International, Oxfordshire, UK.

The question of whether it is better to house animals in groups rather than alone deals with the unresolved issues at the heart of animal welfare. In particular, we need to be able to rank different classes of threats to welfare (e.g. behavioural deprivation versus illness) on a single scale. In this chapter we discuss the risk assessment approach to animal welfare that is currently being developed and ask to what extent it helps in answering this question. Qualitative risk assessment has been used to compare group housing and individual housing for dairy cows, and the conclusions are that while the hazards of tie stalls are more serious than those for loose housing on deep straw, the high incidence of lameness in cows housed in free stalls can result in a greater overall risk to welfare than occurs in tie stalls. Thus, the details of the particular group housing used need to be considered. We also discuss whether a quantitative risk assessment is possible and conclude that, as yet, too little is known about the magnitude of different threats to animals' welfare, and there remains too much disagreement over the fundamental nature of animal welfare for this to be currently feasible.