Lying down and rolling behaviour in sows in relation to piglet crushing

Piglet crushing remains a problem in crated sows and it is even more of a problem in loose housing systems. Most piglets are crushed when the sow moves from standing to lying or when she rolls over while already lying. This paper reviews lying down and rolling behaviours in sows and their association with piglet crushing in loose housing environments. Only little is known of the rolling behaviour, but the frequency of rolling may be affected by floor properties and fast rolling seems to be more riskful for the piglets than slower rolling. There is substantially more knowledge of the lying down behaviour. The lying down sequence is commonly divided into five stages. The speed of performance of these stages may be related to the risk of piglet crushing, e.g. flopping (the hindquarter drops quickly to the floor) is the most dangerous way the sow can lie down. In contrast, lying down by leaning against a surface rather than lying down in the open reduces the risk of piglet crushing, as does the performance of pre-lying behaviour and adequate sow responsiveness to piglets. The factors that may affect the speed and way of lying down (domestication, breed, muscular control, previous and current housing), pre-lying behaviour (piglet stimuli and space) and responsiveness to piglets (piglet stimuli, timing in relation to parturition, space and bedding) are discussed. The presented knowledge could be used in design and management of farrowing pens in order to reduce piglet crushing. However, several areas still require investigation. The aim of these investigations should be to encourage sows to use support when lying down, but also to make the few very riskful unsupported lying events as well as rolling safer for the piglets. This may be achieved though, e.g. increased knowledge of the motivational context of the various ways of lying down and rolling, development of attractive support features that sows will willingly use and determination of space requirements for the entire lying down and rolling complexes (i.e. pre-lying/-rolling, actual lying/rolling and responsiveness to overlain piglets).