In the European Union, pregnant sows in intensive farming systems are mostly kept in groups but for short period of time also individually. In each of these two housing systems, there are a number of factors that can negatively affect the mental and physical state of sows. The objective of our work was to critically evaluate the effects of individual and group housing on the welfare of pregnant sows. In individual housing, sows are most likely to suffer physical injuries to the skin due to prolonged pressure on body parts. Sows are severely restricted in their freedom of movement and are hindered in standing up, lying down or assuming comfortable positions while lying. In group housing, some sows may suffer from aggression from higher-ranking conspecifics. They may be deprived of access to resources such as feed, water and resting areas. In intensive housing systems, sows often live in a poor environment that does not meet their ethological needs. This can lead to aggression, abnormal behaviour, health problems and reduced production. Pigs have a strong exploratory instinct that can be satisfied by enriching the pen with straw. Because pigs are social animals, group housing best meets their needs for social behaviour. However, care must be taken when grouping pregnant sows together, as any aggression can result in physical injury and possible embryo loss. Sows have a poor ability to thermoregulate, so in the wild they help themselves with their characteristic behaviour, wallowing. In stable however, this behaviour is not possible, so we need to pay special attention to appropriate temperature. Air quality and the amount of light also have an important influence on health.
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