Arousal and exploration in growing pigs in different environments

Abstract

Under modern husbandry, pigs are likely to be severely frustrated because (generally) fattening pigs are kept in mono-cast groups in very bare pens. From a comparison with semi-natural conditions, it can be seen that many important social and non-social external stimuli which are important in releasing and orienting many behaviour patterns are lacking. Various consummatory acts may therefore be impeded and the animals’ appetitive behaviour patterns remain unfulfilled. To assess the degree of behavior& restraint of growing pigs housed intensively, their reactions in different environments towards an unfamiliar object were compared. In each of 4 different environments, five sets of lo-14 growing pigs aged 4-6 months were presented with a hanging tyre close to their nest. The trials, in which the pigs were tested as a group, lasted up to 80 min and were repeated on different days. The environments were (1) an indoor Danish pen with a concrete, partially slatted, floor, (2) a straw-bedded open-front pen, (3) an enriched pen with straw bed, yard part and various furnishings, and (4) a large semi-natural wooded enclosure, where the juveniles were in families with adults and sub-adults. The barer the environment, the more strongly the group reacted towards the stimulus. Strong reactions to the tyre were seen in the first two environments after 80 min, lasting up to 28 and 72 min, respectively, before the tyre was left untouched for 30 s, while in the semi-natural enclosure, no attention was paid to the tyre in any trial after 10 min and in the enriched pen in any trial after 30 min. The mean proportion of animals of a group reacting towards the stimulus during the group reaction time was significantly greater the barer the environment. In addition, significantly more aggressive interactions were observed towards the tyre in the barer environments. An essential quality of the exploratory reaction is the inclusion of behavioural elements from many different functional systems that normally do not occur in juxtaposition, and such sequences of behaviour were seen in the pigs’ response. Interest in the tyre started with investigative sniffing, followed mostly by aggressive elements or by nosing or chewing. Whereas courtship elements were rarely shown, the significantly most frequent transitions in the behavioural sequence led to material gathering and nest-building and then to comfort behaviour or to marking behaviour. Marking, displacement and nosing were significantly more frequent at the end of the reactive sequence than other behaviour patterns. Therefore, the pigs seem at first to test what the tyre can be used for, and then often (seem to) take possession of it, before they put it aside.