The effect of group housing on feeding patterns and social behaviour of previously individually housed growing pigs

Abstract

Group housed pigs make less frequent feeder visits of longer duration, and eat at a faster rate than pigs housed individually. They also have lower growth rates which may be due to elevated stress levels resulting from changes in the concentrations of hormones, such as cortisol and adrenaline associated with aggression and social stress. The aim of this experiment was to investigate the effects of grouping on feeding pattern, time budgeting and the social behaviour of pigs kept as individuals from weaning until grouping. In total, 12 Large White×Landrace male pigs (four pigs per block) mean (±S.E.) start weight 22.5±0.7 kg were housed individually for 3 weeks (Period 1) after which in two replicates (Blocks 1 and 3), pigs were combined into a group of four (Period 2) before being returned to individual housing for a further 3 weeks (Period 3). In Block 2, the four pigs remained as individuals across periods but were moved between pens at the end of Periods 1 and 2 to account for any pen effects. Feeding pattern and food intake were recorded throughout and pigs were weighed three times a week. Video recordings and live behavioural observations were made to record time budgets and social behaviour. Grouped pigs made less visits to the feeder in Period 2 than when they were housed individually in Periods 1 (P<0.001) and 3 (P<0.01). Visit duration was longer in Period 2 than in Periods 1 (P<0.01) and 3 (P<0.05). Food intake and weight gain were greater in Period 3 than in Periods 1 and 2 (P<0.001 and P<0.01, respectively). There were no significant effects of moving pigs between pens in Block 2 on feeding behaviour and timebudgets. In Period 2, grouped pigs slept more (P<0.01) and spent less time feeding (P<0.01) and rooting (P<0.01) than in Periods 1 and 3. The frequency of aggression decreased over time from mixing (P<0.001). Possible explanations for the changes in feeding behaviour when pigs are moved from individual to group housing are competition, group cohesion, or that the high frequency of feeder visits when the pigs are housed individually is a consequence of a lack of social stimulation. Of these different possibilities, the results suggest that group cohesion is most likely to have been causal in the observed changes in feeding behaviour.

Introduction

Normal farming practices require that growing pigs are frequently grouped and mixed, for example, at weaning, at the start of finishing, during transport and at lairage. This results in a disruption of social organisation which can lead to an increase in aggression (Meese and Ewbank, 1973), and social stress (Hessing et al., 1994), which in turn can compromise welfare and growth. Moreover, differences between pigs kept as individuals and as groups have been reported in terms of feeding behaviour. It has been found that group housed pigs modify their feeding behaviour by eating less frequently, consuming more food at a time and at a faster rate compared to pigs housed individually (de Haer and Merks, 1992). In addition, pigs in individual housing have higher digestibility coefficients related to smaller, more frequent meals as described by de Haer and de Vries (1993). In terms of production parameters, the latter authors found that group housed pigs had significantly lower growth rates, and less back fat than pigs housed individually. Furthermore, Gonyou et al. (1992) found that pigs housed individually gained more weight and had a higher food intake than pigs housed in groups of five.

Competition at the feeder, social facilitation, and social stress are all factors that may be responsible for the differences in feeding behaviour and production parameters between group housed and individually housed pigs. Social facilitation in group housed pigs results in synchronised feeding, but can lead to increased competition for feeder space in pigs kept in groups, caused by the motivation to feed simultaneously. Therefore, a balance between the amount of competition and the amount of social facilitation that occurs in a group situation must be found if the maximum food intake is to be achieved (Hisa and Wood-Gush, 1983). In addition, neophobic responses to unfamiliar pigs and environment when mixed may also play a part. Indeed, Tan et al. (1991) found that merely moving pens of pigs, without mixing, also resulted in a decline in productivity.

Although, there have been studies on the differences in feeding behaviour between group housed and individually housed pigs, there are few reports in the literature of experiments where the two housing regimes have been imposed on the same pigs. Nielsen et al. (1996a) found that group housed pigs did not greatly alter their feeding behaviour when they were subsequently individually housed, suggesting that feeding behaviour in pigs was not as flexible as previously postulated. However, the pigs were housed individually after a period of grouping, and it would be useful to ascertain the effects of grouping after an initial period of individual housing which would allow individual pigs’ feeding patterns to develop in an unconstrained way.

The aim of the present experiment was to investigate the effects of grouping on feeding pattern, time budgeting and the social development of pigs kept as individuals from weaning before grouping. This was achieved by housing pigs individually from weaning with ad libitum access to food to allow them to develop their preferred feeding patterns. Following this, individuals were mixed into groups of four pigs. Finally, the pigs were returned to their individual pens. By comparing feeding patterns between periods of the experiment, and studying the development of social behaviour within the groups, we investigated the effects of grouping on individual pigs. In addition, possible causal factors for differences in feeding patterns between individually and group housed pigs might be found.