As we studied how finisher pigs perform in large groups we have also studied their eating behaviour. Our reasons for this extend beyond our interest in feed intake, to questions we have on how pigs perceive their environment and the impact that could have on our management. For example, when we first started working with larger groups, in this case 80 pigs in a pen, two theories existed for how pigs interacted with this large space. One theory was that to avoid unfamiliar pigs and aggression, the animals would restrict their movement to a limited area of the pen. We would call this a territory. We used 8 feeders in the pen of 80 pigs, and spaced these evenly along one of the long walls of the rectangular pen. Of 60 pigs that we observed, 80% visited all 8 of the feeders during a 24-hr period. All of the pigs ate from at least 6 of the feeders. This eating behaviour demonstrated that the pigs were not territorial, but used the entire pen. The implication was that resources, such as feed and water, did not have to be located throughout the pen, but could be concentrated, perhaps in a food-court.
We continued our studies with slightly larger groups (108 pigs/pen) but retained the spacing of feeders equidistantly along the length of the pen. The eating behaviour of pigs in large and small (18 pigs/pen) groups was remarkably similar with the exception of the first week after group formation. While pigs in large and small groups spent similar amounts of time eating during the first week, those in large groups visited feeders more often (35 times/day) than did those in small groups (25 times/day). As with the pigs in the previous study, the pigs in large groups were sampling many feeders each day. The first week after the groups were formed we saw both a reduction in average daily gain and an increase in feeder visits (but not total eating time) in large groups compared to small. We hypothesize that the need to investigate the entire pen during the first days in a large group led to many feeder visits, and contributed to a reduction in growth.
Moving on from our finding in the first study that pigs would use the entire pen, our next experimental set-up placed the feeders in the large group together near one end of the pen. Unlike the previous studies, pigs in the large group would have to travel farther from their lying area to the feeder than did the pigs in small groups. The eating behaviour of pigs in large groups changed. When the cost (effort) to get to a resource (feeder) increases, we would predict that animals would visit the resource less often, but the visits would be longer to compensate. This is what we saw in large groups. The pigs in large groups ate fewer (9.2 vs 11.7 meals/day) but longer meals (7.4 vs 5.3 min/meal), so that the total time spent eating in a day (60.4 vs 55.7 min/day) and total feed intake (2.78 vs 2.82 kg/day) were similar in large and small groups. In this same study we superimposed a crowded treatment (k = 0.025) on the group sizes. Crowded pigs also reduced the number of visits to the feeder each day, but they did not increase the length of their visits or maintain their total eating time and feed intake. The crowded pigs demonstrated a loss of appetite compared to the pigs in large groups, even though both conditions resulted in fewer meals.
Our studies on eating behaviour of pigs in large groups have demonstrated that pigs make use of the entire pen, visiting most if not all feeders regularly. The inquisitiveness leading to this extensive use of the pen is evident in a large number of feeder visits during the first week, and may contribute to poor initial growth in the system. When feeders are concentrated in one area of the pen, making it more difficult to get to a feeder, pigs in large groups reduce their number of meals, but compensate by having longer meals. The adaptability of pigs in large groups allows us to broaden the scope of our management options to include not only large groups, but also concentrated feeding areas within the pen.