The effect of increasing group size on the performance and behaviour of pigs between 4 and 10 weeks of age was assessed. The pigs were assigned to groups of ten, twenty, thirty, forty and sixty at weaning. There were eight groups of each size on the experiment giving one thousand, two hundred and eighty pigs in total. The groups were balanced for gender and weight and were randomised across litters. One four-space dry feeder and separate drinking bowl was provided per ten pigs in each group.
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Increasing group size did not have a significant effect on mean growth rate, feed intake or feed conversion ratio over the treatment period. However small pigs in groups of ten tended to show lower growth rates than small pigs in larger groups. It is suggested that large pigs dominate the feeder in groups of ten and make it difficult for small pigs to gain access to the feeder. The difference in growth rate between small and large pigs led to a greater within-group variation in weight in groups of ten than in larger groups.
Behavioural observations showed a lower demand for the feeder during off-peak periods in groups of forty or sixty pigs than in smaller groups. There were no differences between group sizes in the incidence of aggressive behaviour at the feeder. In all treatments there was a greater incidence of small and medium sized pigs at the feeder than large pigs, which may indicate a slower rate of eating among smaller animals.
The results of this study indicate that the group size of weaned pigs can be increased from ten to sixty animals without any adverse effects on performance or welfare as measured by aggression at the feeder. There may be benefits in increasing group size to twenty or more animals in order to reduce demand for the feeder and within-group weight variation. In addition, increasing group size to sixty animals will reduce building costs and provide more usable space per pig. However, the temptation to reduce stocking rate or to reduce the number of feeders with larger groups must be avoided.
Increasing group size did not have a significant effect on mean growth rate, feed intake or feed conversion ratio over the treatment period. However small pigs in groups of ten tended to show lower growth rates than small pigs in larger groups. It is suggested that large pigs dominate the feeder in groups of ten and make it difficult for small pigs to gain access to the feeder. The difference in growth rate between small and large pigs led to a greater within-group variation in weight in groups of ten than in larger groups.
Behavioural observations showed a lower demand for the feeder during off-peak periods in groups of forty or sixty pigs than in smaller groups. There were no differences between group sizes in the incidence of aggressive behaviour at the feeder. In all treatments there was a greater incidence of small and medium sized pigs at the feeder than large pigs, which may indicate a slower rate of eating among smaller animals.
The results of this study indicate that the group size of weaned pigs can be increased from ten to sixty animals without any adverse effects on performance or welfare as measured by aggression at the feeder. There may be benefits in increasing group size to twenty or more animals in order to reduce demand for the feeder and within-group weight variation. In addition, increasing group size to sixty animals will reduce building costs and provide more usable space per pig. However, the temptation to reduce stocking rate or to reduce the number of feeders with larger groups must be avoided.
An investigation into the influence of group size on the performance and behaviour of weaned pigs