Research conducted at the Prairie Swine Centre shows pigs raised in very large groups tend to be far less aggressive than those raised in small groups.
Over the past decade the Prairie Swine Centre has conducted a wide range of research looking at the dynamics of group housing including such things as the impact of group size on social behavior and aggression. Dr. Harold Gonyou, a research scientist in animal behavior, says pigs seem to learn from their social environment how they should react socially.
Dr. Gonyou speculates that somewhere between 50 and 100 pigs per pen is where he starts seeing a difference in the social behavior of the pig. In his experience, they become more socially tolerant, less willing to fight if housed in larger groups. He says this pays dividends later on when the pigs are mixed during loading and transport to market.
Source:
Farmscape.ca, April 4, 2007
http://www.farmscape.ca