Behavior How is herd behavior different?

[MamaGuinea]

I've got three sows, and am thinking of getting a fourth. I've seen it mentioned online that once you get to a quad, the "herd behavior" kicks in, and things are different. Not sure what this means though. How is herd behavior different? What can I expect?

 

[sallyvh]

I wouldn't consider there to be any real differences. I find my bigger groups are a bit more active because there's more activity in the cage, but that is about it. They still do everything a pair of pigs does.