I was reading "Hog Ties" and came across an interesting bit about pigs.
When humans aren't around, pigs spend 95% of the time lying down, because there's no reason to get up. They've got food and water. If they've been neutered, they have no interesting in mating other pigs. There's just no reason to get up.
Another neat bit: pigs train humans to come in an clean their feeders, so they can "play" with the humans.