Genius. Although, even if the barn walkers were there while the herd passed through, the group would still have to leave the farm.

 

I doubt it. The Greene's and their neighbors were farmers, and each family must of had a lot of acreage. I think when the walker virus hit their community, those who weren't bit either fled the area or went to the aid station at the high school, only to die when it was overrun.

 

If walkers dont come to an area from a distance because other walkers are already there, how do herds and mega herds occur? Also why would walkers continue to swarm around the prison (or any area for that matter)when many other walkers were already there? I dont think walkers repel other walkers, I think they masked the fact that Michonne was living. I agree with Rapscillion that it was because farm was isolated. The stray walker that came by would bump into a fence preventing it from getting to farmhouse and eventually meander until it got caught in the swamp where Otis would collect it. The herd might have passed by but for a gunshot that attracted them.