I had hundreds of pigs in a pen, and now most of them have climbed the walls and scattered all over the place. :(
There's a command to kill mobs in a radius, kill what you need and then respawn your swine :)
http://minecraft.gamepedia.com/Commands#kill
For example
/kill @e[type=Creeper,r=20]
Hehe, sorry. It's a joke. I think it was coded to only last through april 1st anyhow as i logged into my local snapshot map and i actually had meat in my inventory. :o