hundreds of pigs spawn everywhere, and wont go away even when world is reloaded

When I loaded my world, I noticed that chunks were loading slowly. Because of this, I could see through the walls of my house. I saw that hundreds of pigs had spawned outside, near the lingering chunk error that won't go away. I reloaded the world, but they didn't despawn. I couldn't move at all, due to all of the lag.