CHICKENS WON'T STOP SPAWNING

[EmperorAustin]

I placed a few chickens in a single player world, they started breeding, and before long, literally TWO THOUSAND OF THEM have spawned. I can't even get near the horde without massive slowdown, so killing them all isn't really an option. I tried doMobSpawning false, t/killallmobs, t/killchicken, t/butcher, whatever and nothing has worked. Is this part of some obscure hexxit mod, or just a glitch?

 

Any help would be greatly appreciated because I can't even build on my world without being like a 100 blocks away.