After spawning a certain number of chickens and killing cows,pigs, and sheep. The cows,pigs and sheep stop spawning

Put the summary of the bug you're having here
After spawning a certain number of chickens and killing cows,pigs, and sheep. The cows,pigs and sheep stop spawning
What I expected to happen was...:
I couldn't get more meat

What actually happened was...:
Describe what happened her

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...spawn about 10 chickens
3. ...then kill other neutral mobs