Noises are cut short when to many cows are bred

The problem is that noises are being cut short when there are to many cows i have bred. the sound is only cut short in the chunks near the cows.

I expected to be able to hear a full MOOOO sound when the cows are in the pen. but i only hear the MM part of it for about maybe half a second.

Steps:
1. Get cows in a breeding cell of some kind.
2. continually breed the cows with wheat until there are about 70 cows.
3. listen to the sound effects while standing near the cows.