Put the summary of the bug you're having here

What I expected to happen was...
For the animals to stay in the pen

What actually happened was...:
i put 8 cows, in one pen, 8 pigs in another pen, 8 sheep in another pen and 8 chickens in another. I also had a few horses in another pen. i left to go map and came back to 5 cows left in the pen, 6 pigs left in a pen, and almost all the sheep and chickens gone, and all the horses free.

Steps to Reproduce:
Put more animals in a pen than should really fit, leave chunk and let it despawn, come back and the animals should be out.
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