Normally, when you load in your map and you have Animals fenced in, you expect them all to be alive and accounted for.

What has instead been happening is that I'll start up my map, and I'll hear the sound of certain animals being hurt rather quickly. I'll then go to their fenced off area and find dead live stock laying around.

Steps to Reproduce:
1. Make a fenced area, and start spawning one of any of the farm animals: Cows, Pigs, Sheep, Chickens, or Horses.
2. Wait for some of the selected animals to crowd around one corner of the fenced area
3. Leave the world, and load it back up.

This also works if you go into the Nether, and come back in.