Despawn-safe Mobs Despawning

I have a large (90 MB) world that crashes frequently. While the crashes are annoying, I am fine with dealing with them, but they often wreak havoc on my world, most notably deleting mobs that should under no conditions despawn.

Thus far, two tamed and saddled horses, one saddled and previously fed pig, and one named slime have despawned. I am certain this is happening during the crashes, as I received no death messages for the horses, and I was next to the slime when my game crashed and when I logged back on, it was gone.

While I am aware that crashes are a seperate issue, I ask only that you minimalize the effects of crashes (if possible). There will always be crashes, but it would be much appreciated if the worlds crashing were not affected.