Despawning of tamed mobs

Bascily when I play Minecraft I have a ton of horses, then I leave or even in my house, they despawn somehow. It's getting annoying and I lost many saddles :| . Some mobs I have in my house, like 8 pigs despawned and new ones keep doing the same. I had a donkey on a leash, go ne, a horse with a saddle in my house, gone, a donkey with a saddle on my house...gone, and they keep despawning. PLEASE FIX THIS GLITCH!!!