Animals tamed or bred are de-spawning after leaving and re-joining world

There has been multiple times that I have left my world, and all animals in my farm that I have bred/tamed have been removed. Completely, with no explanation such as a creeper blowing up or anything. This has been going on for a while, yet seeing as though there really has been no action to remove it, I request that you look into this. My iron golem, 10+ dogs, many many farm animals, horses, 4 cats, and even the villagers I have traded with have de-spawned.