I've been playing the same survival map for well over 24 human hours. Sometimes in peaceful mode, sometimes not. I originally killed all the animals, especially the sheep since I didn't have a bed or sheers, or because the wool was white and I wanted a respawn for other colours. They never came back. Cows/Chickens/Sheep/Pigs - I have 0 of them! I've tried closing/restarting the game, no luck. I have iOS6, FYI.