Mob Rebirth Mod 1.8, 1.7.10, 1.7.2 is a mod that makes it so when mobs die, there is a chance that it will be 'reborn'. You can configure most features of the mod, including whether 'rebirth' means dropping the spawn egg or spawning another of the same mob in its place, rebirth chance, whether animals can be reborn, and whether mobs can die from anything or just being killed by the player.
Note before downloading: This mod requires Mob Rebirth Mod 1.8, 1.7.10, 1.7.2