In addition to the milk, this cream also contains collagen and hyaluronic acid to create a barrier and prevent moisture loss. All in all, some pretty serious awesomeness in this humble little tube. 
Well, donkey milk is a very rare and hard to come by ingredient. Its only available for six months out of the year and even then, you can only collect less than 1 liter a day from each mama donkey. Its also the milk that is the closest in composition to human milk, their PHs are nearly identical. Human milk has a PH of 7.0 7.5, donkey milk sits at 7.0 7.2! Donkey milk is also full of both omega 3 and omega 6 fatty acids. Its also very rich in lactose so its extremely hydrating and nourishing to skin. Its been used since the dawn of civilization in Egypt, Rome, and Greece so this is nothing new. Hell, Cleopatra herself used to take donkey/ass milk baths to preserve her beauty.