I read something about lactose intolerance recently (I forget where). Apparently lactose intolerance in adult mammals is the norm, and humans are unique in having evolved a digestive system which tolerates milk. All other mammals have digestive systems which have an override which enables them to accept mother's milk as babies, but the override is normally switched off when they become adults. Because of normal variations, some humans do become lactose intolerant, and some other adult mammals do not.
In some cases, lactose intolerance is a life threatening condition. Those kind but unaware people who put out bread and milk for hedgehogs are sadly endangering their lives.