Cats should not have cow's milk. Most cats are lactose intolerant, meaning they lack the enzyme needed to digest lactose, the sugar in milk. Drinking cow's milk can cause them digestive issues like vomiting, diarrhea, and stomach pain. Additionally, cow's milk is not nutritionally suitable for cats and can unbalance their diets, potentially leading to obesity and other health problems. Kittens only need their mother's milk or specially formulated kitten milk while nursing; adult cats do not require milk at all. If milk is given, it should be lactose-free or specifically designed for cats, and only as an occasional treat, not a regular part of their diet.