Few animal species drink milk after reaching adulthood. Since cats do not have the necessary enzymes to digest the protein lactose that is present in dairy, they can get diarrhea after drinking milk. The same goes for eating dairy products such as yogurt, cheese, and cottage; They all contain lactose and are thus not recommended. If you still want to give your cat milk, there are special milk products specifically tailored to cats, which do not contain lactose. These products are certainly not essential to a healthy diet, so you should think of cat milk as a tasty treat, rather than a nutritious meal.