Cats can drink milk, but there is a risk of lactose intolerance. Kittens can drink milk before weaning because their bodies produce lactase to digest the lactose in their mother's milk.
However, adult cats gradually develop a decrease in lactase, leading to lactose intolerance in milk and potentially causing symptoms such as diarrhea and bloating. Therefore, while some kittens may appear healthy after drinking milk, it is recommended to avoid giving adult cats milk for their health.
