We’re all familiar with the storybook image of a cat lapping up a bowl of milk. Cats probably first developed a taste for cow’s milk from hanging out in dairy barns, where milk was a coveted treat. What was not to like about this rich and vaguely sweet substance? But milk is not a natural part of an adult cat’s diet, and in some cases it’s not good for them.

Cats may like milk, but milk doesn’t always like them. This is because like some people, many cats are lactose intolerant. This means they lack sufficient quantities of a special enzyme called lactase to digest lactose, the sugar found in milk. Undigested sugars cause havoc in the intestines, including gas, cramping, and diarrhea.

Lactose intolerance is a fact of life for most adult mammals. Baby animals have lactase in their intestines to digest their mother’s milk. But once they are weaned, lactase levels drop. This isn’t a problem in nature, because adult animals would have no reason to drink milk. In our domesticated world, cats drink milk because we offer it to them.

Cow’s milk is never OK for kittens. While young kittens can handle the lactose just fine, cow’s milk lacks many of the essential nutrients, protein, and antibodies a growing kitten needs. Kittens should drink their own mother’s milk if at all possible. If not, they should be fed a milk replacer formulated especially for kittens, available at most pet stores.

If you still want to give your adult cat milk, but don’t know if he or she can handle lactose, try the following. Offer your cat 1-2 tablespoons of cow’s milk and monitor over the next 12 hours. If no tummy troubles develop, then your cat can safely drink milk as an occasional treat. But do so in moderation. Treats, including milk products, should not comprise more than 5-10% of a cat’s regular diet. Cow’s milk should never be a cat’s primary food source because it lacks essential nutrients.

If your cat is lactose intolerant, but enjoys milk nonetheless, there are several options you can try. Plain yogurt usually contains less lactose and may be better tolerated than milk. Lactose-free milk from the supermarket can often work well. The jury is still out on soy milk (see box). Another option is a feline milk substitute called Catsip. This product is made from lowfat milk with lactase added to help digest the milk sugar.

Remember that milk is a treat, and never a substitute for proper nutrition. For more information on milk and other appropriate treats for your cat, it’s best to consult with your veterinarian.