From children's books to TV commercials, the idea that cats are wild about milk is constantly reinforced. Yet what pop culture fails to show is what happens shortly after that bowl of milk is empty. The cute kitty peacefully lapping away at a bowl of fresh milk is likely to spend the next few hours suffering from diarrhea, gas, bloating and other unpleasant side effects.
Cats, like most adult mammals (including the majority of humans), are lactose intolerant [source: Cornell University College of Veterinary Medicine]. That means they lack the enzymes needed to break down lactose, or sugars found in milk. A bowl of milk isn't likely to be deadly, but the aftereffects are likely to trouble both the cat and the owner who's forced to clean up the mess.
If your cat seems to tolerate milk to an extent, or you simply want to offer your cat something special, consider milk like any other treat. Since milk has little nutritional value to the cat, it's no substitute for proper cat food, and should be served to the cat with the same care that you would any other human foods or commercial cat treats. That means making sure that milk and other treats make up only 10 to 15 percent of a cat's diet [source: Cornell University College of Veterinary Medicine].
To prevent obesity, consider limiting milk to no more than 20 to 30 calories per day [source: Zelevansky]. Since a cup of skim milk weighs in at 83 calories, give your cat no more than a few spoonfuls to avoid potential weight problems. Consider lactose-free milk or goat's milk to reduce digestive problems.
So what about kittens? Surely they need milk, right? While kittens have the ability to digest some lactose, their bodies simply aren't designed to deal with the level of lactose found in cow's milk, which has about three times as much lactose as that of a momma cat [source: Wortinger].
Drinking regular milk will not only give kittens diarrhea, but will also cause them to slowly starve to death if their diet isn't properly supplemented [source: Kitten Rescue]. The ratio of caseins and whey in cow's milk is nowhere near sufficient to support a growing kitten [source: Fries]. If you're attempting to nurse kittens without the help of mom, pick up special cat's milk at the pet store. This "milk" is specially formulated to provide the right ratio of caseins and whey to meet the nutritional needs of kittens without the painful digestive issues associated with cow's milk.