Should my cats drink milk? Probably not.
Cats don't need milk in their diets after weaning, typically at 6 to 8 weeks old. Your feline friend may love milk, but that doesn't mean you should keep pouring milk into your cat's bowl.
While nursing, a young feline produces an enzyme, called lactase, that helps break down the sugar (lactose) in its mother's milk. As kittens grow up and no longer need mother's milk, lactase generation slows and eventually goes away completely. Without the lactase enzyme, the large molecules of lactose go through the GI tract undigested, drawing far too much moisture. What does that mean? Too much moisture in the lactose-intolerant cat will give your companion diarrhea. Be aware that cow's milk is nutritionally different than cat's milk, and that makes it hard for cats of any age to digest.