Kittens digest their mother's milk perfectly well, but production of lactase — the enzyme that breaks down lactose — falls away in most cats as they grow up. Undigested lactose stays in the gut, draws in water, and ferments, which is the recipe for diarrhea, bloating, and discomfort a few hours after that bowl of milk. Tolerance varies: some cats handle a splash without trouble, but you usually find out the messy way.
Milk also adds calories without balancing a cat's diet, so even a lactose-tolerant cat gains nothing nutritionally from it. If your cat genuinely loves the ritual, lactose-free "cat milk" sold in pet stores is the safer version of the treat, in small amounts. Kittens that need hand-rearing should get a proper kitten milk replacer — cow's milk is not an adequate substitute for queen's milk.
Sources
- Feeding Your Cat — Cornell Feline Health Center
- People Foods to Avoid Feeding Your Pets — ASPCA Animal Poison Control
This page is informational and is not veterinary advice. If your pet has eaten something risky, contact your vet or an animal poison control line right away.