The main culprit is milk’s lactose, which many cats have trouble digesting.
The result: diarrhea or stomach upset. Not
Do cats and dairy ever get along? Can cats drink milk? Here is what cat
nutritionists and veterinarians told WebMD.
Cats and Dairy Fact 1: Lactose Intolerance Is the Norm
Just like people, cats can be lactose intolerant. And although we tend to
think that’s a problem, it’s actually completely normal, says Linda P. Case,
MS, adjunct assistant professor at the University of Illinois College of
Veterinary Medicine and author of The Cat: Its Behavior, Nutrition, and
“The only time animals are exposed to lactose is when they’re babies -- in
their mother’s milk," Case says.
To digest lactose, a milk sugar, the human and feline digestive systems must
contain the enzyme lactase. We have plenty of this enzyme in our systems at
birth, and it helps us thrive on our mother’s milk.
But as we grow up, it’s normal for people and cats to begin producing less
lactase. Less lactase means less ability to digest lactose. The result may
eventually be lactose intolerance.
When a lactose-intolerant cat drinks milk, the undigested lactose passes
through the intestinal tract, drawing water with it, according to
the Cornell University College of Veterinary Medicine's web site. Bacteria
in the colon also ferment the undigested sugars, producing volatile fatty
All that activity might lead to an upset tummy and induce vomiting. But the most
common symptom of lactose intolerance in cats is diarrhea, usually within eight
to 12 hours, says Susan G. Wynn, DVM, CVA, CVCH, an animal nutritionist in
Atlanta and co-author of the Manual of Natural Veterinary Medicine.