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Can dogs and cats be lactose intolerance?

Question: Can dogs and cats be lactose intolerant?

Answer: Adverse reactions to certain foods are common in both dogs and cats. However, when we talk about possible reactions to foods, it is important to be clear about the difference between a food “allergy” versus a food “intolerance”. If there is an immunological basis to the adverse reaction, it is called a "dietary allergy or hypersensitivity". However, if there is no immunological basis for the reaction, the correct term to use is "dietary intolerance".

Can dogs and cats be lactose intolerance?

Lactose intolerance is a form of  dietary intolerance and does occur in dogs and cats. Since they can also get allergies to milk and dairy products, it is important to differentiate between these two conditions in order to treat them properly.

From a clinical perspective, pets with lactose intolerance usually exhibit gastrointestinal problems such as diarrhea and vomiting when consuming milk. By contrast, pets with milk allergies suffer primarily from itchy skin with or without a history of recurrent ear and skin infections.  Intestinal involvement such as occasional vomiting and/or loose stools only occurs in a small percentage of pets with milk allergies.

Pets with lactose intolerance lack the enzyme lactase, which hydrolyzes lactose,  a sugar found in milk and dairy products. Pets with a lactose intolerance can tolerate some dairy products such as cheeses in some situations. This is because, with dairy products like cheese, cottage cheese, and unpasteurized yogurt, the lactose has been extracted or partially broken down through bacterial action. 

In the case of boiled or skim milk, a pet may be intolerant because the lactose has not been modified in any way.  The same can be said about pasteurized yogurt and cultured milk (e.g. buttermilk), neither of which are tolerated by lactose intolerant dogs and cats. Pets that have lactose intolerance do not outgrow it and tend to have it for life.

The only way to determine whether a pet is lactose intolerant or allergic to dairy products is by eliminating milk and dairy products for a few weeks.   The elimination diet should result in a cessation of symptoms.  A re-introduction of milk should then result in diarrhea in the case of lactose intolerance and itchy skin in the case of milk allergies.

The fact that milk allergies and lactose intolerance exist does not mean that it is unhealthy to feed milk to dogs and cats.  On the contrary, if a pet is able to tolerate milk, it can be an excellent source of protein and calcium.