While milk is not necessary to a dog's or cat's diet, it can be a treat if given from time to time. However, some pets cannot tolerate milk because they do not produce an enzyme called lactase. Lactase helps with the digestion of lactose, which is found in milk. After weaning, the level of lactase activity falls to about 10 per cent of its peak activity. In some animals, diarrhea will occur if more lactose (i.e. milk) is consumed than the pet can digest. This is called "lactose intolerance".
A further contributing factor is the fact that cow and goat milk contains 4.5% to 5% lactose, compared to 3.1% in dog's milk and 4.2% in cat's milk. The high level of lactose in cow's milk can overpower a dog or cat's ability to digest it. This is why many pups and kittens often get diarrhea from drinking cow's milk. This does not mean that milk is unhealthy for dogs and cats. On the contrary, in pets that are able to tolerate it, milk can be an excellent source of protein and calcium.
Pets with milk intolerance can still consume dairy products under certain circumstances. For example, dairy products such as cheese (including cottage cheese) and unpasteurized yogurt usually have the lactose removed or have it partially broken down through bacterial action. As a result, these products are often well tolerated by cats and dogs that would otherwise get diarrhea after drinking milk.
It should be stated that neither boiling milk nor the use of skim milk affects an animal's ability to tolerate milk, since the lactose content remains unchanged in either case. The same applies to pasteurized yogurt and cultured milk (e.g. buttermilk), neither of which is well tolerated by lactase-deficient pets.
Lactose intolerance, a fairly common digestive disorder in companion animals, is caused by an inability to digest lactose (a sugar found in milk), because the animal lacks the enzyme "lactase" in the small intestine. The clinical consequences of this disorder are intestinal discomfort and diarrhea. Dog and cat owners should be aware of these clinical signs so they can remove dairy products from their pet's diet if they suspect that lactose intolerance might be a problem.
Symptoms of Lactose Intolerance
The most common outward signs of lactose intolerance in dogs are abdominal pain, bloating, nausea, vomiting and diarrhea – fairly typical indications of gastrointestinal distress. This is not surprising, because the animal's gastrointestinal system is missing a key enzyme necessary to digest the sugars in milk. Sometimes, a dog will drink excess amounts of water when suffering from lactose intolerance, since the diarrhea and vomiting associated with the condition can cause dehydration and consequent thirst.
Lactose intolerance is an adverse reaction to milk and milk products, but it is not really an allergic reaction. Food allergies are adverse reactions to food that involve some inappropriate response by the animal's immune system. Food intolerance is an abnormal physiologic response to a food or a food additive that does not involve the immune system. Since the clinical signs of food intolerance can mimic those more commonly associated with food allergies, the two conditions are often confused. For instance, if a dog or cat licks its paws or rubs its face on the floor, its skin can become irritated and itchy. This could be the result of lactose intolerance if dairy products are a staple of the pet's diet, or it could be caused by an immunologic food allergy.
Different dairy products can affect different dogs in different ways. Cheese, for example, can cause constipation in some animals with lactose intolerance. This can cause the dog or cat to strain while trying to defecate, producing only small, hard, dry feces. Many owners supplement their pets' diets with yogurt or cottage cheese without and adverse consequences. Even puppies and kittens who have well-tolerated their mothers' milk can develop lactose intolerance – especially to cows' milk, which has higher lactose levels than does the milk from a bitch (female dog) or a queen (female cat). Lactose intolerance can cause diarrhea and an associated urgency in your dog to get to an appropriate area to relieve itself. The best rule of thumb for a dog or cat owner is to limit or simply eliminate dairy products from their pet's diet if lactose intolerance is suspected.