Categories: diarrhea

Why does milk cause diarrhoea in cats?

It’s pretty well known across the cat world that cow’s milk causes diarrhoea in cats. Notwithstanding that there are thousands of photographs of domestic cats lapping up milk out of a saucer on the Internet. These are often old photographs from archives dating back many years. Cats do like milk because it contains a high level of fat but they don’t realise it’s not good for them. Fortunately, nowadays most cat owners realise it.

Kittens drink milk. Painting by Meta Plückebaum

I will explain in a little bit of detail why milk causes diarrhoea (a symptom) in cats. The first point to make, I think, is that it doesn’t cause diarrhoea in all adult cats and kittens. It occurs in some cats and some kittens because some cats lack adequate amounts of the enzyme lactase. This enzyme aids in the digestion of milk sugars. Milk sugars are present in all dairy products.

As a result there is unabsorbed sugar in the cat which is called lactose. This holds water in the small intestine. This results in increased motility. The word “motility” in this context means the stretching and contractions of the muscles of the gastro-intestinal tract (the gut). These muscles move the digestive food down the gut.

The increased motility is accompanied by a large volume of stool. These factors lead to diarrhoea.

It’s no good looking for substitutes designed for humans, either. For example, almond milk or soy milk are sweetened for the human palate. Sometimes they contain artificial sweeteners which are not good for cats. Some cats like ice cream. However, once again, this food is not very good for a cat’s health. It is very high in sugar content which is not good for a cat’s teeth.

It’s possible that some cats ingest milk with their human companion’s cereal which contains lots of sugar. Apparently, sugar can trigger hypertension in some cats. These sorts of “treats” should be given prudently.

P.S. If I treat my cat with milk (rarely) I use lactose free milk or commercially prepared cat milk which he does not like that much as it happens.

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Michael Broad

Hi, I'm a 71-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I have a girlfriend, Michelle. I love nature, cats and all animals. I am concerned about their welfare.

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  • If you absolutely must give your cat a milk product, real cream has less lactose than other milk products. It could be more digestible in small amounts. Of course the higher calorie count and high fat content need to be considered also. 🐾
    https://www.healthline.com/.../dairy-foods-low-in-lactose...

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