I am referring to domestic cats. The answer to the question is this. All domestic cats beyond the age of weaning are lactose intolerant. Before a kitten is weaned beginning at four weeks of age to around 10 weeks their intestines produce lactase; the enzyme that digests lactose. This capacity declines from birth to weaning. Without the enzyme lactase, lactose is not digested. The undigested lactose travels to the large intestine where it is fermented by bacteria. This results in the production of gas, loose stools and possibly diarrhoea. Diarrhoea is linked to lactose intolerance.
One study indicated that adult domestic cats can ingest 6 g of lactose per day without problems whereas 10-16 g causes intermittent and continuous diarrhoea. Another study tells me that “after the first year of life in most cats, the enzyme [lactase] completely ceases to be produced”. In practice, an occasional bowl of milk, perhaps once per month is acceptable.
One study by Kozlova Mariia Nikolaevna found that when cats are fed on cow’s milk for at least six months, which can occur in some countries, “preliminary examination showed that all animals have skin manifestations of allergies of varying severity”. Not only that, blood tests indicated that the cats had increased levels of leucocytes in their blood which is symptomatic of a chronic inflammatory process.
They say that “the ability of an adult animal to digests lactose sugars is an exception”. If despite the presence of diarrhoea because of lactose intolerance a cat owner continues to feed their cat cow’s milk they will become dehydrated and the higher the percentage of milk fat the sooner the degenerative process starts. i.e. the worse it gets and the quicker health deteriorates.
The researcher also concluded that consistently feeding a cat cow’s milk can lead to other serious health problems such as:
- An elevated body temperature in the range 39-41°C (from 37.5-39°C which is the norm).
- Rapid breathing of 25-30 breaths per minute
- Acute gastroenteritis which is inflammation of the digestive tract
- Colitis which is inflammation of the colon
- IBD as a result of chronic inflammatory process in the intestines
- In severe cases it can lead to hepatic lipidosis resulting in jaundice, conjunctiva of the eyes, dark urine, heart rhythm disturbance and the smell of acetone in exhaled air.
Once a lactose free diet is provided cats recover by the third week and by the sixth week they are back to normal. The conclusion is that there is a prolonged degenerative process leading to gastrointestinal tract disease and associated health problems if a cat owner feeds their cat consistently and persistently with cow’s milk over a long period of time.
PS: Many humans are also lactose intolerant and cow’s milk can cause bloating and these people. They should come off cow’s milk as soon as possible and use an alternative such as oat milk which will dramatically reduce bloating.
The studies: Clinical and Morphological Manifestations of Disorders of the Gastrointestinal Tract of Cats with Regular Consumption of Lactose Authored by Kozlova Mariia Nikolaevna and Milk for Cats authored by Anton Beynen.
Below are some more articles on diet.