Can Cats Drink Milk?
Quick answer
Most adult cats should not drink milk.
The full answer
Like many adult mammals, cats lose most of the lactase enzyme after weaning, so the lactose in cow's milk is poorly digested and commonly causes diarrhoea, vomiting, gas and stomach pain.
Cats do not need milk at all once they are weaned. Water and a complete cat food supply everything they require, and dairy mainly adds calories that most indoor cats do not need.
Why lactose is the problem
Lactase is the enzyme that breaks lactose, the sugar in milk, into simpler sugars that can be absorbed. Kittens produce plenty of it because milk is their only food. After weaning, production falls, and in most adult cats the remaining amount cannot cope with a saucer of milk.
Undigested lactose draws water into the gut and is fermented by bacteria, which is why the result is loose stool, gas and cramping rather than anything subtle. Goat's milk is not a solution: it contains lactose too, and its fat and protein profile is not designed for cats.
What milk does and does not provide
Milk is not a source of anything a cat cannot get from a balanced diet. Adult cats have no requirement for dairy, and a complete cat food already supplies the calcium, protein and fat they need in the right proportions.
The practical downsides are calories and digestive upset. A small saucer of whole milk can add a meaningful share of an indoor cat's daily energy needs, and repeated bouts of diarrhoea are unpleasant for the cat and unhelpful for litter tray hygiene.
Kittens are a different case
Nursing kittens produce lactase and drink their mother's milk, which is exactly what their digestive system is built for. If a kitten must be hand-fed, use a commercial kitten milk replacer, never cow's milk or goat's milk.
Cow's and goat's milk do not match a kitten's nutritional needs, and in very young animals the resulting diarrhoea can quickly lead to dehydration and weight loss. Feeding frequency and quantities for orphaned kittens should follow the milk replacer's instructions and a veterinarian's advice.
If you still want to offer dairy as a treat
If your cat enjoys it and tolerates it, an occasional lactose-free product made specifically for cats is the safer choice. A teaspoon of plain, unsweetened yogurt is another common option. Keep the amount small and treat it as a snack, not a meal.
Introduce any dairy alone, on a day when nothing else has changed, so you can tell whether it caused a reaction. Cats that have never had dairy may also simply refuse it, and that is fine: there is no nutritional reason to persevere.
Signs of lactose intolerance
The usual signs appear within about eight to twelve hours: loose or watery stool, wind, gurgling stomach, vomiting and discomfort. In most healthy adults these settle within a day once the dairy stops.
Offer fresh water, keep meals plain and light, and contact your vet if the diarrhoea lasts more than a day or two, contains blood, or comes with lethargy, repeated vomiting or refusal to eat. Very young, very old and unwell cats dehydrate faster than healthy adults, so seek advice sooner for them.
Better ways to add water and treats
Cats evolved as desert hunters and often drink less than they should, but milk is not the answer. Wet food is the simplest way to raise water intake, and many cats drink more from a circulating fountain than from a still bowl.
Locate water bowls away from the food and litter tray, offer several around the house, and refresh them daily. For treats, small pieces of plain cooked meat or commercial cat treats give the same pleasure without the lactose.