Kittens have delicate digestive systems and find dry food difficult to digest. Therefore, it's best to feed them liquid foods such as wet food or formula. Cow's milk is obviously the most readily available milk source in our daily lives. However, there's a long-held belief that kittens shouldn't be fed cow's milk, but can be given goat's milk instead. Is this true? Is goat's milk really suitable for kittens? 
So why shouldn't you feed milk to kittens? Why do some kittens get diarrhea after being fed milk? This is because kittens may have a "lactose intolerance" reaction to the lactose in milk. Lactose is a disaccharide with the molecular formula C12H22O11. In nature, it only exists in the milk of mammals, hence its name. In mammals, especially young mammals during lactation, the intestines can secrete lactase, which breaks down lactose into glucose and galactose, two monosaccharides, which are then absorbed and digested.
However, if lactase secretion is insufficient or lactose intake is excessive, undigested lactose enters the large intestine directly, stimulating increased intestinal peristalsis and causing symptoms such as abdominal rumbling and diarrhea. This is known as "lactose intolerance." Lactose intolerance is common in mammals, and some humans also experience it. However, unlike adults, diarrhea caused by lactose intolerance can be fatal to kittens because it is often accompanied by severe dehydration. If vulnerable kittens do not receive timely treatment, they will die. Cow's milk has a relatively high lactose content; therefore, for safety reasons, it is not recommended to feed kittens cow's milk or cow's milk powder.
So, since cow's milk isn't suitable for kittens, can goat's milk be used instead? This is also incorrect. In fact, goat's milk doesn't prevent lactose intolerance as some advertisements claim, because it contains lactose in a similar proportion to cow's milk. Therefore, feeding kittens goat's milk or goat's milk powder also carries the risk of causing lactose intolerance. However, it's safe for lactose-tolerant kittens to drink it.
Of course, kittens need milk to grow and develop. Milk contains essential nutrients for their growth. But what if you can't find a wet nurse to provide milk for your kittens, and you can't determine if your cat is lactose tolerant?
At this stage, owners can choose lactose-free formula specifically formulated for kittens, which can be found in larger pet stores and online retailers. Lactose-free formula is made from lactose-free cow's or goat's milk, making it suitable for kittens with lactose intolerance. If the kitten also has fat intolerance, a low-fat lactose-free formula should be used. The fiber content in some lactose-free formulas may not be suitable for all kittens, as kittens' constitutions vary greatly. For kittens with sensitive constitutions, even slight differences in composition can cause gastrointestinal upset. However, for kittens with good constitutions who are not very sensitive to the fiber in lactose-free formula, it is safe to give them lactose-free formula.
