Buddhism doesn't prohibit drinking milk or anything like that. But for Buddhist monks, all beings are equal, so things obtained from animals, such as milk, can be eaten without eating.

Taboos in Buddhist diet. Buddhism stipulates that there are many taboos in family diet, among which vegetarianism is the most basic and important one. The concept of vegetarianism includes not eating "meat" and "fish". "Meat" refers to vegetables with fishy smell and peculiar smell, such as garlic, green onions and leeks. The so-called "fishy smell" refers to meat, that is, the meat of various animals, even eggs.