Milk a drink that has been used by humans ever since we first started domesticating animals, the first traces of people using cow milk for food has been found in the Middle East. Grass is otherwise useless to humans but to goats, sheep and cows it is the key to survive, grass is also easily stockpiled so by domesticating these animals, humans could turn grass into sustenance. The main function of milk is, of course, not to feed humans but to serve as a nutritional alternative to several different mammals, including humans, before they are old enough to digest other types of food.
Milk contains a lot of different components depending on species, but all milk is high in saturated fat, protein, calcium, and vitamin C, the milk that is fed to the mammal early on in life is called colostrum and carries a lot of antibodies from the mother to the baby. The top three consumers of milk per capita per year in the world is Finland (183.9L), Sweden (145.5L), and Ireland (129.8L).
In addition to cow milk, camels, donkeys, goats, horses, reindeer, sheep, water buffalo, and yak milk also exists, in Russia and Sweden, moose dairy products exist as well. Around 250 ml of cow milk contains around 285 mg of calcium which represents 22% to 29% of the daily recommended intake for a grown human, recent studies also show that low-fat milk can reduce the risk of arterial hypertension, coronary heart disease, colorectal cancer, and obesity. People who are overweight can reduce the risk of insulin and type-2 diabetes.
Depending on country, milk comes in a large variety of packaging, in China it is popular to drink milk from small plastic bags with a straw, in Sweden milk is commonly sold in .3L, 1.5L, and 2L cartons, and in Uruguay milk is mainly sold in 1 litre bags which are then places in jugs with the corner cut off before the milk can be served.