🐾 Other mammals

Other mammals are mammals that nurse their young with milk but are not a source of milk for people. All mammals produce milk — from tiny shrews to the blue whale — but humans milk only a few dozen species. The rest feed their young with milk that is out of people’s reach or of no interest to them, yet it tells a great deal about how each species lives.

The composition of milk is tuned to the young animal’s way of life. In seals, which nurse their pups for a few days or weeks on the ice, milk can be 25–60% fat. In baleen whales it reaches 40–50%, and a blue whale calf gains about 90 kg a day. Polar bears, which nurse their cubs in a den, have milk with about 27–33% fat. In elephants lactation lasts for years, and the fat content of the milk gradually rises. Pigs, by contrast, let down milk for only 20 seconds per feed, which makes them impossible to milk.

Such data are not just a matter of curiosity: they are used to formulate milk replacers for orphaned young in zoos and rehabilitation centres. Comparing the milk of different species helps show how evolution has adapted the same “product” to very different conditions — from the tropics to the Arctic and the ocean.