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Why do cows give milk? People have used milk for food from ancient times, and have developed certain animals to supply large amounts of milk. We depend on cows to supply most of our milk, but in Spain, for example, the sheep is one of the chief milk-producing animals. Many desert tribes depend on the camel for milk, and in Egypt, they use water buffaloes. In Peru, the llama is a milk-producing animal. People in many countries use goat's milk. Milk is the fluid secreted by the mammary glands of the animal as food for their young in the period immediately after birth. It takes the place of the blood which supplied the young with nutrition before it was born. In fact, it is exactly like blood, only without the red blood cells and the blood pigment. The composition of milk varies quite a bit, depending on the species of the animal which produces it. But milk always contains fat, protein, carbohydrate, and minerals. Goat's milk, for instance, contains twice as much fat as cow's milk, and the milk of reindeer contains five times as much fat as cow's milk! The milk of every animal also contains various salts according to the needs of its young. The more rapid the growth of the newborn, the more salts in the mother's milk. A cow doubles its original weight at birth in 47 days, but a human being does it in 180 days. That's why cow's milk is too rich in proteins and salts and must be diluted for feeding newborn children. The milk produced by cows varies depending on many factors. One, of course, is the breed of cow and the constitution of the individual cow. Another is the time between milkings. The last milk to be drawn at each milking is richer in fat than the rest. So, if a cow has not been completely milked, it will probably have fatter milk next time. Since green food is the main source of vitamins for the cow, summer milk is usually richer than winter milk, when the cow can't walk about in the pasture. About 110 grams of food solids are contained in each litre of milk. The most important solids are the butterfat, the casein, the milk sugar, and the minerals. For Details
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