The milk secreted by cows in the first week after delivery is called colostrum. Colostrum is yellow and thick, rich in nutrition, slightly salty and peculiar, and solidifies when boiled. The content of various components in colostrum is very different from that in normal milk. The dry matter content is obviously high, such as protein as high as 17%.

The special function of colostrum:

The gastrointestinal mucosa of newborn calves is not well developed, and the resistance to bacteria is very weak. Colostrum is coated on the gastrointestinal wall, which can prevent bacteria from invading the blood and improve the disease resistance. Colostrum contains immune antibodies or immunoglobulin (γ-globulin) to make calves acquire acquired passive immune function and resist infectious diseases. Lysozyme in colostrum can kill many kinds of bacteria, such as Escherichia coli. Because antibodies can't penetrate the placenta, feeding colostrum is the only way for calves to obtain immunoglobulin.

High initial lactic acid can make gastric juice acidic and inhibit the reproduction of harmful bacteria. Promote the secretion of digestive juice and digestive enzymes by abomasum, and promote the establishment of gastrointestinal function. Colostrum contains more inorganic salts, among which magnesium salt is high, which has a laxative effect and promotes the elimination of meconium in the intestine. Rich in nutrients, the contents of vitamin A and vitamin C are about 10 times higher than those of normal milk, and the contents of vitamin days are about 3 times higher. Within 1-2 days after delivery, the chemical composition of cow colostrum is close to that of newborn calf's blood, and the albumin in it can directly enter the blood through the intestinal wall, rapidly increasing the plasma protein concentration of young animals.

There are many indispensable and alternative nutrients in colostrum of newborn calves. There are two important functions for calves to eat colostrum. First, colostrum contains a lot of antibodies or immunoglobulins that newborn calves do not have. By feeding colostrum, newborn calves can gain passive immunity and improve their resistance to diseases. Second, the nutritional value of colostrum is much higher than that of normal milk, in which the dry matter is 2-3 times higher than that of normal milk, and the protein, fat and minerals are all higher than that of normal milk, and it is particularly easy to be digested by cows. At the same time, colostrum contains high amounts of lactic acid, magnesium salt and calcium salt, which can not only inhibit the reproduction of harmful microorganisms in the intestine and prevent digestive system diseases, but also stimulate the secretion of digestive juice and bile, promote the digestion process and promote meconium production of veal steak. Therefore, newborn calves should be fed colostrum in the shortest time after birth.