The newborn calf is practically devoid of vitamin A, and since it provides a degree of protection against various diseases every calf should be fed colostrum. At parturition milk production commences at a relatively high rate, and the amount secreted continues to increase for about 3 to 6 weeks. Higher-producing cows usually take longer than low producing cows to achieve peak production. After the peak is attained, milk production gradually declines. The rate of decline is referred to as persistency .
Nonpregnant cows can continue to secrete milk indefinitely, but at a reduced rate.
Fat percentage in milk decreases slightly during the early lactation and then increases as total production decreases with advancing lactation. Milk protein content gradually increases with advancing lactation. Lactose and mineral concentrations increase slightly during advancing lactation. Most of the increase in SNF components of milk is associated with advancing stages of concurrent pregnancy rather than stage of lactation. The reason for this distribution of the fat globules is not known.