The significance of some significant features of breast milk.

: The composition of milk shows reasonable species variation. Further, the composition in a given mother changes with the stage of lactation. It appears reasonable to assume that nature arranges the secretion of milk of a composition which is best suited for an infant. The colostrum, secreted during the first five days of lactation, has higher concentration of total protein, lactoferrin, and immunoglobulins but lower concentrations of fat and lactose. The milk secreted from day 6 through 15 is called transitional milk because its composition is intermediate between that of colostrum and mature milk which follows. Even in mature milk, small changes in composition go on throughout lactation. Further, if the infant is preterm, the composition of milk is different, and its appears to be more suitable for the premature infant. A large number of biochemical differences are now known between human milk and animal milk. Although the significance of several of these differences is not known, enough is known to explain why breast milk is better digested and more protective against infections. Besides, some constituents of breast milk might also have a role to play in growth and metabolism of the infant.