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Intestinal Protective Factors in Colostrum and Milk


Piglets suckling a sow.

Several factors found in milk may function in the neonate's digestive tract to minimize the potential for enteric disease. These include:

Immunoglobulins - Even after closure the immunoglobulins in milk may protect the intestinal lumen. Immunoglobulins are relatively resistant to digestion. IgA is of particular concern in the human infant because it is the major immunoglobulin in human milk.

Lactoferrin - The iron-binding capacity of lactoferrin gives it bacteriostatic and bactericidal properties. Lactoferrin is high in human milk, low in cow milk.

Lysozyme - May degrade the cell wall of some bacteria and allow them to be lysed. Lysozyme is high in human milk, but there is essentially none in cow milk. Lysozyme can act in concert with IgA, lactoperoxidase and ascorbate to lyse bacteria.

Lactoperoxidase - Uses hydrogen peroxide and halogens (I, Cl) to halogenate proteins and make them inactive. Also causes peroxidation of substances. The lactoperoxidase system also includes an interaction of the enzyme with thiocyanate. Lactoperoxidase activity is ~20 fold lower in human milk than cow milk, but the human infant also secretes considerable lactoperoxidase in the saliva.

Milk cells - Generally the leukocytes in normal milk (no mastitis) are macrophages. These cells probably retain some of their phagocytic abilities when ingested into the neonate. However, a role for these cells in the neonate has not been completely described.

Gut Flora - One of the best mechanisms for protecting against digestive tract infections is the establishment of the proper intestinal flora. In human milk there is a carbohydrate growth factor (called the Bifidus Factor, probably an oligosaccharide) which stimulates the growth of Lactobacillus bifidus. The high lactose concentration, low protein content, low bulk and low buffering capacity of human milk also encourages L. bifidus growth. The high lactose content means that lactose is still available for bacterial fermentation in the intestine, resulting in an acidic environment which reduces viability of many potentially pathogenic bacteria. Although similar factors to the Bifidus factor have not been identified in milk of other species, there may be other milk factors that contribute specifically to the establishment of the optimal microbial flora in the digestive tract.

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