Human and bovine colostrums are thick, sticky and yellowish. In humans, it has high concentrations of nutrients and antibodies, but it is small in quantity.

Colostrum is high in carbohydrates, high in protein, high in antibodies, and low in fat (as human newborns may find fat difficult to digest). Newborns have very small digestive systems, and colostrum delivers its nutrients in a very concentrated low-volume form. It has a mild laxative effect, encouraging the passing of the baby's first stool, which is called meconium. This clears excess bilirubin, a waste product of dead red blood cells which is produced in large quantities at birth due to blood volume reduction, from the infant's body and helps prevent jaundice.

Colostrum contains large numbers of antibodies called "secretory immunoglobulin" (IgA) that help protect the mucous membranes in the throat, lungs, and intestines of the infant. Leukocytes are also present in large numbers; these begin protecting the infant from harmful viruses and bacteria. Ingesting colostrum establishes beneficial bacteria in the digestive tract.

Premature babies tend to fare better on human colostrum than commercial infant formulas. Human milk contains special components, called growth modulators, that help the premature baby's digestive system adjust to oral feedings. Research indicates that premature babies fed formula tend to vomit more and continue tube feeding longer than those fed human colostrum and breast milk.