Colostrum (known colloquially as beestings, bisnings or first milk) is the first form of milk produced by the mammary glands of mammals (including many humans) immediately following delivery of the newborn. Most species will generate colostrum just prior to giving birth. Colostrum contains antibodies to protect the newborn against disease. In general, protein concentration in colostrum is substantially higher than in milk. Fat concentration is substantially higher in colostrum than in milk in some species, e.g. sheep and horses, but lower in colostrum than in milk in some other species, e.g. camels and humans. In swine, fat concentration of milk at 48 to 72 hours after parturition may be higher than in colostrum or in late-lactation milk. Fat concentration in bovine colostrum is extremely variable.Newborns have very immature and 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 is known to contain immune cells (as lymphocytes) and many antibodies such as IgA, IgG, and IgM. These are some of the components of the adaptive immune system. In preterm infants some IgA may be absorbed through the intestinal epithelium and enter the blood stream though there is very little uptake in full term babies. This is due to the early "closure" of the intestinal epithelium to large molecule uptake in humans unlike the case in cattle which continue to uptake immunoglobulin from milk shortly after birth. Other immune components of colostrum include the major components of the innate immune system, such as lactoferrin, lysozyme, lactoperoxidase, complement, and proline-rich polypeptides (PRP). A number of cytokines (small messenger peptides that control the functioning of the immune system) are found in colostrum as well, including interleukins, tumor necrosis factor, chemokines, and others. Colostrum also contains a number of growth factors, such as insulin-like growth factors I (IGF-1), and II, transforming growth factors alpha, beta 1 and beta 2, fibroblast growth factors, epidermal growth factor, granulocyte-macrophage-stimulating growth factor, platelet-derived growth factor, vascular endothelial growth factor, and colony-stimulating factor-1.Notably in humans a lack of colostrum production is linked to a mutation in the ABCC11 gene that occurs in most people of East Asian descent. This gene is also one the determining factors in wet or dry type earwax, as the mammary glands are a form of apocrine gland.