The best studied substances in bovine colostrum are the immunoglobulins. They are absorbed in the small intestine of the neonate by pinocytosis. The Fc-receptor is not highly involved in this process in calves compared to other species. However, this receptor plays a crucial role in the transport of immunoglobulins from the circulation of the dam to the udder and, therefore, into the colostrum. During colostrogenesis, which starts up to 8 weeks prior to parturition, up to 500 g of immunoglobulins are transferred daily by this process. In addition, other components of the bovine colostrum have biological activity. Colostrum-derived growth factors, including IGF-1, EGF and TGF, influence the differentiation of the epithelial cells of the gastrointestinal tract and, therefore, its development. In the udder of the dam, they are involved in various mechanisms of adaption throughout the lactation period. Colostral leucocytes are also transported from the colostrum into the circulation of the offspring, this by a process termed cellular migration. These cells have a specific immunological memory and support the calf in the development of an immune response against specific pathogens the dam was exposed to earlier. Colostral enzymes can be used as an indirect parameter to control for an adequate colostrum supply of the calf (e.g. γ-glutamyltransferase) or have an unspecific antimicrobial potential capacity (e.g. lactate peroxidase, lactoferrin, lysozymes). Vitamins, fats, proteins and mass and trace elements in the colostrum are essential nutrients for the bovine neonate because of the great change in the requirements for the neonatal organism from preto postnatal life. The impact of hormones and other components of the colostrum is still mostly unclear. The composition of the colostrum in the individual cow is influenced by numerous factors, including the number of calvings, the amount of colostrum formed and breed of the dam.
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