Colostrum: back to basics with immunoglobulins.

Colostrum is a vital component to the raising of nearly all mammalian newborns, especially those reared domestically for agricultural purposes. Colostrum contains multiple immunoglobulins (Ig; IgA, IgM, IgG, etc.), with the most abundant Ig in colostrum generally being IgG. The various Ig molecules serve different purposes within the neonate. Immunoglobulin M is primarily made during the primary immune response and is usually found in higher quantities than IgA, which congregates on epithelial surfaces and is found in high content in saliva (Tizard, 2013). Immunoglobulin G, a large globular protein with a molecular weight of roughly 150 kDa, is the most commonly discussed Ig in calf-raising and is measured in calf serum around 24-h post-colostrum feeding to evaluate passive transfer of immunity (PTI). Passive transfer of immunity rates on a given operation are a critical benchmark to determine how well colostrum is managed. Producers, veterinarians, and consultants must understand how PTI is achieved to ensure this critical objective is achieved consistently by calves on farm. The following review is intended to help summarize the understanding of how PTI is achieved, and what factors in maternal colostrum (MC) influence PTI.