Species of Origin: Purified from Bovine milk. IgG antibodies are involved in predominantly the secondary immune response. The presence of specific IgG, in general, corresponds to maturation of the antibody response. IgG is the only isotype that can pass through placenta, thereby providing protection to the fetus in utero. Along with IgA secreted in the breast milk, residual IgG absorbed through the placenta provides the neonate with humoral immunity before its own immune system develops.Colostrum contains a high percentage of IgG, especially bovine colostrum.