Ultra Low IgG Fetal Bovine Serumlow IgG fetal bovine serum is selected from lots with naturally low amounts of IgG. IgG is the major immunoglobulin found in normal animal serum, accounting for 70 75% of the total pool. It is a natural serum component involved in immune function and the only class of immunoglobulins able to cross the placenta. Natural bovine serum IgG can interfere with cell culture studies in which the cells may be producing a specific IgG molecule of interest.