In chickens, immunoglobulin Y is the functional equivalent to Immunoglobulin G (IgG). Like IgG, it is composed of two light and two heavy chains. Structurally, these two types of immunoglobulin differ primarily in the heavy chains, which in IgY have a molecular mass of about 65,100 atomic mass units (amu), and are thus larger than in IgG. The light chains in IgY, with a molar mass of about 18,700 amu, are somewhat smaller than the light chains in IgG. The molar mass of IgY thus amounts to abo