Postpartum Changes in Milk Serum Protein Fractions

Polyaerylamide gel disc electrophoresis was used to study changes in the relative concentration of the fi-lactoglobulin, alaetalbumin, blood serum albumin, and immune globulin in milk serum during the first 21 days post-partum. All four protein fractions were found to be concentrated in cotostrum serum at parturition, with immune globulin being a major fraction. A graphic analysis of the change in the total protein of the four fractions studied indicates that this change behaves as a biphasic process. The first phase, a simple dilution effect, lasts approximately 60 hr. In ten days a fairly stable relationship is established between the relative concentration of the four protein fractions of milk serum, with fi-lactoglobulin being the major fraction.