One of the major allergens in cows milk is the beta-beta-lactoglobulin (B-lg). B-Lactoglobulin is a globular protein that is present in the milk of many mammalian species including ruminants, such as cows and sheep, and some non-ruminants, such as pigs and horses. ?-Lactoglobulin is the major whey protein in milk.Order a beta-lactoglobulin allergy IgE blood test to detect an allergy to beta-lactoglobulin. This test measures the amount of allergen-specific antibodies in a blood sample. There are several proteins in cows milk that can cause allergies.