Composition of Milks of Dairy Cattle. I. Protein, Lactose, and Fat Contents and Distribution of Protein Fraction

Abstract

Milks from commercial dairy herds in Southeastern Pennsylvania were analyzed for total protein, casein, whey protein, β-lactoglobulin, nonprotein nitrogen, and lactose contents. Data for fat contents and milk yields were from Dairy Herd Improvement Association records for the same lactation. Milk samples were from a single milking of healthy cows (151) in midlactation. Since the remainder of the milk was returned to the bulk milk of the farm, the data represent market milk composition. The data were grouped and analyzed by breed and β-Lactoglobulin phenotype; there were 18 to 33 cows per breed. In true protein percentage, the breeds ranked: Jersey 4.07 ± .49, Brown Swiss 3.84 ± .47, Guernsey 3.56 ± .53, Ayrshire 3.30 ± .52, Milking Shorthorn 3.17 ± .47, Holstein 3.07 ± .43. Breeds differed in all other components and in milk yield. Brown Swiss ranked highest in yield of protein. Only whey protein and β-lactoglobulin contents were influenced by the β-lactoglobulin genotype with β-lactoglobulin A > AB > B in whey protein content.