Composition of Proteins in Milk with Varying Leucocyte Contents

Abstract

A total of 237 quarter samples from 34 Holstein and 26 Guernsey cows were collected within 7 days. Leucocyte counts by the Wisconsin Mastitis Test and pH were determined within a few hours after collection. Skim milk was analyzed for total proteins, caseins, and whey proteins as well as for the electrophoretic fractions of αs1-, β-, and κ-casein, β-lactoglobulin, serum albumin, α-lactalbumin, and immunoglobulins. Except for total protein contents, all other concentrations changed with increasing leucocyte counts in each breed. Milk samples with higher leucocyte counts had less total casein, lower ratios of casein to total protein, and higher contents of total whey proteins than samples with lower leucocyte counts. They also showed decreased amounts of αs1-casein, β-casein, β-lactoglobulin, and α-lactalbumin while amounts of immunoglobulins, serum albumin, κ-casein, other unidentified proteins, and pH increased. Leucocyte counts were higher in advanced stages of lactation and with higher age of cows. No relationships between leucocyte counts and genetic polymorphisms of proteins were found. Bacteriological tests showed less growth in samples with lower leucocyte counts.