Progressive changes in individual milk protein concentrations associated with high somatic cell counts

Abstract

Summary: Progressive changes in the concentrations of milk protein components were followed after infusions ofStreptococcus agalactiaeor bacterial endotoxin into different quarters of individual cows. Both types of infusion produced similar increases in somatic cell count and resulted in similar changes in milk proteins, although the effects of the endotoxin infusion lasted for a shorter length of time.The treatments had little effect on α-lactalbumin and β-lactoglobin concentrations, but serum albumin and immunoglobulin (Ig) concentrations increased markedly. The greatest effect on serum albumin was after the endotoxin infusion and on Ig after theStr. agalactiaeinfusion. Changes in the individual globulins indicated that passive transfer of blood proteins to milk could not account for the observed increases in IgM and IgA.α_s1-Casein and β-casein concentrations were reduced and inversely related to somatic cell count during the immediate post-infusion period, and this was accompanied by an increase in para-κ-casein. Para-κ-casein was not detected in pre-infusion or post-recovery milk samples. The decrease in β-casein was greater than that of α_s1-casein. Casein concentrations returned to pre-infusion levels 2 d and 5 d after the endotoxin andStr. agalactiaeinfusions respectively.The possibility that proteolytic enzymes are partly responsible for the changes in casein concentration is discussed.