Relationship of Milk Proteins in Blood with Somatic Cell Counts in Milk of Dairy Cows

Abstract

Intramammary leucocytosis was induced by injection of Escherichia coli endotoxin via the teat canal in three lactating Holstein cows. Concentrations of .alpha.-lactalbumin and casein in blood serum were measured, and somatic cell concentrations and yield and composition of milk were determined. Endotoxin injection elicited mean increases of 1000-fold in somatic cell concentration and 50% in protein concentration, whereas milk yield declined 5-fold and lactose concentration was halved. Concentrations of .alpha.-lactalbumin and casein in blood rose from 80 to 1909 and 0 to 1231 ng/ml, respectively. By 96 h postinjection, all variables were approximately equal to those preinjection. In a second study, concentration of .alpha.-lactalbumin was determined in blood of lactating cows in two herds (n = 332) and related to milk somatic cell count. Concentrations of .alpha.-lactalbumin in blood were correlated with somatic cell counts (r = .60). Mean concentrations of .alpha.-lactalbumin increased with increasing cell count even at low somatic cell concentrations (25 to 250 .times. 103). Concentrations of milk proteins in blood serum apparently reflect compentency of the blood-milk barrier and may therefore yield an indirect meausre of udder health.