Fractionized milk composition in dairy cows with subclinical mastitis

Mastitis is the inflammatory reaction of the udder to invading pathogens. One of the most apparent reactions is the increased influx of immunoreactive cells from blood into milk inducing a dramatic increase of milk somatic cell counts (SCC). We have investigated (i) the relationship between log SCC/ml in infected quarters being >6 (n = 8, group I) or varying between 5.4 and 6 (n = 8, group II) and concentration of dry matter (DM), fat, protein, lactose, insulin-like growth factor (IGF)-1, insulin, prolactin, tumor necrosis factor (TNF)-alpha, sodium, potassium, chloride, electrical conductivity and osmolarity as compared with the contralateral (healthy) quarter (log SCC/ml <5.2); and (ii) composition of fractionized milk [cisternal milk, quartiles of alveolar milk and residual milk (after i.v. injection of 10 u.i. oxytocin)] during machine milking of infected and healthy quarters. SCC were higher (P < 0.05) in infected than in healthy quarters. Concentrations of fat, sodium, chloride, and IGF-1 were higher (P < 0.05), while that of lactose was lower (P < 0.05) in infected than in healthy quarters (group I). Concentrations of fat and chloride in both groups, of DM (in group II), and electrical conductivity and sodium (in group I) increased from the cisternal to alveolar (100%) fractions in infected quarters, while fat and DM concentrations similarly increased in healthy quarters. In conclusion, several but not all milk traits changed in a different manner during the course of milking in infected and non-infected quarters.