Early pathogenesis and inflammatory response in experimental bovine mastitis due to Streptococcus uberis

A generally similar clinical response was observed in six lactating Holstein-Friesian cows after intramammary inoculation with approximately 10(7) colony-forming units of Streptococcus uberis. Increased concentrations of serum amyloid A (SAA) were measured in both milk and serum taken 6 and 11h after inoculation, respectively. In contrast, increased concentrations of haptoglobin were detected after 10h of infection, in milk only. In the blood, tumour necrosis factor-alpha (TFN-alpha) was detected (0.503 ng/ml) in only one animal, at the time of euthanasia (10h after infection). Interferon-gamma (IFN-gamma), like haptoglobin, was not detected in blood. Parallel to the development of inflammation and influx of inflammatory cells into the udder tissue, a marked decrease in the number of monocytes and neutrophils in blood was observed. Bacteria were found both intracellularly (macrophages and neutrophils) and within the lumen of ducts and alveoli. Lesions developed progressively in an ascending manner and became widespread throughout the mammary gland in less than 8h. The parallel development of inflammation and increased concentrations of SAA and haptoglobin in milk points to these acute phase proteins as potential diagnostic markers for the early detection of S. uberis -associated mastitis.