The diagnostic value of determination of positive and negative acute phase proteins in milk from dairy cows with subclinical mastitis

Currently, somatic cell count (SCC) and bacterial culture are considered as the gold standard methods for the diagnosis of bovine subclinical mastitis. However, SCC has a low diagnostic accuracy. Therefore, for identification of infected animals, new biomarkers with high diagnostic accuracy are needed. Acute phase proteins (APPs) are proteins that are increased (positive APPs) or decreased (negative APPs) in response to inflammation. The objective of this study was to determine the diagnostic value of milk APPs for the diagnosis of subclinical mastitis in dairy cows. A total of 90 clinically healthy cows were randomly selected. Of these, 52 cows were considered subclinical mastitic based on a SCC higher than 130 × 1,000 cells/mL of milk and positive bacterial culture results of milk samples obtained from at least one of the quarters. Milk amyloid A (MAA) concentration was measured using a commercial ELISA kit and albumin, α-lactalbumin, β-lactoglobulin, and immunoglobulin (Ig) were measured in the whey samples by the use of cellulose acetate electrophoresis. Diagnostic sensitivity and specificity and cutoff points for each test were determined via receiver-operating characteristics analysis. Significant (P < 0.001) increases in the mean and median concentration of MAA, albumin, α-lactalbumin, and Ig were found in the milk samples collected from cows with subclinical mastitis. MAA was the most accurate test with a diagnostic sensitivity of 92.3% and specificity of 92.1% at cutoff point of >1.6 mg/L. The results of this study showed that determination of MAA can be used as a reliable method for the diagnosis of bovine subclinical mastitis.