Acute phase proteins in the diagnosis of bovine subclinical mastitis

Background: The California mastitis test (CMT) and somatic cell count (SCC) are commonly used for diagnosis of subclinical mastitis in cattle. Acute phase proteins (APPs), as alternative biomarkers of mastitis, may increase in concentration in the absence of macroscopic changes in the milk, or may precede the onset of clinical signs. Objective: The aim of this study was to compare the accuracy of APPs measured in milk and in serum with bacterial culture for the diagnosis of bovine subclinical mastitis. Methods: One hundred and seventy‐five Holstein cows were randomly selected from 7 dairy farms. Quarter milk and serum samples were taken from all cows. Milk samples were analyzed using a CMT and SCC, and for haptoglobin (MHp) and amyloid A (MAA) concentrations, and were also submitted for bacterial culture. Serum samples obtained concurrently were analyzed for haptoglobin (SHp) and amyloid A (SAA). Two‐sample Wilcoxon (Mann–Whitney) test was used to compare SCC, MAA, MHp, SAA, and SHp concentrations between culture‐positive and culture‐negative animals. Receiver‐operating characteristic analysis was used to assess the performance of each test using bacterial culture as the reference method. Results: MAA concentration was the most accurate of the 5 tests, with a sensitivity of 90.6% and specificity of 98.3% at concentrations >16.4 mg/L. MAA and MHp had significantly larger areas under the curve than the respective serum proteins, SAA and SHp. Conclusions: The results suggest that measuring haptoglobin and amyloid A in milk is more accurate than serum analysis for the diagnosis of subclinical mastitis in Holstein cows.