Milk proteins in bovine mastitis: biomarkers of disease and biological function

Mastitis is the most common and expensive health problem of dairy cattle and is mainly caused by intra mammary bacterial infection. Its control and management are the main reasons for antimicrobial usage (AMU) in dairy cattle with the potential for the development of antimicrobial resistance (AMR). Mastitis can occur as a subclinical or clinical form and in the latter the classical symptoms can be observed being swelling, tenderness, raised temperature and redness of the affected udder quarter along with clots in the milk. Mastitis is routinely diagnosed by assessment of the somatic cell count (SCC) in milk but there are questions on the sensitivity and specificity of this methods for accurate diagnosis. We have identified by immunoassay that acute phase proteins such as haptoglobin (HP) and serum amyloid A (SAA) when present in milk are potentially sensitive biomarkers of mastitis, but clinical validation is lacking. We have also determined by tandem mass tag (TMT) proteomics that further biomarkers of mastitis could be valuable in mastitis detection and monitoring. Advanced proteomics such as data-independent acquisition (DIA) and SWATH analysis and multiple reaction monitoring (MRM) will extend the sensitivity of proteomic analysis of milk cows comparing healthy milk with milk from animals with subclinical mastitis which is key to improving cow health by allowing early detection and intervention.