Biochemical Parameters in Milk Triggered by Bacterial Pathogens Causing Subclinical Mastitis

Subclinical mastitis is characterized by inflammation in the udder without any signs of clinical illness. Udder inflammation is mainly associated with major alterations in biochemical milk components, which may be identified as indicators for pathogenic infections. To identify key biochemical changes in milk relevant to early detection of subclinical mastitis, milk samples were collected from 10 healthy cows and 50 cows diagnosed with subclinical mastitis based on the California Mastitis Test, followed by analysis of bacterial contents and biochemical components. The bacteriological analysis revealed that S. aureus was the main pathogen associated with subclinical cases (32%) either as a single infection or mixed with E. coli (4%) or Klebsiella spp,. (8%). Single bacterial infections by E. coli, Klebsiella spp., and Enterobacter spp. were detected in 7%, 7% and 3% of the subclinical mastitis cases, respectively. Biochemical composition analysis of bacteriologically positive milk samples versus healthy samples showed a significant decrease in important electrolytes (Ca, P, K, Mg) and total proteins, in addition to a significant increase in blood electrolytes (Na & Cl), and C-reactive proteins (CRP). The result showed no significant difference in all parameters except for CRP between single and mixed bacterial infections. Albumin concentrations showed no significant changes in all tested milk samples, while vitamin E & A concentrations showed variation among the tested milk samples. In conclusion, CRP as well as total protein, blood and important electrolytes, have potential as biomarkers for subclinical mastitis, suggesting that they could be integrated as practical tests to monitor dairy herd health and early detection of subclinical mastitis.