Using biomarkers to detect intramammary infections in dairy cows at dry-off.

Prevention and treatment of intramammary infections (IMI) associated with subclinical mastitis (SCM) are among the leading reasons for antimicrobial usage (AMU) in dairy cows, especially at dry-off. By adopting a selective dry cow therapy ((S)DCT), only cows or quarters with a demonstrable risk of IMI would be treated and AMU would be decreased. Several tools have been proposed to identify cows for SDCT, including algorithms based on clinical mastitis and somatic cell count (SCC). The potential of milk proteins as biomarkers for IMI at dry-off has not been fully evaluated. In this study, biomarkers in 185 milk samples collected aseptically at drying off were quantified and their value in detecting IMI was evaluated (individually and in combination) in comparison to SCC and California Mastitis test using a case-control design with culture-based detection of IMI as gold standard comparator. Biomarkers quantified were lactoferrin, α-lactalbumin, haptoglobin, mammary amyloid A, C-reactive protein and cathelicidin. Of the six biomarkers examined, three had accuracies greater than 61% based on univariate biomarker trees (62%, 65% and 65% for haptoglobin, cathelicidin and milk amyloid A, respectively). A two-biomarker decision tree combining cathelicidin and milk amyloid A improved overall accuracy to 70% (sensitivity 72%, specificity 67%), comparable in performance to SCC, maintaining an acceptable level of sensitivity, but with greater specificity - an attribute desirable for SDCT. This performance highlights its potential use as a practical tool to reduce unnecessary antimicrobial treatments at dry-off, supporting selective dry cow therapy without compromising detection of infected quarters.