Evaluation of Two Culture-Based Rapid Tests Utilized by Veterinary Practices as a Tool for Selective Treatment of Clinical Mastitis

Antimicrobial resistance necessitates more judicious antimicrobial use, also in dairy production where mastitis remains the primary driver of antibiotic consumption. Selective treatment of non-severe clinical mastitis (STCM) requires rapid differentiation between Gram-positive and Gram-negative pathogens, as only Gram-positive infections generally benefit from antimicrobial therapy. Because conventional laboratory culture is too slow for STCM, rapid testing systems for pathogen detection in milk are used on-farm (performed and analyzed by farm personnel) or on-practice (performed and analyzed at the veterinary practice). This study evaluated the diagnostic performance of 2 culture-based rapid tests (MicroMast® and VetoRapid®) via an on-practice culture approach as part of a clinical trial, with standard laboratory bacteriology as the gold standard. The performance to distinguish (1) Gram-positive from Gram-negative bacteria and (2) further pathogen identification was assessed by determining sensitivity, specificity, positive predictive values, negative predictive values, accuracy and Cohen's kappa values. Both tests (VetoRapid® more than MicroMast®) reliably distinguished Gram-positive from Gram-negative pathogens, supporting their use in STCM decision-making. However, their ability to identify specific pathogens was limited, restricting their suitability for broader udder health management decisions.