Evaluation of an on-farm culture system for the detection of subclinical mastitis pathogens in dairy cattle

The purpose of this observational study was to compare the performance a novel on-farm culture (OFC) test with reference method (RM) in identifying pathogens, and particular Staphylococcus aureus, associated subclinical mastitis (SCM) dairy cattle. OFC (Mastatest HiSCC; Mastaplex Limited) for SCM uses cartridge 2 × 12 wells allowing 1 sample be analyzed duplicate (24 wells) or samples simultaneously, each wells. Results milk analyses are reported hierarchically (Staph. aureus → coagulase-negative staphylococci (CNS) other gram positive coliform/gram negative no bacteria present) emailed within 24 h. Milk (617 quarter level from 158 cows 70 cow level) were collected 288 [individual somatic cell count (ICSCC) ≥150,000 cells/mL] on 9 purposefully selected farms known have high prevalence clinical Staph. Southland New Zealand. Quarter individually samples) after animal-level pooling, providing 228 (158 + 70) cow-level samples. Samples by (in duplicate) RM (culture agar medium latex based recommendation National Mastitis Council) identifications confirmed MALDI-TOF mass spectrometry. Sensitivity (Se), specificity (Sp), predictive value (PPV), (NPV) detection all ~90% tight 95% confidence limits, Cohen's kappa (κ) agreement between 0.81. Kappa duplicates 0.93. About 35% had only one infected these animals could still identified when pooled analyzed. Although herds used does not affect Se Sp values, it elevate PPV (and decrease NPV) therefore use extrapolate population lower is appropriate. For CNS, Sp, PPV, NPV >0.8, κ ≥0.6, >0.7. 0.83. A result “no detected” 13% 93% RM. We conclude that provides reliable detecting even if infected; absence milk, reliably CNS milk; <10 cfu/10 µL their milk. Compared RM, rapid results returned h loading cartridge.