Preliminary validation of an on-farm culture system.

There is increasing adoption of on farm culture systems for selective treatment of clinical mastitis cases. They may also be useful for the diagnosis and selective treatment of subclinical intramammary infections in fresh cows. We present preliminary validation of an on-farm culture system (Minnesota Easy Culture System II). Farm personnel collected milk samples from clinical mastitis quarters, and from fresh cow quarters that tested positive using the Californian Mastitis Test (CMT) within three days after calving. The fresh samples were then plated on farm using a sterile cotton swab onto each half of a bi-plate. Plates were incubated overnight and then interpreted as 'no growth', when bacteria did not grow, or 'Gram-positive' or 'Gramnegative' depending if growth was on the Factor or the MacConkey media half of the bi-plate respectively. After plating, milk samples were frozen and later cultured in the laboratory using standard identification procedures. On farm culture results and corresponding in laboratory results are available from 80 quarter cases of clinical mastitis, and from 87 fresh cow CMT positive quarters. Using the on-farm culture method for clinical mastitis cases, producers were able to detect 83% of the Gram-positive cases (sensitivity), and classified correctly about 90% of the Gram-negative cases or cases where bacteria was not present (specificity). Consequently, 83% of the treated cases, 'Gram-positive' quarters underwent intramammary treatment, were truly Gram-positive (predictive value of a positive test; PV+), and 90% of the not treated cases, 'Gram-negative' or 'no growth', were truly uninfected or Gram-negative (predictive value of a negative test; PV-). For fresh cow CMT positive quarters, the sensitivity of the on-farm culture to detect gram-positive quarters was 88%, and the specificity was 70%. Accordingly, 80% of the treated cases were truly gram-positive (PV+), and 81% of the not treated cases were truly uninfected or Gram-negative (PV-). [ABSTRACT FROM AUTHOR]