Comparison of cow-side diagnostic tests for subclinical mastitis of dairy cows in Musanze district, Rwanda

Four subclinical mastitis diagnostic tests (the UdderCheck(®) test [a lactate dehydrogenase-based test], the California Mastitis Test [CMT], the Draminski(®) test [a conductivity-based test] and the PortaSCC(®) test [a portable somatic cell count-based test]) were compared in a study comprising crossbreed dairy cows (n = 30) during September and October 2015. Sensitivity and specificity of the CMT, Draminski(®) and UdderCheck(®) tests were compared with the PortaSCC(®) as reference. The CMT, Draminski(®) and UdderCheck(®) test results were compared with the results of the PortaSCC(®) test using kappa statistics. Duplicate quarter milk samples (n = 120) were concurrently subjected to the four tests. Sensitivity and specificity were 88.46% and 86.17% (CMT), 78.5% and 81.4% (Draminski(®)) and 64.00% and 78.95% (UdderCheck(®)). The CMT showed substantial agreement (k = 0.66), the Draminski(®) test showed moderate agreement (k = 0.48) and the UdderCheck(®) test showed fair agreement (k = 0.37) with the PortaSCC(®) test and positive likelihood ratios were 6.40, 4.15 and 3.04, respectively. The cow-level subclinical mastitis prevalence was 70%, 60%, 60% and 56.7% for PortaSCC(®), CMT, Draminski(®) and UdderCheck(®) tests, respectively. At udder quarter level, subclinical mastitis prevalence was 20%, 21.67% and 20.83% for PortaSCC(®), CMT and UdderCheck(®), respectively. A correlation (P < 0.05) and moderate strength of association were found between the four tests used. The study showed that compared to the PortaSCC(®) test, the CMT was the most preferable option, followed by the Draminski(®) test, while the UdderCheck(®) test was the least preferable option for subclinical mastitis screening.