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

Four subclinical mastitis diagnostic tests (the UdderCheck (R) test [a lactate dehydrogenase-based test], the California Mastitis Test [CMT], the Draminski (R) test [a conductivity-based test] and the PortaSCC (R) 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 (R) and UdderCheck (R) tests were compared with the PortaSCC (R) as reference. The CMT, Draminski (R) and UdderCheck (R) test results were compared with the results of the PortaSCC (R) 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 (R)) and 64.00% and 78.95% (UdderCheck (R)). The CMT showed substantial agreement (k = 0.66), the Draminski (R) test showed moderate agreement (k = 0.48) and the UdderCheck (R) test showed fair agreement (k = 0.37) with the PortaSCC (R) 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 (R), CMT, Draminski (R) and UdderCheck (R) tests, respectively. At udder quarter level, subclinical mastitis prevalence was 20%, 21.67% and 20.83% for PortaSCC (R), CMT and UdderCheck (R), 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 (R) test, the CMT was the most preferable option, followed by the Draminski (R) test, while the UdderCheck (R) test was the least preferable option for subclinical mastitis screening.