Comparative Evaluation of Some Diagnostic Tests for on-farm Screening of Subclinical Mastitis in Crossbreed Dairy Cows

Subclinical mastitis is a costly disease for dairy cattle worldwide due to economic losses from reduced milk yield, veterinary costs, and premature culling; thus, regular screening is of paramount importance for early detection, prompt treatment, and effective control measures. This study was conducted to assess the possible risk factors and compare the efficiency of three indirect mastitis diagnostic tests for their ability to classify correctly under health status in individual cows. Seven hundred and forty-two milk samples from 186 lactating cows kept in six farms were screened for subclinical mastitis using Sodium Lauryl Sulfate (SLS), California Mastitis Test (CMT), and Somatic Cell Count (SCC). The research revealed moderate overall prevalence (21.5%) of farm-level subclinical mastitis with high (65.2%) prevalence in farm B and low (10.7%) in farm F. Specific test-based results were 36.56%, 36.56% and 21.51% for SLT, CMT and SCC, respectively. There was a statistical difference (p=0.0001) between SCC and SLS and between SCC and CMT, but no significant differences (p=0.57) were observed between SLS and CMT. Quarter subclinical mastitis prevalence for SLS, CMT, and SCC was 16.85% (95% CI: 14.3-19.7), 15.77% (95% CI: 13.1-18.3), and 8.45% (95% CI: 6.4-10.5), respectively. Both SLS and CMT demonstrated strong sensitivity (100% and 90.48%) and specificity (90.72% and 91.16%) compared to the SCC test. Positive predictive values for SLS and CMT were 50% and 48.72%, respectively, whereas negative predictive values for SLS and CMT were 100% and 99.04%. Cohen’s Kappa of SLS was 0.62, while CMT showed 0.58. The area under the receiver operating characteristic curve for SLS and CMT was 0.996 and 0.997, respectively. The diagnostic accuracy of SLS and CMT were 91.51 and 91.11, respectively. Based on the diagnostic efficiency of SLS in terms of sensitivity, specificity, predictive values, and kappa index, it is suggested that SLS can be used as an alternative to CMT for animal-side subclinical mastitis diagnostic tests.