Application and validation of the systemic severity score system for acute coliform mastitis in dairy cattle from farms of various types and sizes

Abstract

　Given the high mortality and cull rates of dairy cows affected by severe, acute coliform mastitis（ACM）, a rapid severity assessment is important. The systemic severity score（SSS）system allows a rapid evaluation of disease severity based on the four systemic disease signs of ACM, i.e., rectal temperature, hydration status, rumen contraction rate and attitude （each scored from 0 to 2 or 3; total score of 0-2 = mild, 3-5 = moderate and 6-9 = severe）. It is one of the few scoring systems with a demonstrated correlation with the severity. However, the system was developed based on the data of six large-scale farms in the United States, and thus its usefulness for different or mixed types and sizes of dairy operation has been disputed. The purpose of the present study was to evaluate the usefulness of the SSS system in our farm-visit area by analyzing farm sizes, barn styles and cow removal rates within 100 days of the first visit using receiver operating characteristic （ROC） curves and survival times analyses.

　A total of 90 cases of ACM from 39 farms were included in the study. Of those, 79 cows from 37

farms were from <200-cow operations, and 64 cows from 29 farms were kept in tie-stall barns. All cows were not vaccinated against ACM and had an SSS score of 4 or higher. A total of 78 cows were removed, and we found that the removal rate increased with the increase in the SSS score at the first visit. When animals above the optimal cutoff value（score 6）, determined by the removal prediction by the ROC analysis, were compared to those below the cutoff value, the relative risk ratio of death and removal was 3.7［95% confidence interval（CI）, 1.2-12.0］ and 2.6（95% CI, 1.1-5.8）, respectively. The survival time analysis using removal as an endpoint showed that the survival rate remained significantly lower in cows with a score of ≥6 than those with a score of ≤5 （59 vs. 86%; hazard ratio, 3.5, CI, 1.4-8.8）. These results suggest that the SSS system could be applied to unvaccinated ACM cases from farms of various sizes and types to determine the severity of the disease.