Association of Differential Somatic Cell Count with Antibiotic Success Following an Intramammary Infection

Historically, methods to detect subclinical mastitis have been used to aid treatment decisions. The limitations of these tests have led to the exploration of the use of differential somatic cell count (DSCC). The objective of this study was to evaluate the relationship between DSCC and antibiotic success in subclinically infected cows. Cows were pre-screened to confirm an SCC ≥ 200,000 cells/mL and a positive bacterial culture. At enrollment, aseptic quarter milk samples were collected for culturing and evaluated using SCC, DSCC, the California Mastitis Test (CMT), and electrical conductivity. Enrolled quarters were treated with an intramammary antibiotic and resampled 7-, 14-, 28-, and 35-days post-treatment and retrospectively classified as “Cured” or failed to cure (Failed) based on a bacteriological cure. The overall cure rate was 51.5%. Pre-treatment SCC, total leukocyte count (TLC), neutrophils, and CMT were lower in Cured quarters compared to Failed. Meanwhile, macrophage percentage was greater in Cured quarters compared to Failed. No difference was found between lymphocyte percentage and conductivity. When evaluating the use of multiple threshold optimizations to predict cure outcome, TLC tended to have the highest ranking for the metric of interest; however, SCC tended to numerically perform as well in sensitivity and specificity outside of the optimized parameter.