Evaluation of 3 esterase tests for the diagnosis of subclinical mastitis at dry-off and freshening in dairy cattle

摘要

Subclinical mastitis (SCM) and intramammary infection(IMI) increase esterase activity in the glandularsecretions of dairy cattle. Our objective was to evaluatethe clinical performance of 3 commercially availableesterase tests for diagnosing SCM and IMI. Foremilksamples were collected from 380 quarters (96 cows) atdry-off and from 329 quarters (83 cows) within 4 to7 d after calving. Quarter somatic cell count (SCC)was measured using the reference method (DeLaval cellcounter; De Laval International AB, Tumba, Sweden)with SCM defined as SCC >200,000 cells/mL. Bacterialculture of foremilk samples was used to diagnose IMIbased on the growth of ≥100 cfu/mL. The SCC wasestimated using 3 PortaSCC tests (PortaCheck, Moorestown,NJ) from the measured esterase activity and theCalifornia Mastitis Test (CMT). Clinical performancewas evaluated using logistic regression to determine thearea under the receiver operating characteristic curve(AUC) and identify test sensitivity (Se) and specificity(Sp) at the optimal cut-point for diagnosing SCMand IMI. Test agreement was also evaluated using thekappa coefficient (κ) and weighted κ. The PortaSCCcolor test was the best-performing PortaSCC test fordiagnosing SCM at dry-off (AUC = 0.90, Se = 0.91, Sp= 0.81, κ = 0.71) and at freshening (AUC = 0.86, Se= 0.74, Sp = 0.95, κ = 0.72), at an optimal cut-pointof ≥250,000 cells/mL but required 45 min to producea result. For comparison, the CMT required 2 min toproduce a result and a CMT score of trace or higherwas superior to the PortaSCC color test for diagnosingSCM at dry-off (AUC = 0.95, Se = 0.95, Sp = 0.86,κ = 0.81) and freshening (AUC = 0.88, Se = 0.79, Sp= 0.95, κ = 0.76). The PortaSCC quick test was thebest-performing PortaSCC test for diagnosing IMI atdry-off (AUC = 0.81, Se = 0.81, Sp = 0.78 κ = 0.40)and required 5 min to produce a result, whereas thePortaSCC color test was the best performing PortaSCCtest for diagnosing IMI at freshening (AUC = 0.80, Se= 0.75, Sp = 0.79 κ = 0.38). For comparison, the CMTwas inferior to the PortaSCC quick test for diagnosingIMI at dry-off (AUC = 0.73, Se = 0.76, Sp = 0.60,κ = 0.20) but was equivalent to the PortaSCC colortest at freshening (AUC = 0.79, Se = 0.58, Sp = 0.93,κ = 0.50). The PortaSCC color and quick tests andCMT were considered good tests for diagnosing SCMand IMI because clinically useful tests typically have anAUC >0.80 and κ >0.6. Based on the test sensitivity,cost, and analysis time, there does not appear to be apersuasive reason to select the PortaSCC tests over thetraditional CMT for diagnosing SCM and IMI.