Abstract
BackgroundSubclinical mastitis (SCM) and intramammary infection (IMI) increase the sodium (Na) concentration and electrical conductivity (EC) and decrease the potassium (K) and calcium (Ca) concentrations in glandular secretions of lactating dairy cattle.HypothesisLow‐cost portable Na, K, Ca, and EC meters are clinically useful cow‐side tests for diagnosing SCM and IMI.AnimalsOne hundred fifteen dairy cows at dry off and 92 cows within 4‐7 days postcalving.MethodsQuarter foremilk samples were obtained and the somatic cell count (SCC) was measured using a DeLaval cell counter with SCM defined as SCC ≥ 200 000 cells/mL. Microbiological culture of foremilk samples was used to diagnose IMI. Cisternal milk Na, K, and Ca concentrations and EC were measured using portable ion‐selective meters. Logistic regression was used to determine the area under the receiver operating characteristic curve (AUC) and the optimal cut point was determined using Youden's index. Diagnostic test performance was evaluated by comparing the AUC and calculating the sensitivity, specificity, and positive likelihood ratio (+LR) at the optimal cut point for SCM and IMI.ResultsDiagnostic test performance was much better when the meters were used to diagnose SCM as compared to IMI. Cisternal milk Na concentration provided the most accurate method for identifying quarters with SCM or IMI. However, AUC was <0.90 and +LR was <10 for all diagnostic test evaluations.Conclusions and Clinical ImportanceCisternal milk Na, K, and Ca concentrations and EC were not sufficiently predictive of SCM or IMI to be recommended as clinically useful diagnostic tests.
Highlights
Accurate identification of cows with subclinical mastitis (SCM) or intramammary infection (IMI) at dry off or early lactation is an important goal of mastitis control programs and a fundamental requirement for implementing selective dry cow treatment.[1]
We compared the clinical utility of using portable low-cost meters that measure milk electrical conductivity (EC) and milk sodium concentration (Na), K, and Ca concentrations as on-farm or cow-side tests for diagnosing Subclinical mastitis (SCM) and IMI at dry off and freshening
Our results indicated that the median EC for milk from healthy quarters at 37C was 4.5 mS/cm, and that EC provided a moderately accurate method for diagnosing SCM at an optimal cut point of >5.2 mS/cm at dry off and >4.9 mS/cm at freshening
Summary
Accurate identification of cows with subclinical mastitis (SCM) or intramammary infection (IMI) at dry off or early lactation is an important goal of mastitis control programs and a fundamental requirement for implementing selective dry cow treatment.[1]. The low-cost (approximately $250 US) and portability of the meters, as well as their ability to measure cation concentrations or EC in uncentrifuged milk samples, make them very attractive for on-farm or cow-side use. Studies conducted by our laboratory over the past 5 years have validated the accuracy of Na and K LAQUAtwin meters in measuring unbound Na and K concentrations in bovine cisternal milk.[19,20]. The Ca LAQUAtwin meter has been used to measure ionized Ca concentration in bovine milk.[21,22] Based on these findings, we hypothesized that measuring cisternal milk Na and K concentrations using LAQUAtwin meters would provide accurate, low-cost, and practical methods for diagnosing SCM and IMI in dairy cattle. Our objectives were to determine and compare the accuracy of LAQUAtwin portable EC, Na, K, and Ca meters for diagnosing SCM and IMI in dairy cattle
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