Evaluation of an automated milk leukocyte differential test and the California Mastitis Test for detecting intramammary infection in early- and late-lactation quarters and cows
Evaluation of an automated milk leukocyte differential test and the California Mastitis Test for detecting intramammary infection in early- and late-lactation quarters and cows
复制标题
DOI：
10.3168/jds.2017-12548
复制
发表时间：
2017-08-01
影响因子：
3.5
通讯作者：
Green, H.
中科院分区：
文献类型：
--
作者：
Godden, S. M.;Royster, E.;Green, H.
研究目标是(1)描述自动牛奶白细胞鉴别(MLD)试验和加利福尼亚乳腺炎试验(CMT)的诊断试验特点，以确定奶牛在哺乳早期(EL)和哺乳期晚期(LL)的乳房感染(IMI)，以及(2)描述MLD检测结果在季度和奶牛水平上的重复性。从3个中西部牛群中抽取86头El和90头LL荷斯坦奶牛。采集四分之一的牛奶样本进行奶牛侧CMT测试、牛奶培养和MLD测试。通过3种方法确定四分之一IMI状态：单个牛奶样本培养、平行翻译重复样本培养和串联翻译重复样本培养。MLD检测在样本采集后8小时内一式两份完成；在每个可能的阈值设置(EL为1-18；LL为1-12)报告MLD结果(阳性/阴性)，并在每个可能的临界点(TRACE、>；=1、>；=2或3)报告CMT结果(阳性/阴性)。我们创建了2 x 2表格，将IMI的3种不同定义中的每一种作为参考测试，在季度和奶牛水平上将MLD和CMT结果与牛奶培养进行比较。将配对的MLD测试结果与评估重复性进行比较。最大似然比试验显示出良好的重复性。牛奶培养中IMI定义的选择对MLD和CMT测试特性的估计影响较小。对于EL样本，在四分之一水平上解释MLD和CMT结果时，无论使用哪种参照测试，这两种测试的敏感性都很低(MLD=11.7-39.1%；CMT=0-52.2%)，但特异性很好(MLD=82.1-95.2%；CMT=68.1-100%)，这取决于所使用的切入点。如果在奶牛水平上解释诊断，敏感性略有提高(MLD=25.6-56.4%；CMT=0-72.2%)，但特异性通常会下降(MLD=61.8-100%；CMT=25.0-100%)，这取决于所使用的切入点。对于LL样本，当解释到四分之一水平时，两种测试都具有可变的敏感性(MLD=46.6-84.8%；CMT=9.6-72.7%)和可变的特异性(MLD=59.2-79.8%；CMT=52.5-97.3%)，这取决于所使用的切入点。如果在奶牛水平上解释，则检测灵敏度提高(MLD=59.6-86.4%；CMT=19.1-86.4%)，尽管特异性下降(MLD=32.4-56.8%；CMT=14.3-92.3%)。考虑采用LL或EL筛选计划的测试的生产商在决定解释级别(四分之一或COW)以及选择解释测试结果的最佳切入点时，需要仔细考虑该计划的目标和优先顺序(例如，是否优先考虑测试灵敏度或特异度)。还需要更多的验证性研究和大规模的随机实地研究，以评估选择性干牛治疗或新鲜奶牛筛查计划中采用的测试对乳房健康、抗生素使用和经济学的影响。
Study objectives were to (1) describe the diagnostic test characteristics of an automated milk leukocyte differential (MLD) test and the California Mastitis Test (CMT) to identify intramammary infection (IMI) in early- (EL) and late-lactation (LL) quarters and cows when using 3 different approaches to define IMI from milk culture, and (2) describe the repeatability of MLD test results at both the quarter and cow level. Eighty-six EL and 90 LL Holstein cows were sampled from 3 Midwest herds. Quarter milk samples were collected for a cow-side CMT test, milk culture, and MLD testing. Quarter IMI status was defined by 3 methods: culture of a single milk sample, culture of duplicate samples with parallel interpretation, and culture of duplicate samples with serial interpretation. The MLD testing was completed in duplicate within 8 h of sample collection; MLD results (positive/negative) were reported at each possible threshold setting (1-18 for EL; 1-12 for LL) and CMT results (positive/negative) were reported at each possible cut-points (trace, >= 1, >= 2, or 3). We created 2 x 2 tables to compare MLD and CMT results to milk culture, at both the quarter and cow level, when using each of 3 different definitions of IMI as the referent test. Paired MLD test results were compared with evaluate repeatability. The MLD test showed excellent repeatability. The choice of definition of IMI from milk culture had minor effects on estimates of MLD and CMT test characteristics. For EL samples, when interpreting MLD and CMT results at the quarter level, and regardless of the referent test used, both tests had low sensitivity (MLD = 11.7-39.1%; CMT = 0-52.2%) but good to very good specificity (MLD = 82.1-95.2%; CMT = 68.1-100%), depending on the cut-point used. Sensitivity improved slightly if diagnosis was interpreted at the cow level (MLD = 25.6-56.4%; CMT = 0-72.2%), though specificity generally declined (MLD = 61.8-100%; CMT = 25.0-100%) depending on the cut-point used. For LL samples, when interpreted at the quarter level, both tests had variable sensitivity (MLD = 46.6-84.8%; CMT = 9.6-72.7%) and variable specificity (MLD = 59.2-79.8%; CMT = 52.5-97.3%), depending on the cut-point used. Test sensitivity improved if interpreted at the cow level (MLD = 59.6-86.4%; CMT = 19.1-86.4%), though specificity declined (MLD = 32.4-56.8%; CMT = 14.3-92.3%). Producers considering adopting either test for LL or EL screening programs will need to carefully consider the goals and priorities of the program (e.g., whether to prioritize test sensitivity or specificity) when deciding on the level of interpretation (quarter or cow) and when selecting the optimal cut-point for interpreting test results. Additional validation studies and large randomized field studies will be needed to evaluate the effect of adopting either test in selective dry cow therapy or fresh cow screening programs on udder health, antibiotic use, and economics.