Hawkins D
a Franklin Vets , Waiuku , New Zealand.
N Z Vet J. 2019 Jul;67(4):203-209. doi: 10.1080/00480169.2019.1608872.
To assess the use of different cut-points based on individual cow somatic cell counts (SCC) to define cows with intramammary infection (IMI) at drying-of, in a herd with a high mean bulk tank SCC. Results for SCC from four herd tests during lactation and bacterial culture of milk samples collected before drying-off were obtained for 139 cows from a herd with an average bulk milk SCC of >300,000 cells/mL over the final 4 months of the 2006/07 lactation. Based on culture results, cows were defined as being infected with a major (, or spp.) or any pathogen. Receiver-operator characteristics (ROC) curves were used to determine optimum cut-points for maximum, average and last herd test SCC, for predicting IMI. Multivariable logistic regression models were used to determine which variables were associated with IMI, and the sensitivity (Se), specificity (Sp) and positive predictive value (PPV) were determined for different cut-points. At the cow level, 75/139 (54.0%) cows had IMI with a major pathogen and 123/139 (88.5%) with any pathogen. A SCC ≥150,000 cells/mL at ≥2 herd tests and a SCC ≥299,000 cells/mL at the last herd test, for cows aged ≥4 years, were associated with IMI with a major pathogen at drying-off (p<0.05). A SCC ≥150,000 cells/mL at ≥2 herd tests was associated with IMI with any pathogen at drying-off (p<0.001). A cut-point of ≥150,000 cells/mL at any herd test had the highest Se (0.97 and 0.94), but the lowest Sp (0.19 and 0.44) and PPV (0.58 and 0.93) for infection with major and any pathogens, respectively. A cut-point of ≥150,000 cells/mL at ≥2 herd tests doubled the Sp and increased the PPV without large decreases in test Se for infection with either a major or any pathogen. In this herd with a high bulk milk SCC, use of a cut-point of a SCC ≥150,000 cells/mL at any herd test to define IMI would be appropriate, where the goal at drying-off is to ensure that cows infected with any pathogen receive antimicrobial treatment. Where the goal is to reduce the use of antimicrobial dry cow therapy in uninfected cows while limiting the number of infected cows not being treated, use of a cut-point of SCC ≥150,000 cells/mL at ≥2 herd tests to define IMI may be more appropriate.
为评估在一个平均批量奶罐体细胞计数（SCC）较高的牛群中，基于个体奶牛体细胞计数（SCC）使用不同切点来定义干奶期患有乳房内感染（IMI）的奶牛。从一个在2006/07泌乳期最后4个月平均批量奶SCC>300,000个细胞/毫升的牛群中，获取了139头奶牛在泌乳期4次牛群检测的SCC结果以及干奶前采集的牛奶样本的细菌培养结果。根据培养结果，奶牛被定义为感染主要病原体（金黄色葡萄球菌、无乳链球菌或停乳链球菌）或任何病原体。采用受试者工作特征（ROC）曲线来确定用于预测IMI的最大、平均和最后一次牛群检测SCC的最佳切点。使用多变量逻辑回归模型来确定哪些变量与IMI相关，并确定不同切点的敏感性（Se）、特异性（Sp）和阳性预测值（PPV）。在个体奶牛水平上，139头奶牛中有75头（54.0%）感染主要病原体的IMI，123头（88.5%）感染任何病原体的IMI。对于年龄≥4岁的奶牛，在≥2次牛群检测时SCC≥150,000个细胞/毫升以及在最后一次牛群检测时SCC≥299,000个细胞/毫升，与干奶期感染主要病原体的IMI相关（p<0.05）。在≥2次牛群检测时SCC≥150,000个细胞/毫升与干奶期感染任何病原体的IMI相关（p<0.001）。对于感染主要病原体和任何病原体，在任何一次牛群检测时切点≥150,000个细胞/毫升分别具有最高的Se（0.97和0.94），但最低的Sp（0.19和0.44）和PPV（0.58和0.93）。在≥2次牛群检测时切点≥150,000个细胞/毫升，对于感染主要病原体或任何病原体，使Sp翻倍并提高了PPV，而检测Se没有大幅下降。在这个平均批量奶SCC较高的牛群中，如果干奶期的目标是确保感染任何病原体的奶牛接受抗菌治疗，那么使用在任何一次牛群检测时SCC≥150,000个细胞/毫升的切点来定义IMI是合适的。如果目标是减少未感染奶牛的抗菌干奶牛治疗使用量，同时限制未接受治疗的感染奶牛数量，那么使用在≥2次牛群检测时SCC≥150,000个细胞/毫升的切点来定义IMI可能更合适。
