Buczinski S, Vandeweerd J M
Département des Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, CP 5000, St-Hyacinthe, J2S 7C6, Québec, Canada.
Integrated Veterinary Research Unit, Namur Research Institute for Life Sciences, Department of Veterinary Medicine, Faculty of Sciences, Université de Namur, Rue de Bruxelles 61, 5000 Namur, Belgium.
J Dairy Sci. 2016 Sep;99(9):7381-7394. doi: 10.3168/jds.2016-10955. Epub 2016 Aug 8.
Provision of good quality colostrum [i.e., immunoglobulin G (IgG) concentration ≥50g/L] is the first step toward ensuring proper passive transfer of immunity for young calves. Precise quantification of colostrum IgG levels cannot be easily performed on the farm. Assessment of the refractive index using a Brix scale with a refractometer has been described as being highly correlated with IgG concentration in colostrum. The aim of this study was to perform a systematic review of the diagnostic accuracy of Brix refractometry to diagnose good quality colostrum. From 101 references initially obtain ed, 11 were included in the systematic review meta-analysis representing 4,251 colostrum samples. The prevalence of good colostrum samples with IgG ≥50g/L varied from 67.3 to 92.3% (median 77.9%). Specific estimates of accuracy [sensitivity (Se) and specificity (Sp)] were obtained for different reported cut-points using a hierarchical summary receiver operating characteristic curve model. For the cut-point of 22% (n=8 studies), Se=80.2% (95% CI: 71.1-87.0%) and Sp=82.6% (71.4-90.0%). Decreasing the cut-point to 18% increased Se [96.1% (91.8-98.2%)] and decreased Sp [54.5% (26.9-79.6%)]. Modeling the effect of these Brix accuracy estimates using a stochastic simulation and Bayes theorem showed that a positive result with the 22% Brix cut-point can be used to diagnose good quality colostrum (posttest probability of a good colostrum: 94.3% (90.7-96.9%). The posttest probability of good colostrum with a Brix value <18% was only 22.7% (12.3-39.2%). Based on this study, the 2 cut-points could be alternatively used to select good quality colostrum (sample with Brix ≥22%) or to discard poor quality colostrum (sample with Brix <18%). When sample results are between these 2 values, colostrum supplementation should be considered.
提供优质初乳（即免疫球蛋白G（IgG）浓度≥50g/L）是确保犊牛获得适当被动免疫转移的第一步。在农场中，很难对初乳中的IgG水平进行精确量化。使用糖度计通过白利糖度 scale评估折射率，已被描述为与初乳中的IgG浓度高度相关。本研究的目的是对用于诊断优质初乳的白利糖度折射法的诊断准确性进行系统评价。从最初获得的101篇参考文献中，11篇被纳入系统评价荟萃分析，代表4251份初乳样本。IgG≥50g/L的优质初乳样本的患病率在67.3%至92.3%之间（中位数为77.9%）。使用分层汇总接受者操作特征曲线模型，针对不同报告的临界点获得了准确性的具体估计值[敏感性（Se）和特异性（Sp）]。对于22%的临界点（n = 8项研究），Se = 80.2%（95%CI：71.1 - 87.0%），Sp = 82.6%（71.4 - 90.0%）。将临界点降低到18%会增加Se[96.1%（91.8 - 98.2%）]并降低Sp[54.5%（26.9 - 79.6%）]。使用随机模拟和贝叶斯定理对这些白利糖度准确性估计值的影响进行建模表明，白利糖度临界点为22%时的阳性结果可用于诊断优质初乳（优质初乳的检验后概率：94.3%（90.7 - 96.9%））。白利糖度值<18%时优质初乳的检验后概率仅为22.7%（12.3 - 39.2%）。基于本研究，这两个临界点可交替用于选择优质初乳（白利糖度≥22%的样本）或丢弃劣质初乳（白利糖度<18%的样本）。当样本结果介于这两个值之间时，应考虑补充初乳。
