Morrill K M, Robertson K E, Spring M M, Robinson A L, Tyler H D
Cornell Cooperative Extension, Ithaca, NY 14853.
Department of Animal Science, Iowa State University, Ames 50014.
J Dairy Sci. 2015 Jan;98(1):595-601. doi: 10.3168/jds.2014-8730. Epub 2014 Nov 20.
The objectives of this study were to (1) validate a method using refractometry to rapidly and accurately determine immunoglobulin (IgG) concentration in Jersey colostrum, (2) determine whether there should be different refractive index (nD) and %Brix cut points for Jersey colostrum, and (3) evaluate the effect of multiple freeze-thaw (FT) cycles on radial immunodiffusion (RID) and a digital refractometer to determine IgG concentration in Jersey colostrum. Samples (n=58; 3L) of colostrum were collected from a dairy in northwestern Iowa. Samples were analyzed within 2h of collection for IgG concentration by RID, %Brix, and nD by refractometer and an estimate of IgG by colostrometer. Samples were frozen, placed on dry ice, and transported to the laboratory at Iowa State University (Ames). Samples arrived frozen and were placed in a -20°C manual-defrost freezer until further analysis. On d 7 (1FT), d 14 (2FT), and 1yr (3FT) all samples were thawed, analyzed for IgG by RID, %Brix, nD by refractometer, and IgG estimate by colostrometer, and frozen until reanalysis at the next time point. Fresh colostrum had a mean (±SD) IgG concentration of 72.91 (±33.53) mg/mL, 21.24% (±4.43) Brix, and nD 1.3669 (±0.0074). Multiple FT cycles did affect IgG as determined by RID and colostrometer reading. The IgG concentrations were greater in fresh and 1FT samples as compared with 2FT and 3FT samples (72.91, 75.38, 67.20, and 67.31mg of IgG/mL, respectively). The colostrometer reading was lower in 1FT samples compared with fresh and 2FT samples. Multiple FT cycles had no effect on nD or %Brix reading. In fresh samples, IgG concentration was moderately correlated with nD (r=0.79), %Brix (r=0.79), and colostrometer reading (r=0.79). Diagnostic test characteristics using the recommended cut point of 1.35966 nD resulted in similar sensitivities for 1FT and 2 FT samples (94.87 and 94.74%, respectively). Cut points of 18 and 19% Brix resulted in the greatest sensitivities (92.31 and 84.62%) and specificity (94.74 and 94.74%, respectively). The 18% Brix cut point resulted in 94.83% of the samples being correctly classified based on IgG concentration. These data support the use of digital refractometer to accurately and rapidly determine IgG concentration in fresh Jersey colostrum. Additionally, these data suggest that IgG concentration determined by RID is affected by multiple FT cycles, whereas estimates obtained by refractometer are not affected by multiple FT cycles.
（1）验证一种使用折射仪快速准确测定泽西初乳中免疫球蛋白（IgG）浓度的方法；（2）确定泽西初乳是否应有不同的折射率（nD）和白利糖度切点；（3）评估多次冻融（FT）循环对放射免疫扩散法（RID）和数字折射仪测定泽西初乳中IgG浓度的影响。从爱荷华州西北部的一家奶牛场收集了初乳样本（n = 58；3L）。在采集后2小时内，通过RID分析IgG浓度，用折射仪测定白利糖度和nD，并通过初乳计估算IgG。样本被冷冻，置于干冰上，然后运至爱荷华州立大学（埃姆斯）的实验室。样本到达时处于冷冻状态，被放入-20°C的手动除霜冰箱中直至进一步分析。在第7天（1次冻融）、第14天（2次冻融）和第1年（3次冻融），所有样本解冻，通过RID分析IgG，用折射仪测定白利糖度和nD，并通过初乳计估算IgG，然后冷冻直至下一个时间点重新分析。新鲜初乳的平均（±标准差）IgG浓度为72.91（±33.53）mg/mL，白利糖度为21.24%（±4.43），nD为1.3669（±0.0074）。如通过RID和初乳计读数所确定的，多次冻融循环确实会影响IgG。与2次冻融和3次冻融样本相比，新鲜样本和1次冻融样本中的IgG浓度更高（分别为72.91、75.38、67.20和67.31mg IgG/mL）。与新鲜样本和2次冻融样本相比，1次冻融样本的初乳计读数更低。多次冻融循环对nD或白利糖度读数没有影响。在新鲜样本中，IgG浓度与nD（r = 0.79）、白利糖度（r = 0.79）和初乳计读数（r = 0.79）呈中度相关。使用推荐的1.35966 nD切点的诊断试验特征显示，1次冻融和2次冻融样本的敏感性相似（分别为94.87%和94.74%）。18%和19%白利糖度的切点导致最高的敏感性（分别为92.31%和84.62%）和特异性（分别为94.74%和94.74%）。18%白利糖度的切点使94.83%的样本根据IgG浓度被正确分类。这些数据支持使用数字折射仪准确快速地测定新鲜泽西初乳中的IgG浓度。此外，这些数据表明，通过RID测定的IgG浓度受多次冻融循环的影响，而通过折射仪获得的估算值不受多次冻融循环的影响。
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