Cornell Cooperative Extension, Cornell University, Ithaca, NY14853, USA.
J Dairy Sci. 2012 Jul;95(7):3987-96. doi: 10.3168/jds.2011-5104.
Our objectives were to evaluate the use of refractometry as a means of estimating immunoglobulin G (IgG) concentration of bovine maternal colostrum (MC) and determine if fractionation of MC using caprylic acid (CA) improved estimates of IgG. Samples (n=85) of MC were collected from a single dairy in California and used to determine the method of CA fraction that produced the best prediction of IgG based on CA fractionation followed by refractometry. Subsequently, samples of MC (n=827) were collected from 67 farms in 12 states to compare refractometry with or without CA fractionation as methods to estimate IgG concentration. Samples were collected from the feeding pool and consisted of fresh (n=196), previously frozen (n=479), or refrigerated (n=152) MC. Samples were further classified by the number freeze-thaw cycles before analysis. Fractionation with CA was conducted by adding 1 mL of MC to a tube containing 75 μL of CA and 1 mL of 0.06 M acetic acid. The tube was shaken and allowed to react for 1 min. Refractive index of the IgG-rich supernatant (nDf) was determined using a digital refractometer. Whole, nonfractionated MC was analyzed for IgG by radial immunodiffusion (RID) and refractive index (nDw). The relationship between nDf and IgG (r=0.53; n=805) was weak, whereas that between nDw and IgG was stronger (r=0.73; n=823). Fresh samples analyzed by refractometry that subsequently went through 1 freeze-thaw cycle before RID analysis resulted in the strongest relationship between IgG and nDf or nDw (r=0.93 and 0.90, respectively). The MC samples collected fresh on the farm but frozen 2 or more times before analysis by refractometry or RID had low correlations between IgG and nDf and nDw (r=0.09 and 0.01). Samples refrigerated or frozen on the farm before analysis had weaker relationships between RID and nDf or nDw (r=0.38 to 0.80), regardless of the number of freeze-thaw cycles. Breed and lactation number did not affect the accuracy of either test. These results indicated that refractometry, without or with CA fractionation, was an accurate and rapid method to determine IgG concentration when samples of MC were not previously stored before refractometry and frozen only once before RID analysis.
我们的目标是评估折光法作为一种估计牛初乳 (MC) 免疫球蛋白 G (IgG) 浓度的方法，并确定使用辛酸 (CA) 对 MC 进行分级是否可以改善 IgG 的估计值。从加利福尼亚州的一家奶牛场采集了 85 份 MC 样本，用于确定基于 CA 分级随后进行折光法的最佳 IgG 预测值的 CA 分级方法。随后，从 12 个州的 67 个农场采集了 827 份 MC 样本，以比较折光法是否与 CA 分级结合作为估计 IgG 浓度的方法。样品取自喂养池，由新鲜（n=196）、先前冷冻（n=479）或冷藏（n=152）MC 组成。样品根据分析前的冻融循环次数进一步分类。CA 分级是通过将 1 毫升 MC 加入含有 75 微升 CA 和 1 毫升 0.06 M 乙酸的管中进行的。将管摇匀并反应 1 分钟。使用数字折射计测定富含 IgG 的上清液的折射率（nDf）。全部分级和非分级的 MC 通过放射免疫扩散（RID）和折射率（nDw）分析 IgG。nDf 与 IgG 之间的关系（r=0.53；n=805）较弱，而 nDw 与 IgG 之间的关系较强（r=0.73；n=823）。用折射法分析后仅经过 1 次冻融循环的新鲜样品，导致 IgG 与 nDf 或 nDw 之间的关系最强（r=0.93 和 0.90）。在分析前在农场新鲜采集但经过 2 次或更多次冷冻的 MC 样本，与 nDf 和 nDw 之间的 IgG 相关性较低（r=0.09 和 0.01）。在分析前在农场冷藏或冷冻的样本，与 RID 和 nDf 或 nDw 的关系较弱（r=0.38 至 0.80），无论冻融循环次数如何。品种和泌乳次数均不影响两种检测方法的准确性。这些结果表明，折射法，无论是否使用 CA 分级，都是一种准确快速的方法，可以在 MC 样本在折射法之前没有预先储存且仅在 RID 分析之前冷冻一次时确定 IgG 浓度。
