Department of Animal Science, Cornell University, Ithaca, NY 14850.
Department of Animal Sciences, University of Florida, Gainesville 32611.
J Dairy Sci. 2017 Sep;100(9):7211-7226. doi: 10.3168/jds.2016-12531. Epub 2017 Jun 28.
Microbial samples from 4 independent experiments in lactating dairy cattle were obtained and analyzed for nutrient composition, AA digestibility, and AA profile after multiple hydrolysis times ranging from 2 to 168 h. Similar bacterial and protozoal isolation techniques were used for all isolations. Omasal bacteria and protozoa samples were analyzed for AA digestibility using a new in vitro technique. Multiple time point hydrolysis and least squares nonlinear regression were used to determine the AA content of omasal bacteria and protozoa, and equivalency comparisons were made against single time point hydrolysis. Formalin was used in 1 experiment, which negatively affected AA digestibility and likely limited the complete release of AA during acid hydrolysis. The mean AA digestibility was 87.8 and 81.6% for non-formalin-treated bacteria and protozoa, respectively. Preservation of microbe samples in formalin likely decreased recovery of several individual AA. Results from the multiple time point hydrolysis indicated that Ile, Val, and Met hydrolyzed at a slower rate compared with other essential AA. Singe time point hydrolysis was found to be nonequivalent to multiple time point hydrolysis when considering biologically important changes in estimated microbial AA profiles. Several AA, including Met, Ile, and Val, were underpredicted using AA determination after a single 24-h hydrolysis. Models for predicting postruminal supply of AA might need to consider potential bias present in postruminal AA flow literature when AA determinations are performed after single time point hydrolysis and when using formalin as a preservative for microbial samples.
从 4 头泌乳奶牛中获得了 4 份独立的微生物样本，并对其营养成分、AA 消化率和在 2 至 168 小时的多次水解时间范围内的 AA 谱进行了分析。所有分离物都使用了类似的细菌和原生动物分离技术。采用新的体外技术分析瘤胃细菌和原生动物的 AA 消化率。采用多次水解和最小二乘非线性回归法确定瘤胃细菌和原生动物的 AA 含量，并与单次水解进行等效性比较。在 1 个实验中使用了福尔马林，它会降低 AA 消化率，并且可能会在酸水解过程中限制 AA 的完全释放。未经福尔马林处理的细菌和原生动物的 AA 消化率平均值分别为 87.8%和 81.6%。福尔马林对微生物样品的保存可能会降低几种单独 AA 的回收率。多次水解的结果表明，与其他必需 AA 相比，Ile、Val 和 Met 的水解速度较慢。考虑到估计微生物 AA 谱中生物学上重要的变化，单次水解与多次水解不等效。使用 24 小时单一水解后进行 AA 测定时，Met、Ile 和 Val 等几种 AA 被低估。当在单次水解后进行 AA 测定并且使用福尔马林作为微生物样品的防腐剂时，预测 AA 在后肠道供应的模型可能需要考虑在后肠道 AA 流动文献中存在的潜在偏差。
