Department of Animal Sciences, University Laval, Québec, QC, Canada, G1V 0A6.
Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada, J1M 0C8.
J Dairy Sci. 2017 Jul;100(7):5241-5249. doi: 10.3168/jds.2016-12447. Epub 2017 May 10.
Because microbial crude protein (MCP) constitutes more than 50% of the protein digested in cattle, its AA composition is needed to adequately estimate AA supply. Our objective was to update the AA contributions of the rumen microbial AA flowing to the duodenum using only studies from cattle, differentiating between fluid-associated bacteria (FAB), particle-associated bacteria (PAB), and protozoa, based on published literature (53, 16, and 18 treatment means were used for each type of microorganism, respectively). In addition, Cys and Met reported concentrations were retained only when an adequate protection of the sulfur groups was performed before the acid hydrolysis. The total AA (or true protein) fraction represented 82.4% of CP in bacteria. For 10 AA, including 4 essential AA, the AA composition differed between protozoa and bacteria. The most noticeable differences were a 45% lower Lys concentration and 40% higher Ala concentration in bacteria than in protozoa. Differences between FAB and PAB were less pronounced than differences between bacteria and protozoa. Assuming 33% FAB, 50% PAB, and 17% of protozoa in MCP duodenal flow, the updated concentrations of AA would decrease supply estimates of Met, Thr, and Val originating from MCP and increase those of Lys and Phe by 5 to 10% compared with those calculated using the FAB composition reported previously. Therefore, inclusion of the contribution of PAB and protozoa to the duodenal MCP flow is needed to adequately estimate AA supply from microbial origin when a factorial method is used to estimate duodenal AA flow. Furthermore, acknowledging the fact that hydrolysis of 1 kg of true microbial protein yields 1.16 kg of free AA substantially increases the estimates of AA supply from MCP.
由于微生物粗蛋白 (MCP) 构成了牛消化蛋白质的 50%以上，因此需要其氨基酸组成来充分估计氨基酸的供应。我们的目的是使用仅来自牛的研究，根据已发表的文献（分别为每种微生物使用 53、16 和 18 个处理平均值），更新瘤胃微生物氨基酸流向十二指肠的氨基酸贡献，区分流体相关细菌 (FAB)、颗粒相关细菌 (PAB) 和原生动物。此外，仅当在酸水解之前对硫基团进行充分保护时，才保留报告的 Cys 和 Met 浓度。总氨基酸 (或真蛋白) 部分占细菌中 CP 的 82.4%。对于 10 种氨基酸，包括 4 种必需氨基酸，原生动物和细菌的氨基酸组成不同。最明显的差异是细菌中 Lys 浓度比原生动物低 45%，Ala 浓度比原生动物高 40%。FAB 和 PAB 之间的差异不如细菌和原生动物之间的差异明显。假设 MCP 十二指肠流量中 33%为 FAB、50%为 PAB 和 17%为原生动物，则更新后的 AA 浓度将降低源自 MCP 的 Met、Thr 和 Val 的供应估计值，并将 Lys 和 Phe 的供应估计值提高 5%至 10%，与以前使用 FAB 组成计算相比。因此，当使用因子法估计十二指肠 AA 流量时，需要纳入 PAB 和原生动物对 MCP 十二指肠流量的贡献，以充分估计微生物来源的 AA 供应。此外，认识到水解 1 千克真微生物蛋白质可产生 1.16 千克游离氨基酸，这大大增加了 MCP 中氨基酸供应的估计值。
