Amino acid composition of rumen bacteria and protozoa in cattle

Abstract

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.

Post‐ruminal non‐protein nitrogen supplementation as a strategy to improve fibre digestion and N efficiency in the ruminant

“…Differences between UR150 and UA150 in our second study are indications of decreased ruminal stability (De Veth & Kolver, 2001) and the potential for reduced N incorporation into microbial protein (Kang-Meznarich & Broderick, 1980;Marini & Van Amburgh, 2003). Estimated crude microbial protein produced per kilogram of digestible organic matter is a critical parameter in the evaluation of treatment response in the current experimental setting, as microbial protein supply accounts for up to 50% of total crude protein supply in the ruminant (Sok et al, 2017). That this parameter was not different between UR50 and UA150 provides evidence that the ruminal supply of N was sufficient to support microbial growth and fermentation activity.…”

“…The inclusion of dietary non-protein nitrogen is unique to ruminant nutrition and facilitates microbial fermentation processes towards the generation of protein supply for the host (Sok, Ouellet, Firkins, Pellerin, & Lapierre, 2017;Virtanen, 1966).…”

Amino acid profiles of rumen undegradable protein: a comparison between forages including cereal straws and alfalfa and their respective total mixed rations

“…In this study, the AA composition in forages and TMR‐based diets tends to differ significantly after correction except for alfalfa hay, which demonstrates that the method used for correcting for microbial contamination is essential to clarify and predict accurate AA profiles of RUP. The comparison between AA profiles of microbial protein (Sok, Ouellet, Firkins, Pellerin, & Lapierre, ) and AA profiles of alfalfa hay after rumen incubation indicated that most of the AAs were similar between these two items, but Gly, Ser, Met and Tyr were different. Thus, we speculated that no significant differences found between the microbial corrected and uncorrected AA profile of alfalfa hay, which was mainly due to the similar AA profile of microbial protein and of alfalfa hay.…”

Aspartate metabolism is involved in the maintenance of enterohaemorrhagic Escherichia coli O157:H7 in bovine intestinal content

“…However, except in the rumen, very little is known about the composition and the level of amino acid in the gut of cattle as well as their metabolism by the endogenous microbiota. The amino acids found in highest concentrations in BSIC in the present work appear to be also main constituents of rumen microbial proteins, aspartate and glutamate being the major ones (Sok et al, ). In addition to amino acids of microbial origin, amino acids such as aspartate and serine are abundantly present in the mucus layer covering the bovine gut (Montagne et al, ) and are constantly released in the intestinal lumen during cell renewal.…”

“…Because of the high proteolytic activity of the rumen microbiota, relatively few dietary proteins and amino acids reach the lower gastrointestinal tract of ruminants (Wallace, 1996). The main protein sources for these animals are rumen microbial proteins which flow with the digesta to the lower digestive tract (Sok et al, 2017). However, except in the rumen, very little is known about the composition and the level of amino acid in the gut of cattle as well as their metabolism by the endogenous microbiota.…”