Bacteria that colonize the mammalian intestine collectively possess a far larger repertoire of degradative enzymes and metabolic capabilities than their hosts. Microbial fermentation of complex non...

https://www.tandfonline.com/doi/pdf/10.4161/gmic.19897

Microbial degradation of complex carbohydrates in the gut

Effects and fate of tannins in ruminant animals, adaptation to tannins, and strategies to overcome detrimental effects of feeding tannin-rich feeds

Starch is the major energy component of grains. Wheat contains 77% of DM as starch, corn and sorghum contain 72%, and barley and oats contain 57 to 58%. In vitro systems have provided valuable data on kinetic aspects of starch digestion. Molecular biological techniques have provided a clearer picture of the ruminal microbial milieu. Proportions of starch fermented in the rumen can be predicted satisfactorily for a variety of grains and processing methods. Compared with dry rolling, steam processing (flaking or rolling) increases ruminal digestibility of starch (percentage of intake) from 52 to 78% for sorghum, from 75 to 85% for corn, and six percentage units or less for other grains. Recent research provides new insight into pancreatic function and intestinal glucose transport systems. The capacity to digest starch in the intestine ranges from 45 to 85% of starch entering the duodenum, with that capacity apparently limited by the supply of pancreatic amylase. There is evidence that amylase secretion may be enhanced by increasing duodenal entry of protein. Capacity for active transport of glucose across of gut wall does not seem to limit the amount of starch digested that is absorbed as glucose. For ruminants eating medium- to high-concentrate diets, about 30% of their total glucose need comes from glucose absorption, 50% from organic acid absorption (substrates for hepatic gluconeogenesis), and 20% from other sources. When glucose absorption from the gut increases, ruminants generally adjust (decrease) gluconeogenesis to meet their need; that need is directly linked to DE intake. In terms of overall ME yield, grain starch is best used when it is fermented in the rumen. However, close coordination of protein and starch supply to the duodenum may improve capture of starch in the form of glucose.

Starch utilization by ruminants: from basics to the bunk.

1. Chemical, Protein Precipitation and Bioassays for Tannins, Tannin Levels and Activity in Unconventional Feeds, and Efects and Fate of Tannins.- 2. Treatment of Plant Material, Extraction of Tannins, and an Overview of Tannin Assays Presented in the Manual.- 3. Measurement of Total Phenolics and Tannins Using Folin-Ciocalteu Method.- 4. Determination of Condensed Tannins (Proanthocyanidins).- 5. Gallotannin Determination by Rhodanine Assay.- 6. Gallotannin Determination Using HPLC.- 7. Determination of Hydrolysable Tannins (Gallotannins and Ellagitannins) after Reaction with Potassium Iodate.- 8. Determination of Protein-Precipitable Phenolics.- 9. Protein-Binding Capacity by Filter Paper Assay.- 10. Radial Diffusion Assay.- 11. Tannin Bioassay.- 12. Radiolabelled BSA Precipitation Method.- 13. Simplified Radiolabelled BSA Precipitation Method.- 14. Characterization of Phenolic Compounds by Thin Layer Chromatography (TLC).- 15. References.- 16. A Summary of Results from the First Phase of the Coordinated Research Project.- 17. List of Participants in the Co-Ordinated Research Project.

Quantification of Tannins in Tree and Shrub Foliage: A Laboratory Manual

Influence of hydrogen on rumen methane formation and fermentation balances through microbial growth kinetics and fermentation thermodynamics

Direct microscopic examination of the rumen and its contents shows microbial populations largely attached to feed particles in the digesta Most feeds contain a surface layer that is resistant to attachment and therefore to digestion Infiltration of these recalcitrant epidermal layers through damage sites or through focused enzymatic attack is essential for initiation of the digestive process Proliferation of primary colonizing cells produces glycocalyx-enclosed microcolonies Secondary colonizers from the ruminal fluid associate with microcolonies, resulting in the formation of multispecies microbial biofilms These metabolically related organisms associate with their preferred substrates and produce the myriad of enzymes necessary for the digestion of chemically and structurally complex plant tissues Upon accessing the internal, enzyme-susceptible tissues, microbial "digestive consortia" attach to a variety of nutrients, including protein, cellulose, and starch and digest insoluble feed materials from the inside out Substances that prevent microbial attachment or promote detachment (eg, condensed tannins, methylcellulose) can completely inhibit cellulose digestion As the microbial consortium matures and adapts to a particular type of feed, it becomes inherently stable and its participant microorganisms are notoriously difficult to manipulate due to the impenetrable nature of biofilms Properties of feed that place constraints on microbial attachment and biofilm formation can have a profound effect on both the rate and extent of feed digestion in the rumen Developments in feed processing (ie, chemical and physical), plant breeding, and genetic engineering (both of ruminal microorganisms and plants) that overcome these constraints through the promotion of microbial attachment and biofilm formation could substantially benefit ruminant production

K J Cheng

Papers

Microbial attachment and feed digestion in the rumen.