Table 1 Comparison of the rumen with the human colon—characteristics and properties of fermentative digestion in these gut compartments that specialize in fermentative digestion
From: Hydrogen and formate production and utilisation in the rumen and the human colon
Characteristic | Rumen | Human colon |
|---|---|---|
Mode of digestion | Pregastric—foregut fermentor | Postgastric—hindgut fermentor |
| Â | Continuously stirred/mixed tank reactor | Plug flow tubular system |
Diet | Evolved for efficient fibre degradation and utilisation. Major metabolizable energy supply (~ 70%) of the host energy requirements | Adapted to hydrolysing and fermenting undigested dietary residues and host endogenous secretions. Minor contribution to host energy requirements |
| Â | Breakdown dietary protein and non-protein nitrogen for synthesis of microbial protein | Post absorptive compartment |
| Â | Synthesis of B vitamins | Post absorptive compartment |
| Â | Rumen system evolved for detoxification/biotransformation of phytotoxins and mycotoxins | Host system evolved for transport and excretion of toxic/xenobiotic compounds |
Blood glucose | Low—rely on gluconeogenesis to generate glucose precursors | High |
Microbiology | Anaerobic bacteria and methanogenic archaea | Anaerobic bacteria and methanogenic archaea |
| Â | Ciliate rumen protozoa | Flagellate protozoa? |
| Â | Anaerobic rumen fungi | Â |
| Â | Bacteriophage | Bacteriophage |
VFA/SCFA | Acetate, propionate and butyrate are the predominant volatile fatty acids | Similar molar proportions of the three main volatile fatty acids |
| Â | Branched chain VFAs | Similar |
|  | Lactate → Propionate | Similar turnover |
|  | Succinate → Propionate | Similar turnover |
Gas composition | CO2 65%; CH4 27%; N2 7%; O2 0.6%; H2 0.2% | CO2 10%; CH4 14%; N2 65%; O2 2.3%; H2 3% |
|  | CO2 produced from fermentation and HCO3− in saliva. N2 and O2 is ingested with feed and diffuses through the rumen wall. Partial pressure of H2 maintained at a very low level. CH4 emission amounts to 2–12% of gross energy | N2, and O2 ingested, with CO2, H2 and CH4 resulting from colonic fermentation. Less CO2 and CH4 than the rumen but with higher H2 concentrations |
Gas elimination | Mainly eructation | Flatus and reabsorption and removal by lungs |