The Physiological Functions of the Reticulorumen Maintain an Environment Favorable to Fermentation Patterns That Are Beneficial to the Host
The host animal has no direct control over the metabolism of the microbes in its gut. However, important physiological factors influence the gastrointestinal (GI) fermentation process.
For the host to ensure that the proper type of fermentation patterns occur, it must maintain within the rumen (or colon) conditions that promote the growth and favorable metabolic patterns of the most beneficial bacteria and other microbes. The following requirements must be met by the host for proper fermentation to occur:1. Substrate for fermentation must be supplied.
2. Temperature must be maintained at or near 37o C.
3. Ionic strength (osmolality) of the rumen fluid must be kept within an optimal range (near 300 mθsm).
4. A negative oxidation-reduction potential must be maintained (-250 to -450 mV).
5. Indigestible waste (solid material) must be removed.
6. The rate of removal of microbes must be compatible with the regeneration times of the most favorable microbes.
7. Acid products of anaerobic fermentation (VFAs) must be buffered or removed.
The first of these requisites, delivery of substrate, requires only eating; others (e.g., temperature, ionic strength) are met by the same homeostatic mechanisms that maintain these physiological conditions within the host body in general. Maintenance of an appropriate oxidation-reduction potential requires only that oxygen be kept away from the fermentation site. The remaining requisites for fermentation, however, have necessitated the development of special physiological functions associated with the forestomach (or hindgut). These specialized functions include the motility patterns characteristic of the reticulorumen, the direct absorption of VFA, and the production of copious amounts of saliva.