Rumen Microorganisms and functions
Rumen Bacteria
| 1. Cellulolytic Species | Fibrobacter succinogenesRuminococcus albus & R. flavifaciensButyrivibrio fibrisolvens |
| 2 Hemicellulolytic Species | Butyrivibrio fibrisolvensRuminococcus sp. &Bacteroides ruminicola |
| 3. Pectinolytic Species | Butyrivibrio fibrisolvensBacteroides ruminicolaSuccinivibrio dextrinosolvens |
| 4. Amylolytic Species | Bacteroides amylophilusStreptococcus bovisSuccinomonas amylolytica |
| 5. Ureolytic Species | Succinivibrio dextrisolvensSelenomonas sp.Butyrivibrio spBacteroides ruminicola |
| 6. Methane producingSpecies | Methanobrevibacter ruminantiumMethanobacterium formicicumMethanomicrobium mobile |
| 7. Sugar-Utilising Species | Treponema bryantiLactobacillus sp. |
| 8. Acid-Utilising Species | Megasphera elsdeniiSelenomonas ruminantium |
| 9. Proteolytic Species | Bacteroides amylophilusB. ruminicolaButyrivibrio fibrisolvensStreptococcus bovis |
| 10. Ammonia Producing Species | Bacteroides ruminicolaMegasphera elsdenii |
| 11. Lipid-Utilising Species | Anaerovibrio lipolyticaButyrivibrio fibrisolvensMicrococcus sp. |
Rumen protozoa
Many species of protozoa are active in rumen. All protozoa are strictly anaerobes and found only in ruminants.
Ciliates form the bulk of protozoa and flagellates are present to a very limited extent. The ciliates belong to two families as shown in diagram below-
Many species of micro-organisms are present in the rumen and variations occur in number of certain species with time after feeding, dietary regime and individual differences. Protozoal number is affected by pH (<5.5), type and composition of diet, season and frequency of feeding. Highly digestible diets increase their number.
Protozoa store large quantities of reserve starch, which is used when exogenous energy supply is exhausted. Some facultative bacteria are also present.
The microbes have a volume of 3.6% of strained rumen fluid and this volume contains 50% ciliate protozoa and 50% bacteria.
Metabolic activity of bacteria is far greater than protozoa though total volume of small bacteria might be same as ciliate protozoa, which is due to greater surface area provided by the bacteria.
Protozoal number range between 105 and 106 per ml fluid. Most of the rumen bacteria and protozoa are strict anaerobes.
Role of protozoa
Protozoa increase in digestibility and weight gain is observed in faunated animal than in defaunated animals. But the absence of protozoa does not affect the animal performance.
The protozoa help to stabilise the rumen fermentation, by ingesting feed particles and storing reserve polysaccharides and they may control the availability of substrates by sustaining uniform fermentation between feedings.
Mixed protozoal-bacterial protein is better in quality than bacterial protein alone in contributing essential nutrients to ruminant animal.
Rumen fungi
Anaerobic fungal zoospores are found in rumen. Several are flagellate organisms. Neocallimastix frontalis, Sphaeromonas communis and Piromonas communis are identified in rumen. Presence of plant cellwall carbohydrates facilitate increase inthe fungal population (Spores) and thus further help in lignocellulosic digestion.
The fungi are important in the digestion of plant cell wall, their number ranges from 105 to 107 per gram of rumen contents. Feeding of high roughage diet increases their number.
Fungi play a significant role in adhesion with plant cell wall. It is difficult to culture fungi in-vitro as they are strict anaerobes.
Functions of rumen micro-organisms
- Ferment the dietary carbohydrates including the cell wall constituents of plants, which can not be enzymatically digested by the mammals.
- Produces short chain fatty acids like acetic, butyric, propionic and lactic acids and gases such as CO2, Methane, and H2.
- The short chain fatty acids are absorbed from the rumen and are the major energy source of the ruminants.
- By microbial enzymes the dietary proteins are broken down in to ammonia and branched-chain VFAs.
- The short chain fatty acids and NH3 are utilised for growth of microbes and microbial protein synthesis.
- The microbial proteins are utilised by the host animal as a source of quality protein.
- Triglycerides are hydrolysed to glycerol and fatty acids. The glycerol is converted to propionic acid. The unsaturated fatty acids are hydrogenated .
- Microbes synthesize vitamin K and B complex vitamins.