VPB 121: Veterinary Physiology - II (2+1)

RUMEN FERMENTATION

• The unique feature of digestive physiology in the ruminants is the fermentative digestion  known as microbial digestion which occurs  in the rumen and reticulum. Microbial digestion of food also occurs in the three chambered ruminats, camel, lama and in the stomach of marsupials and in hippopotamus.
• Anaerobic ciliate protozoa and non-spore forming anaerobic bacteria and anaerobic fungi are the major microbes in rumen.Some facultative bacteria are also present. The microbes have a volume of 3.6 % of strained rumen liquor of which 50% is contributed by cilitate protozoa and the remaining 50% by the bacteria.The number of rumen fungi is negligible but their activity is of great importance.
• The bacteria and protozoa grow on the substrates of the food in the fore stomach of the ruminants.

Establishment of bacteria in young ruminants

• Development of bacterial flora in young ruminants occurs at a very early age.
• The nature and rate of development is affected by type of diet fed and degree of isolation of young from adult animals. Under normal conditions, bacteria of adult type establish at about 6^th week of age in young animals.
• The ciliates may not become established in young animals unless they are maintained in close contact with animals harbouring them or are inoculated.
• Rumen microbes digest all major carbohydrates of ruminant diet such as cellulose, hemicellulose, pectin and xylose etc. These group of carbohydrates are not digested by mammalian digestive enzymes. The fermentation of cellulose is a slower process and is incomplete in rumen, but the digestion of cellulose and hemi-cellulose is almost completed in the rumen.
• Microbes derive their energy for their growth by fermenting cellulose, hemicellulose, pectin, soluble sugars, starch, the carbohydrates of major plant constituents .
• Rumen microbes are responsible for the digestibility of about 70 to 85% dry matter of the diet in ruminants, results in the production of volatile fatty acids (Acetic, Butyric and propionic acids) gases like CO₂, methane (CH₄) , ammonia (NH₃)with small amounts of N₂, H₂, and O₂ and microbial cells.
• From carbohydrates, certain organic isoacids, NH₃ and minerals, the microorganisms can synthesise good quality microbial proteins and    B complex vitamins required for their growth and metabolic activities.
• They also hydrolyses lipids, unsaturated fatty acids. Proteins and NPN substances of dietary and salivary sources get degraded by the microbes and the released amino acids, NH₃ are utilized for microbial growth and microbial protein synthesis. Thus the ruminant animal can be maintained on diets free of essential amino acids.
• In animals maintained in green pasture, the number of bacteria is higher than those fed dry rations. When ciliate protozoa are absent, viable bacterial count increases. Rate and method of feeding also affects bacterial count.
• The pH of the rumen liquid ranges from 5.8 to 7.0, which get decreased after feeding.

Rumen as microbial habitat

• Maintenance of constant temperature of 40⁰C
• Maintenance of constant pH of 6 – 7 by the HCO₃ & HPO₄ buffers of saliva
• Aqueous environment by continuous salivary secretion
• Continuous supply of substrates for microbial activity
• Mixing of the ruminal contents by rumino-reticular contractions
• Continuous removal of the fermentative end products.
• Abomasal secretions are dependent on volume of material flowing into it and pyloric distension. A rise in abomasal pH, short chain fatty acid level stimulate HCl and gastrin secretion. Parasympathetic nerves and gastrin also involved in abomasal secretion.
• Microbes derive their energy for their growth by fermenting cellulose, hemicellulose, pectin, soluble sugars, starch, the carbohydrates of major plant constituents .They result in the production of acetic, butyric propionic and lactic acids and gases like CO₂, methane and H₂.
• Abomasum receives a continuous flow of these materials and functions as a true stomach by secreting gastric juice. More of gastric secretion is from the fundic glands but the pyloric secretion is low. Gastric juice in the fundus region contain pepsin and HCl, has a pH close to 1.0. Pyloric secretions are slightly alkaline with little peptic activity.