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

FERMENTATION OF CARBOHYDRATES

• Speed of  carbohydrate fermentation varies with their availability and solubility. 
• Soluble sugars are rapidly fermented but starch is less rapidly fermented.
• Cellulose and hemi-cellulose are slowly fermented.
• Starch is a glucose polymer with alpha 1, 4 glucose linkage.
• The fructosans are polymer of fructose units with beta linkage.
• In roughages, most of the  carbohydrates are structural and found in plant cell wall (cellulose, hemicellulose and pectin).
• Cellulose is beta 1,4 glucose linkage polysaccharide and hemicellulose is polysaccharide composed of beta linked xylose units and few hexoses.
• Pectin, found in cell wall and intracellular is beta linked galacturonan (polysaccharide based on galactose with uronic acid).
• The alpha linkage can be  readily hydrolysed  by amylases, whereas the beta linkage can be digested only by microbial enzymes, but not by mammalian enzymes. 
• Lignin, a phenolic compound, a constituent of plant cellwall is resistant even to microbial enzymatic digestion. Only a small portion of dietary lignin is digestible due to the action of rumen fungi.
• The lignin reduces the digestibility of cell wall  carbohydrates.
• Lignin and cellulose content increase with the age of the plant and temperature.  
• Fructosans are more in young grasses. 
• Xylose is the most abundant sugar in grasses.