VPB 321: Animal Biotechnology (2+1)

ORGANISMS

• Fermentative digestion of forages occurs in ruminants in the well developed fore stomach (the reticulo-rumen). This organ is maintained in a relatively stable continuous anaerobic culture of mixed population of protozoa, bacteria, fungi and bacteriophage.
• The rumen fluid pH is maintained at close to neutrality by continuous saliva which balances the production of acidic end products of fermentation.
• The short chain fatty acids are either absorbed directly or pass out of the rumen in the digesta to the intestines where they are absorbed.
• The anaerobic bacteria are the major organisms in the rumen which help in fibre digestion by attached to and attack damaged parts of plants and digestion occurs from outside towards the centre.
• The fungi are mostly fibrolytic with the major substrates being cellulose and hemicellulose. Their major role may be weakening of feed particle structure as most species have radii which penetrate plant tissues and therefore tend to digest plant materials from inside.
• Prevotella ruminicola (formerly Bacteroides ruminicola) is one of the most numerous groups of rumen bacteria and is found in ruminants fed on many different diets. These are strictly anaerobic and involved in the degradation and utilization of starch and of plant cell polysaccharides such as xylans and pectins. These bacteria are also believed to play an important role in the degradation of proteins and in the uptake and fermentation of peptides.
• Ruminobacter amylophillus accounts for about 15% of isolates from rumen and involved in starch degradation. They also possess significant proteolytic activity.
• Fibrobacter succinogenes is one of the most widespread cellulolytic bacteria of the rumen. This accounted for around 20% of the isolates recovered from a cow fed wheat straw; in cows fed other diets, F. succinogenes accounted for about 5% of the isolates. Succinivibrio dextrinosolvens ferments dextrins in animals fed starch. In addition to their capacity to digest starch, some strains also possess enzyme which could enable products of plant cell wall breakdown to be used.
• Anaerovibrio lipolytica has two key properties that probably reflect its ecological roles, the hydrolysis of lipids and utilization of lactate. Ruminococcus flavefaciens and R. albus are involved in plant fibre degradation in the rumen.