Role of microorganisms in ensilage

In fresh herbage, 75-90 per cent of the total nitrogen is present as protein. After harvesting, rapid proteolysis (hydrolysis of peptide bonds) occurs and, after a few days of wilting in the field, the protein content may be reduced by as much as 50 per cent. The extent of protein degradation varies with plant species, DM content and temperature. Once the material is ensiled, proteolysis continues but the activity declines as the pH falls. The products of proteolysis are amino acids and peptides of varying chain length. 

Further breakdown of amino acids occurs as a result of plant enzyme action, although this is considered to be limited. Most destruction of amino acids in silage is brought about by microbial activity rather than by plant enzymes. 

Aerobic fungi and bacteria are the dominant microorganisms on fresh herbage, but as anaerobic conditions develop in the silo they are replaced by bacteria able to grow in the absence of oxygen. These include lactic add bacteria, clostridia and enterobacteria. 

Clostridia grow best at pH 7.0-7.4. They cannot tolerate acid conditions, and a pH of 4.2 is usually considered to be low enough to inhibit their growth. The nature of the acids responsible for lowering the pH is important, with undissociated organic acids being the most potent. Clostridia are particularly sensitive to water availability and require very wet conditions for active growth. Mth very wet crops (i.e. those 

Glucose 2 lactic add Fructose 2 lactic add Pentose lactic acid + acetic acid Heterofermentative 

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