ANN 111: Principles of Animal Nutrition and Feed Technology (2+1)

FACTORS AFFECTING THE NUTRITIVE VALUE OF SILAGE

Chemical changes: Plant enzymes: Plant continues to respire as long as oxygen present or until the plant sugars are used up.  Sugars are oxidised to carbon dioxide and water, with the production of heat causing rise in temperature of the mass. In addition, proteolysis also occurs immediately after the herbage is cut.  Protein is rapidly broken down to simpler substances mainly amino acids. Packing the silo compactly eliminates air pockets and prevents this activity. However, if the herbage is not well consolidated, then air may penetrate into the mass and the temperature will continue to rise. Thus over heated product will be dark brown or black in colour with low feeding value due to excessive loss of soluble carbohydrate and a lowering of the protein digestability.	Sugars   (O) CO2 + H2O. Protein to Amino acids.
Microorganisms: In anaerobic condition, the microbes present on the plant surface multiply, using the contents of a cell as medium to produce lactic acid. Thus the acidity of the mass drops to about pH  4.0 – 4.2 and at this pH, organisms other than the lactic acid bacteria are inhibited as long as conditions remain anaerobic. These lactic acid bacteria are classified into 2 main groups, the homofermentative lactic acid bacteria and the heterofermentative lactic acid bacteria. Homofermentative lactic acid bacteria are more efficient at converting hexose into the acid than the heterofermentative organisms. During ensilage about 60% of the proteins are broken down to amino acids even in well preserved material. Nutritive value - wise break down to amino acids is not  a drawback, but in badly preserved material the amino acids are broken down further to produce various amines such as tryptamine, phenyl ethylamine and histamine that could be toxic to animals if absorbed into the blood. Though mineral compounds present in herbage such as potassium, calcium, sodium and magnesium may form salts of lactic acid and volatile acids,  their bio availability is not impaired in silage making.	Production of lactic acid lowers pH to 4.0. 60% protein broken down to amino acids. No other organism can survive at this pH. In badly preserved silage amino acids are further broken down to toxic amines.