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

PRINCIPLES OF FERMENTATION IN SILO

The fermentation in silo can be regulated by Encouraging lactic acid formation by bacteria present on the fresh herbage or Addition of preservatives such as sodium matabisulphite or by direct addition of a weak acid solution. The first method the soluble carbohydrates present in the plant material is fermented to lactic acid, resulting in a lowering of pH to within the range of 3.8 – 4.2. Material of this type has a lactic acid content (8-12% drymatter) and is described as ‘well preserved silage’. As long as the silage mass is kept under anaerobic conditions, its pH will remain stable at 4 and the silage can be stored for 3-4 years. If, however, rain is allowed to enter the silage (or) if lactic acid concentration is scarce, secondary clostridial fermentation take place. There are two types clostridias, while one group cause a break down of the lactic acid with the production of butyric acid, the other group of clostridia attack amino acids, with the formation of ammonia, organic acids, amines and CO2. Either or both of these types of clostridia may become dominant in poorly preserved silage which will have a comparatively high pH value of above 5.

In well preserved silage pH 3.8 –4.2

The process of fermentation can be divided into four phases: Phase I: Aerobic phase, plant enzymes breaks down soluble carbohydrates to carbon dioxide and water. Phase II: Enterobactor species of bacteria acts on soluble carbohydrates producing acetic acid and lowers the pH slightly. Phase III: Lactic acid producing bacteria (Lactobacillus and Streptococcus spp) ferments soluble carbohydrates present in the plant material to lactic acid resulting in a lowering of pH . Phase IV: Lactic acid production peaks; stabilises to within the range of 3.8 – 4.2. At this pH, crop preservation is good. The second method of silage making process involves the sterilisation of the mass in the silo by adding chemical sterilisation agents such as formaldehyde, sulphur dioxide or sodium metabisulphate. The success of this method depends mainly upon ensuring ample mixing with the crop, which may frequently be difficult to carry out. The nutritive value of the preserved material should be very similar to that of the original herbage, if effluent production is not great and satisfactory sterilisation is achieved. Direct acidification of the crop, is yet an another method of preserving herbage; one such system is the A.I.V. process, named after originator A.I.Virtanen. The mixture of acids used in this process consists of hydrochloric acid and sulphuric acid. These acids are added to material during ensiling in sufficient quanity to lower the pH value below 4. A.I.V. silage has been shown to be palatable and harmless to ruminants.

Four phases in silage: Soluble carbohydrate converted to CO2; H2O. Enterobactor produces acetic acids; lowers pH. Lactic acid producing bacteria produce lactic acid; further lower pH. pH stabilizes at 3.8 – 4.2. silage well preserved. Chemical sterilization by formaldehyde/ suplhur dioxide or sodiummetabisulphate Direct acidification: A.I.Virtanen – acid mixture added to lower pH to 4.0