Applications of Biotechnological Processes Silage Production

Cattle and sheep are dependant upon grass for food. During winter, farmers need to provide an alternative food source. In the past, livestock were fed hay (dried grass), but this has a low nutritional value. Today, cattle are fed grass which has been fermented (silage), as it retains it nutritional value.

Silage is light brown- yellow in colour, has little smell and can be kept stable for many years.

Procedure Silage is made through the fermentation of grass. The process is called ensilage. Grass is cut and allowed to wilt for several hours.

It is then transferred into “silos” or black polythene bags/bales. Anaerobic conditions are generated in the sealed silo (any oxygen is used up by respiring, cut grass).

A cocktail of bacterial species and hydrolytic enzymes are added e.g. pectinases and cellulases Cellulases and pectinases digest the grass cell walls to release nutrients from the cells that bacteria can utilise

A mixture of bacteria are used as no single species is suited to the conditions that occur throughout the fermentation process. Lactobacillus and Enterococcus species are usually used.

Enterococcus requires aerobic conditions and a higher pH to work, so it is better suited to the early stages of fermentation. Through the metabolic activity of Enterococcus, conditions in the silo/plastic bag will become more acidic (< pH5) and anaerobic. In these conditions the Lactobacillus will take over the fermentation process

The temperature also rises from around 5 o C to 50 o C due to the microbial activity. The rise in temperature further aids the fermentation process.

Spoilage Spoilage microorganisms e.g. Clostridium and Enterobacillus, could potentially reduce the quality of the silage, making it unpalatable to livestock. However, the acidic and anaerobic conditions created through the fermentation process inhibit the action of these microbes.

Past Paper Questions 2006 Q Q1(i)