Silage Fermentation and Preservation
Dr.Khalid Pervaiz ,,DVM ; M.phil (UVAS)
Quality silage is achieved when lactic acid is the predominant acid produced, as it is the most efficient
fermentation acid and will drop the pH of the silage the fastest. The faster the fermentation is completed, the
compromise between reducing labor requirements and field losses versus losses in the fermentation process
that will eventually preserve the crop. Ideal fermentation is dependent upon decisions and management
practices implemented before and during the ensiling process. The primary management factors that are
under the control of the producer are:
1. Stage of maturity of the forage at harvest.
2. The type of
fermentation that occurs in the silo or bunker. 3. Type of storage structure used and methods of harvesting
During the ensiling process, some bacteria are able to break down cellulose and hemicellulose to various simple sugars. Other bacteria break down simple sugars to smaller end products (acetic, lactic and butyric acids). The most desirable end products are acetic and lactic acid. As the bacteria degrade starches and sugars to acidic and lactic acids, dry matter is lost. Attention to details such as speed of harvesting, moisture content, length of chop, silage distribution and compaction can greatly influence the fermentation process and storage losses.
Efficient fermentation ensures a more palatable and digestible feed, which encourages optimal dry matter intake that translates into improved animal performance. Making consistent, high-quality silage requires sound management decisions and attention to details. It is important that bacteria responsible for production of acetic and lactic acid grow and multiply immediately after storing in the Bunker Proper packing of the chopped fodder to voiding of air (oxygen) provides the environment needed by bacteria to break down fiber components and sugars.
Oxygen must be removed from the chopped forage by pressing by tractor layer by layer of forage to maximize reproduction of acetic and lactic acid-producing bacteria. Microbes (bacteria) responsible for fermentation need anaerobic (in the absence of air) conditions. As bacteria consume sugars, end products produced (acetic and lactic acid) cause the pH to drop and at 4pH all bacterial activities ceased and fermentation process stop. Quality silage is achieved when lactic acid is the predominant acid produced, as it is the most efficient fermentation acid and will drop the pH of the silage the fastest. The faster the fermentation is completed, the more nutrients will be retained in the silage so some fermentation baceria and Enzyme (Sil- All) All-tech@ may be used for improved Quality of Silage A critical time is ensiling after the initial three to five days and and after 30 days to complete the process .
There is a gradual increase in lactic acid as lactic acid-producing bacteria break down simple sugars. The pH drops to between 3.8 to 4.2. At such acidic conditions, further bacterial action is topped. If the forage is too dry, fermentation is restricted and the pH cannot drop sufficiently. If Silage due to dry or more moisture level in fodder does not drop pH to about 4 spoilage will occur due to butyric acid production
The following six phases describe what occurs during ensiling, storage and feed-out of fermented forages: Phase I As the forage is harvested, aerobic organisms predominate on the forage surface. During the initial ensiling process, the freshly cut plant material, and more importantly the aerobic bacteria, continue to respire within the silo structure.
The oxygen utilized in the respiration processes is contained within and between the forage particles at the time of ensiling. This phase is undesirable since the aerobic bacteria consume soluble carbohydrates that might otherwise be available for the beneficial lactic acid bacteria or the animal consuming the forage. Although this phase reduces the oxygen to create the desired anaerobic conditions, the respiration process produces water and heat in the silage mass. Excessive heat build-up resulting from an extended Phase I period can greatly reduce the digestibility of nutrients such as proteins. Another important chemical change that occurs during this early phase is the breakdown of plant proteins. Proteins are first reduced to amino acids and then to ammonia and amines. Up to 50 percent of the total plant protein may be broken down during this process. The extent of protein breakdown (proteolysis) is dependent on the rate of pH decline in the silage. The acid environment of the silage eventually reduces the activity of the enzymes that break down proteins. Phase I ends once the oxygen has been eliminated from the silage mass. Under ideal crop and storage conditions, this phase will last only a few hours.
With improper management, this phase could continue for several weeks. The primary objective at ensiling time is to manage the crop so air infiltration is minimized; thereby shortening the time required to achieve an anaerobic environment. Key management practices are proper maturity, moisture, chop length and rapid filling with adequate packing and proper sealing of the storage structure. Phase II After the oxygen in the ensiled forage has been utilized by the aerobic bacteria, Phase II begins. This is an anaerobic fermentation where the growth and development of acetic acid-producing bacteria occurs. These bacteria ferment soluble carbohydrates and produce acetic acid as an end product. Acetic acid production is desirable as it can be utilized by ruminants in addition to initiating the pH drop necessary to set up the following fermentation phases. As the pH of the ensiled mass falls below 5.0, the acetic bacteria decline in numbers as this pH level inhibits their growth. This signals the end of Phase II. In forage fermentation, Phase II lasts no longer than 24 to 72 hours. Phase III The increasing acid inhibits acetic bacteria and brings Phase II to an end.
The lower pH enhances the growth and development of another anaerobic group of bacteria, those producing lactic acid. Phase IV This is a continuation of Phase III as the lactic-acid bacteria begin to increase, ferment soluble carbohydrates and produce lactic acid. Lactic acid is the most desirable of the fermentation acids and for efficient preservation, should comprise greater than 60 percent of the total silage organic acids produced. When silage is consumed, lactic acid will also be utilized by cattle as an energy source. Phase IV is the longest phase in the ensiling process as it continues until the pH of the forage is sufficiently low enough to inhibit the growth of all bacteria. When this pH is reached, the forage is in a preserved state. No further destructive processes will occur as long as oxygen is kept from the silage. Phase V The final pH of the ensiled forage depends largely on the type of forage being ensiled and the condition at the time of ensiling. Haylage should reach a final pH of around 4.5 and corn silage near 4.0. The pH of the forage alone is not a good indicator of the quality of the silage or the type of fermentation that occurred. Forages ensiled at moisture levels greater than 70 percent may undergo a different version of Phase IV. Instead of lactic acid producing bacteria developing, large populations of clostridia bacteria may grow in the silage.
These anaerobic bacteria produce butyric acid rather than lactic acid, which results in sour silage. With this type of fermentation, the pH may be 5.0 or above. Phase VI This phase refers to the silage as it is being fed out from the storage structure. This phase is important because research shows that nearly 50 percent of the silage dry matter losses occur from secondary aerobic decomposition. Phase VI occurs on any surface of the silage that is exposed to oxygen while in storage and in the feedbunk. High populations of yeast and mold or the mishandling of stressed crops can lead to significant losses due to aerobic deterioration of the silage. Proper management is vital to reduce these losses and improve the bunk life