Silage

MAKING OF SILAGE

(Preservation of Green Forage Crop)

Silage is the feedstuff resulting from the preservation of green forage crops by acidification. The first phase is the aerobic phase, which occurs in the presence of oxygen (air). The oxygen that is present in the forage, as it is placed into storage, is consumed by the plant material through the process of respiration. Under aerobic conditions, plant enzymes and microorganisms consume oxygen and burn up plant water-soluble carbohydrates (sugars), producing carbon dioxide and heat. The first phase should be as brief as possible to maintain the quality of the silage. Excessive aerobic fermentation reduces the energy content of the silage and may cause heat damage to proteins.

The second anaerobic phase begins when available oxygen is used up by respiration and aerobic bacteria cease to function. Anaerobic bacteria begin to multiply and the fermentation process begins. The lactobacilli produce lactic acid from the fermented plant material which lowers the pH of the silage. Fermentation completely ceases after three to four weeks when the pH becomes so low that all microbial growth is inhibited.

The ensiling and storage system's main functions are to exclude air during the ensiling process and to prevent air from entering the silage during storage.
Limiting air present in the silage will enhance feed quality and reduce spoilage.

SILO TYPES

Horizontal Silos

There are two types of horizontal silos - below ground level (i.e., pit or trench) and above ground (i.e. bunker and stack). The main advantage of horizontal silos is their low capital cost and suitability to feeding livestock in widely separated pens.

Trench silos
Are usually dug into a slope with the "downhill" end open for drainage and access.

Bunker silos
are used in flat areas unsuitable for trench silos. Above-ground walls are constructed using concrete, earth or wood and braced with timbers or concrete buttresses.
 
The correct height and width to make a silo depends on daily silage usage based on the removal of a minimum of 10 cm (4 in.) per day from the silage face. Removing less silage leads to spoilage or freezing problems. The silo should be as high as possible to minimize silo width, thereby minimizing surface spoilage. Increased silage height aids in packing.

•    Silo Length depends on the totalsilage needed annually.

•    Capacities are dependent on average densities of silage. Silage density increases with increasing moisture content, shorter cut length packed silage depth and amount of packing.


 
DETERMINING MOISTURE CONTENT OF FORAGE
a) Using a Microwave Oven

1.  Cut a representative cross-section of forage from the windrow.
2.  Cut into 0.6 cm (1/4 in.) pieces.
3.  Weigh 100 grams of material and place on a paper plate or bag.
4.  Spread sample out evenly and place in microwave over on high heat for three to
     four minutes.
5. Weigh sample and record weight.
6. Stir sample and place in microwave oven on high heat for one minute. Reweigh
and record weight.
7. Repeat step six until weight loss is less than one gram. This is the dry weight.

Calculation: wet wt. grams - dry wt. grams /100 = percent moisture
 
 b) by Hand Method

Forage squeezed in hand    Moisture %
Water easily squeezed out and material holds shape    80+
Water can just be squeezed out and material holds shape    75-80
Little or no water can be squeezed out but material holds shape    70-75
No water can be squeezed out and material falls apart slowly    60-70
No water can be squeezed out and material falls apart rapidly    60 or less
    
Maize crop

SILAGE ADDITIVES

There are three categories of Silage additives 
I.    Stimulants of fermentation (microbial inoculants, enzymes, fermentable substrates),
II.    Inhibitors of fermentation (acids, other preservatives), and
III.    Nutrient additives (ammonia and urea).


STIMULANTS OF FERMENTATION

a)    LAB:   Natural populations of lactic acid bacteria (LAB) on plant material are often low in number and heterofermentative . The concept of adding a microbial inoculant to silage was to add fast growing homofermentative lactic acid bacteria (hoLAB) in order to dominate the fermentation resulting in a higher quality silage. The organism(s) from microbial inoculants must be present in sufficient numbers to effectively dominate the fermentation. Thus the most commonly recommended inoculation rate supplies 100,000 (or 1 x 105) organisms per gm of wet forage. Most microbial inoculants are available in powder or granular form. Use a metered liquid sprayer to evenly disperse the inoculant on the forage. Unused liquids should be discarded after a period of 24 to 48 h because bacterial numbers begin to decline. Application to forage at the chopper is highly recommended in order to maximize the time that microorganisms have in contact with fermentable substrates. Inoculants applied in a liquid may be more advantageous since bacteria are added with their own moisture to help speed up fermentation. Storage is an important aspect of a high quality inoculant that contains live microorganisms. Inoculants should be kept in cool dry areas away from direct sunlight. Moisture, oxygen and sunlight will decrease stability of inoculants. Opened bags of inoculants should be used as soon as possible.

Recently, Lactobacillus buchneri, a heterolactic bacteria capable of producing lactic and acetic acid, has been included as an inoculant for improving the aerobic stability of silages.  Aerobic stability was markedly enhanced and improved with increasing inoculation rate.

b)    ENZYME ADDITIVES: A variety of enzymes, particularly those that digest plant fiber and starch have used as silages additives. Silage additives may contain single enzyme complexes, combinations of enzyme complexes and combinations of enzyme complexes and LAB. Plant fiber-digesting enzymes (cellulases and hemicellulases) are the most widely used enzyme additives.

There are two primary reasons for adding fiber-digesting enzymes to silage. First these enzymes could partially digest the plant cell walls (cellulose and hemicellulose) yielding soluble sugars which could be fermented by LAB to lower the silage pH. This would stimulate silage fermentation and improve fermentation quality by increasing the rate and extent of decline in pH, increasing the concentration of lactic acid, improving the lactic acid:acetic acid ratio (which is indicative of greater efficiency of fermentation), and hence reduce DM losses. A faster decline in pH would also limit degradation and deamination of forage proteins and reduce ammonia production. Second, partial digestion of the plant cell wall may improve the rate and/or extent of digestibility. In order for the first event to take place the rate of cellulose hydrolysis must coincide.
 
MOLASSES. Molasses has been used as a fermentation stimulant. Molasses is a by-product of the sugar-cane and sugar-beet industries and contains 79% soluble carbohydrates; 45 to 50%, of which sucrose is the main component. Molasses provides a relatively cheap source of fermentable carbohydrate for lactic acid bacteria and has been applied at a rate of 40-80 lb per ton of fresh forage.

INHIBITORS OF FERMENTATION

PROPIONIC ACID: propionic acid has the greatest antimycotic activity. The antimycotic effect of propionic acid is enhanced as pH declines, making it an ideal candidate for improving the aerobic stability of corn silage where pH is low.  Aerobic stability was improved when large amounts of propionic acid (1 to 2% of the DM) were added to silage, but the high percentage of acid often restricted fermentation in these cases.  Propionic acid is difficult to handle because it is corrosive. Hence the acid salts, e.g., calcium, sodium and ammonium propionate have been used.

NUTRIENT ADDITIVES

a)  AMMONIA :  additions resulted in a) addition of an economical source of crude protein  b) prolonged      bunk life during feeding (c) less molding and heating during ensiling; and d) decreased protein  degradation in the silo .

b) UREA : has been added to corn silage as an economical source of crude protein.  A beneficial effect of urea on improved bunk life and decrease in proteolysis has not been totally substantiated.

Ammonia reduces plant proteolysis. Although fermentation is generally stimulated by ammonia, the ensiling processes is prolonged because of ammonia buffering effect resulting in greater total acid production and inconsistent effects on DM recovery. Ammonia can be added at the chopper, blower, bagger or bunk.  In addition, molasses and minerals can be added in these solutions.  Application of anhydrous ammonia should be at approximately 1 kg of N per 100 kg of forage DM  This will increase crude protein from about 8 to 12.5% on a dry matter basis. Anhydrous ammonia should not be added. Water- ammonia mixes or molasses-ammonia mixes should be used. Silage additives can be useful tools to improve silage quality and animal performance, however, they are not replacements for good management practices. Care should be taken when choosing a silage additive.
 
SAFETY IN SILAGE STORAGE
When nitrates are degraded in the ensiling process, nitrogen oxides are formed as products of microbial metabolism. The N02 which results when nitrogen monoxide contacts air is often called "silo gas" and is highly toxic to man and animals when present in concentrations greater than 10 to 25 ppm. Always assume that both C02, and N02, are present in a tower silo and if exposure is not fatal, respiratory tract damage can occur. Relapses are common after apparent recovery.

Since N02 is heavier than air, the brown gas is sometimes clearly visible inside silos or around silo openings. Most of the N02 is evolved from the silage in the first week of fermentation, with production peaking at two to three days after ensiling. Production of N02 essentially stops after the material has been in the silo for more than 10 days. .

FERMENTATION

Fermentation in the silo can be a very uncontrolled process leading to less than optimal preservation of nutrients. Silage additives have been used to improve the ensiling process. Silage fermentation can be divided into 4 phases.

1) The first phase is characterized by the presence of oxygen after forage is chopped and packed in the silo. Plant respiration continues for several hours (and perhaps days if silage is poorly packed) and plant enzymes (e.g., proteases) are active until oxygen is used up.  excess oxygen can lead to unwanted protein breakdown and excessive heating and growth of yeasts and molds that are undesirable. Oxygen must be eliminated by quick packing, even distribution of forage, chopping to a correct length   for optimal fermentation.
2) The second phase of silage under anaerbic conditions is dominated by microbial activity. Fermentation is controlled primarily by: a) type of micro¬organisms that dominate the fermentation, b) available substrate (waster soluble carbohydrates) for microbial growth, and c) moisture content of the crop. During this phase, lactic acid producing bacteria (LAB) should utilize water soluble carbohydrates to produce lactic acid; the primary acid responsible for decreasing the pH in silage. Undesirable fermentations from microorganisms such as Enterobacteria and Clostridia can dominate if the pH does not drop rapidly.
3)  In third phase lack of oxygen prevents the growth of yeast and molds and low pH prevents the growth of most bacteria. Silage can be kept for prolonged periods of time if these conditions prevail.
4) Fourth stage is, feed out and exposure to air. Airtight silos and removal of sufficient silage during feed-out can prevent aerobic spoilage.

Amounts of Common Fermentation End Products in Silages.

 Alfalfa Silage,                   Corn Silage,      Item    

                               30 - 35% DM             35 - 40% DM
 
PH                    4.3-4.5                       3.7 -4.2   
Lactic acid, %                    7 - 8                    4 - 7   
Acetic acid, %                   2-3                      1-3   
Propionic acid, %                   <0.5                      <0.1
Butyric acid, %                    <0.5                      0
Ethanol, %                      0.5 - 1.0                      1-3
Ammonia-N, % of                10-15                  5 - 7    
CP