The goal of silage preservation is to reduce oxygen and increase acidity rapidly, so that lactic acid bacteria grow to stabilize and preserve the forage.
Stimulants, such as bacterial inoculants, sugars, and enzymes, are intended to improve the growth of lactic acid bacteria and their acid production.
Inhibitors, such as propionates, nonprotein nitrogen, and acids, should slow down unwanted silage degradation.
Silage Preservation Goal:
To reduce oxygen and increase acidity rapidly, so that lactic acid bacteria grow to stabilize and preserve or “pickle” the forage.
There are two general categories of silage additives.
A. Stimulants aid in the growth of the lactic acid bacteria and the production of their acids so as to reduce silage pH at a faster rate.
B. Inhibitors help to slow down unwanted silage degradation. For example, inhibitors may reduce mold growth or reduce the breakdown of plant proteins.
A commercial silage additive may contain a number of additive types with different functions. The value of a particular additive will vary depending on the particular situation and needs. It must also be recognized that no silage additive can be expected to make up for poor silage management. Rather, they should be used to enhance good silage management. It has been estimated that about 30-35% of farmers that make silage use preservatives.
1. Bacterial Inoculants are the main type of silage additive used in the U.S (about 70% of all additives). They contain inactive bacteria that become active once they are put on the wet forage. These products are designed to increase the amount of lactic acid bacteria growing in the silage. They contain homofermentative bacteria that produce mostly lactic acid and few of the weaker acids, like acetic and butyric. The objective is to overwhelm the naturally occurring heterofermentative bacteria with the more efficient homofermentative bacteria.
Bacterial inoculants are designed to be able to grow fast under a range of conditions. Their use should increase the rate of pH decline, reduce the final pH of the silage, decrease dry matter losses, reduce protein degradation, and increase overall digestibility of the silage. In regard to aerobic stability (or bunk life), the lower pH of silage with an additive should be beneficial.
In research trials and on farms, it is generally thought that bacterial inoculants have the most significant response when applied to hay crop silage. Increases in acidity and lactic acid are very measurable. Positive changes in dry matter loss, protein degradation, digestibility, and bunk life are more difficult to document. With corn and small-grain silage, the response to bacterial inoculants may be still significant but generally not as large as it is with hay crop silage.
Possible Reasons for Bacterial Inoculant Failure:
a). Sometimes the more beneficial bacteria can be out-numbered by the natural bacteria. Typically, inoculants supply 100,000 CFU (colony forming units) per gram of fresh forage. The population naturally on the forage may be higher than that at times, ranging from 100 to 100 million lactic acid bacteria per gram of fresh forage. USDA research in Wisconsin suggests that the number of inoculated bacteria needs to be 10 times the natural level of bacteria in the fresh forage for the inoculant to be economical. Corn silage tends to have a higher population of lactic acid bacteria than hay crop silage.
b). Sometimes the sugar content of the forage may not be high enough to sustain adequate growth of the inoculated bacteria. This is can be a problem with alfalfa.
c). Sometimes the bacterial inoculant does not grow well if it is added to forage which is different from that which it was isolated from in the laboratory.
d). Inoculant application may have been uneven or application may not have been done according to manufacturer's directions.
e). Sometimes poor management of the silo during feedout can encourage spoilage of preserved silage.
Bacterial Inoculant Application Recommendations:
a). Purchase a product that is labeled for your type of forage or one close to it. Follow package directions.
b). Store in cool location away from sunlight and watch expiration date and package quality. Don’t purchase an inoculant unless its activity is guaranteed. For wilted silage, use a product that provides 100,000 (105)CFU per gram of fresh forage. For wet silage (<20% DM), provide 1,000,000 (106)CFU per gram of fresh forage.
c). Look at the type of bacteria in the product. It should include: Lactobacillus species, Pediococcus species and Streptococcus species. It should not include organisms that break down protein.
d). Use liquid application products rather than dried products for better application. Most inoculants are sold in the dry form but mixed with water for application.
e). If using a bunker silo, apply product at the chopper with a metered sprayer for best application. If using an upright silo, apply product at the blower.
f). Don’t mix bacterial products with chlorinated water (>1 ppm) for application. Chlorine kills lactic acid bacteria.
g). Don’t use prepared inoculant (mixed with water) after 1-2 days.
h). Use bacterial inoculants when you think they will be successful. Don’t use them for everything. Inoculants have the most success on hay crop silage and the least on corn silage. Inoculants will be most successful when silage making conditions are poorer, such as, with shorter wilting times (one day or less), cooler temperatures (60oF (16oC)), and drier forage.
i). Use bacteria inoculants that have been proven by an unbiased test by a university or research institute. There are genetic differences between bacteria. Just like all cows are different, bacteria can be different too.
2. Sugars such as molasses, glucose, and dextrose can be added to forage to increase the lactic acid content of the silage by supplying more food (sugar) for the lactic acid bacteria to grow on. Added sugars can reduce dry matter losses, improve aerobic stability (bunk life) and reduce clostridial spoilage. If used, molasses is added at a rate of 80 lb./ton (4%) to legumes and 40 lb./ton (2%) to grasses. Generally, sugars are not used on corn silage or hay crop silage which is greater than 35% DM.
Enzymes are proteins that speed up the break down of plant carbohydrates to sugars. The sugars that are produced, just like those in molasses, are easier for the lactic acid bacteria to use as a food source to grow on. Hemicellulase breaks down the fiber, hemicellulose. Cellulase breaks down the fiber, cellulose. Pectinase breaks down the fiber, pectin. Amylase breaks down starches. Common sources of enzymes include, Aspergillus oryzae, Aspergillus niger, and Bacillus subtillus. It is critical that the enzymes do their job as fast as possible to provide an immediate food source for the lactic acid bacteria.
If enzymes are added to silage and they do their job, a reduction in ADF and NDF should be seen. Also, an increase in lactic acid and a decrease in silage pH should be seen. There may be a decrease in fiber digestibility because the enzymes will likely digest the easily digestible fiber, leaving the more slowly digestible fiber. Since NEl is usually calculated from the amount of ADF in forage and the digestibility of that ADF is assumed, the laboratory estimated NEl of enzyme treated silage may be higher than actual NEl.
The benefit of enzyme addition to silage is proportional to the amount applied. More is better. Enzymes should be most beneficial in wetter (60-70% moisture) silage. Enzymes take time to work. It is best if treated silage can ferment for at least 3 months to get the most benefit from enzymes. Higher silo temperatures enhance the activity of the enzyme but temperatures over 95oF (35oC) can reduce their effectiveness. Addition of enzymes to corn silage is not recommended because they can have the negative effect of providing too much sugar for yeast growth, producing alcohol and increasing dry matter losses.
Successes with enzymes have been variable. The best results have been seen with cool season grasses. It is recommended that products be used only on forages that they are labeled for and that manufacturers handling and application directions be followed carefully. At this time, enzymes are still a bit of a risky investment. As more research and product development is conducted, it is expected that we will have cost-effective and dependable enzyme products in the future.
1. Propionates (or Propionic Acid) reduce yeast and mold growth. It is often sprayed on silage at feed out time to improve bunk life (aerobic stability). If bunk life is improved, cows will respond with increases in dry matter intake and production.
Some commercial additives for adding at during ensiling, contain either propionates or propionate-producing bacteria (Propionibacterium species). Buffered propionates are available which are easier to handle. Propionate is added at a low rate (0.2-0.4%). Its purpose when added at ensiling is to reduce plant respiration and heating. In the silo, propionates reduce the negative effects of aerobic bacteria, yeasts, and molds, saving dry matter and energy for the cow. If too much propionate is added at ensiling time, lactic acid fermentation may be depressed.
2. Nonprotein Nitrogen (NPN) (Anhydrous Ammonia, Aqueous Ammonia or Urea) is used to improve bunk life (aerobic stability). NPN decreases the growth of yeast and molds. Also, NPN generally shifts the fermentation more in the direction of acetic acid, further enhancing bunk life. This improvement in bunk life from the addition of NPN is fairly consistent among studies. Two other benefits may also occur from the addition of NPN but the results have been variable. NPN may improve fiber digestibility by breaking down some fiber linkages in the silo. Also, the addition of NPN may reduce the breakdown of protein in the silo by making proteases (the enzymes which breakdown protein) inactive.
An added advantage is that NPN increases the crude protein (CP) content in the form of soluble protein (SIP). Typically, NPN isused on high energy, low protein silage such as corn, sorghum, and small grain silage. Cows consuming rations with significant amounts of high-energy silage will generally need the additional of NPN in their diets.
Since high-energy silage generally ensiles easily because of its high sugar content, its fermentation is not greatly compromised by raising the forage pH with NPN (from pH 6 to pH 8.5). Final pH in the stable silage will be either the same as or just slightly higher (0.1-0.2 units) than that of untreated silage but the level of fermentation acids will increase.
NPN addition does increase the risk for clostridia (butyric acid) fermentation, especially in low sugar silage such as alfalfa. More sugars are needed to increase acidity and stabilize silage which has been treated with NPN. Without that sugar, pH will be high and clostridia will thrive.
Ammonia is better than urea for improving bunk life. Anhydrous ammonia is generally added at the chopper at a rate of 7 pounds/ton of wet forage (0.35%). It should be handled with care as it can cause lung damage and burn the eyes.
Urea is more slowly available in the silage. Enzymes in the forage convert the urea to ammonia and carbon dioxide. Urea is used at a rate of 10-20 pounds/ton of wet forage (0.5-1%). It is generally used if the desire is more to increase crude protein than to improve bunk life.
3 Acids (Formic Acid / Formaldehyde, Sulfuric Acid) are used to immediately drop silage pH and stop the activity of enzymes and bacteria. Generally, these products are applied to high-moisture silage (>70% moisture) which would otherwise be at risk for a clostridial fermentation and protein degradation. Often, sugars (most often molasses) are added in conjunction with acids.
Kung, Jr., L. 1991. Silage additives: Microbial inoculants and enzymes. Proceedings of the 1991 Western Canadian Dairy Seminar, Red Deer, Alberta, Canada.
Mahanna, B. 1997. Silage Fermentation and Additive Use in North America. Pioneer Hi-Bred International, Inc. Website (www.pioneer.com)
Muck, R.E. and Kung, Jr., L. 1997. Effects of silage additives on ensiling. Proceedings of the Silage:Field to Feedbunk North American Conference, Hershey, PA.
Pitt, R.E. 1990. Silage and hay preservation. Northeast Regional Agricultural Engineering Service. Ithaca, New York.
Shaver, R. Silage preservation - The Role of Additives. University of Wisconsin, Cooperative Extension. A3544
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