Silage is a forage crop preserved by "pickling" in acid. By packing the crop tightly into a silo and excluding oxygen, plant sugars can be fermented into acid by anaerobic bacteria. Although most crops carry a sufficient population of natural bacteria to produce silage, there is no control over the type of acid produced or how long the process takes.

Time is a key factor as rapid fermentation stops crop nutrients from being consumed by undesirable microorganisms present. The longer the process, the greater the in-silo losses of dry matter and energy, which leaves less nutrients available to cows. The type of acid produced has a major impact on the speed of preservation and the palatability of the resultant silage. The aim of forage inoculation is to allow livestock producers to take control of the fermentation by bombarding the crop with friendly "bugs" that produce the appropriate acid in the fastest possible time.

Effective inoculants can provide a highly cost-effective means of maximizing the quality of silage retained in the bunker or silo.

Efficacious inoculants preserve a high level of crop nutrients, produce a palatable silage with a high intake potential, and, most importantly, increase the amount of milk (or weight gain) produced from each ton of forage.

Do Silage Inoculants Work?

Despite these economic advantages, less than half of the silage produced annually in the U.S. is treated with an inoculant. This suggests many producers have not been convinced inoculants improve profitability. Producers are faced with two obstacles:

     It is often difficult to visually observe differences between treated and
     non-treated silages.

     Reliable on-farm evaluations are extremely difficult to conduct, 
     if not impossible due to the wide range of variables involved.

An untreated, excellent silage might be even better if treated. Likewise, poor-quality silage might be worthless if untreated. To determine whether inoculation is effective, producers can rely on independent researchers who have the skills and resources needed to conduct replicated trials. However, taken as a whole (all research, across all forages and inoculant types), the scientific record does not present a very convincing case in favor of inoculation.

A recent literature review, conducted by U.S. researchers, found the majority of published trials showed little positive benefit from silage inoculation. The review, "Animal Response to Silage Additives" by Dr. Limin Kung and Dr. Richard Muck, found only 28% of inoculant studies showed an increase in silage intake and only 47% showed an increase in milk production. Given this scientific evaluation of a one in four chance of intake improvement and a 50:50 chance of improved animal performance, it is not surprising many producers remain unconvinced that silage inoculants can offer any real economic benefit.

However, closer scrutiny of the data reveals the scientific message is that some inoculants do offer real practical advantages. Among the many inoculants available, the review identifies three which appear to deliver reliable performance and identifies one organism, MTD/1, as being particularly well-proven.

Variation in Performance

So, what might account for this variation in performance among inoculants? What factors are responsible for inoculant effectiveness? Three factors appear to be crucial:

     The natural abilities of the bacteria involved.

     The number of bacteria applied.

     The stability of the inoculant when used on the farm.

Nearly all inoculants contain one or more species of lactic acid producing bacteria. Lactobacillus and Pediococcus species, such as L. acidophilus, P. acidilactici, and P. pentocaceus, are frequently found in mufti-bug products and Enterococcus faecium (also called Streptococcus faecium) may also be included. These bacteria are all able to grow rapidly at a range of temperature and moisture levels and all produce lactic acid, the best type of acid for preserving forage.

Lactic acid is relatively strong and its production in the bunker or silo causes pH to drop quickly, which is essential in the rush to kill-off less desirable organisms before they can consume valuable nutrients and dry matter. It also has the advantage of being a highly palatable nutrient. However, there are differences among strains of L. plantarum.

Occasionally, acetic and propionic acid-producing bacteria are used because these acids have anti-fungal activities, but their use often results in substantial in-silo losses and a higher final pH. Although highly acetic silage may show some resistance to aerobic spoilage, both acetic and butyric acid are associated with poorly preserved, bad smelling silage with low palatability and intake.

The need to use lactic acid producing bacteria has been established, but which ones and how many? For maximum speed, bacteria should start growing immediately, grow fast, and produce an abundance of acid. L. plantarum is a highly efficient lactic acid producer found in most inoculants and grows vigorously at pH 5.3 and below. Unfortunately, since most crops have a pH of around 6.5 when cut, L. plantarum is generally a slow starter.

Single Bug Versus Multi-Bug

The use of "helper" bugs (typically Pediococcus and/or Enterococcus species) which grow at the initial crop pH are sometimes included with L. plantarum inoculants. Although the helper bugs might not be the fastest or most efficient producers of lactic acid, they are able to grow during the early stages of fermentation, reducing pH down to a level at which L. plantarum becomes more effective. Such multi-bug products are certainly an improvement over late starting, single-bug inoculants as they can impact the fermentation process from the onset. But this compromise solution has several flaws; the most important of which is the organisms' ability to dominate the microenvironment within the stored forage.

All crops contain high populations of microorganisms that, in addition to wasting nutrients, produce undesirable end products including acetic and butyric acid, ethanol and amines, which significantly affect feed value. This is why most inoculants apply 100,000 colony forming units or CFU (organisms) per gram of fresh crop, a threshold at which domination of the silage fermentation is most likely. Any product supplying less than 100,000 CFU should not be considered as the chances of it gaining control of the fermentation process from high populations of "resident" bacteria is limited.

The problem with "better" multibug products is that, although they may provide the requisite numbers of bacteria, they are not all working at the same time. For instance, a typical inoculant "cocktail" of 50% Pediococcus and 50% L. plantarum may have a total application rate of 100,000 CFU per gram of forage, but during the crucial early stages of fermentation (pH 6.5 to pH 5.3), it is only the 50,000 Pediococcus that are doing anything worthwhile.

The Strain

Clearly, the ideal solution is to use bacteria that are highly efficient producers of lactic acid and and have the robustness and flexibility to maintain rapid growth from the moment they are applied to the crop, right through to the completion of fermentation. This is asking quite a lot of a single cell organism given the range of conditions that exist within a pile of fermenting forage. The temperature can vary considerably, as can the moisture content (depending on the age and type of crop ensiled) and the weather conditions at the time of harvest. But, the most challenging aspect remains the huge change in pH, starting with a fresh crop at pH 6.5 and finishing with a well preserved silage that may have a pH as low as 3.8.

Just as there are major differences between different breeds of cattle (Herefords and Holsteins are both members of the same species, but they are obviously not the same), there can be major differences among individual strains of a single bacterial species. Many strains of Lactobacillus plantarum are commercially available. They have basic similarities, but also important differences that make each strain unique. Strains vary in their ability to produce lactic acid, grow over a wide temperature and pH range, and survive manufacturing processes, storage, transport, and application. This explains why some inoculants work better than others.

MTD/1

MTD/1 is a high performance strain of L. plantarum that has a number of unusual features, making it ideal for a silage inoculant. As well as being a highly efficient producer of lactic acid over a pH range from above pH 7 to below pH 4, it grows within a wider temperature and pH range than many other strains. It is also very osmo-tolerant, so that it works equally well in high- and low-moisture conditions.

The ability to grow in aerobic as well as anaerobic conditions gives it a head start on strictly anaerobic bacteria which cannot grow until air is excluded from the forage. MTD/1 is active when it is applied to the crop. These natural advantages make MTD/1 an ideal single strain inoculant that starts to work immediately and stays in control throughout the fermentation process. Its ability to thrive within a wide range of crop moisture and sugar situations means it is equally effective on a variety of crop types and harvesting conditions.

In the 1999 U.S. Direct-Fed Microbial, Enzyme & Forage Additive Compendium, Dr. Kung summarizes 14 lactation studies conducted in university and government research institutes in North America and Europe using MTD/l. His paper, "Use of Additives in Silage Fermentation," identifies significant improvements obtained with a variety of crops (grass, corn, alfalfa) across a wide spectrum of dry matter contents (15-46% DM).

Cultured Growth

The bacterial content alone does not totally account for an inoculant's efficacy. Just as important is the process of preserving the organisms so they are still alive when applied to forage. Once a strain has been selected, the bacteria have to be grown in large numbers, preserved, and stabilized-processes that determine bacterial survival and product performance.

Most products are produced by batch culture, in which bacteria are added to a measured quantity of nutrient mix and grown in large vessels called fermenters. When the nutrient mix is depleted, bacteria stop growing, are emptied from the fermenter, and the next batch is set to run. When bacteria are harvested at the end of the process, they may be at varying stages of their growth cycle, and in various states of health. This can affect their ability to survive and their speed of revival and activity when applied to forage. Also significant variation can occur from batch to batch.

An alternative method, continuous culture, is more complex, demanding a high degree of technology and expertise, but overcomes the problems of variability. It uses a special fermenter that allows a continuous feed of nutrients and continuous harvesting of bacteria at a specific stage of the growth cycle. This ensures both consistency and unparalleled vigor as it enables each bacterium to be harvested at peak fitness. This process helps organisms survive the rigorous conditions of freeze-drying while ensuring their ability to immediately start producing lactic acid once applied to forage.

Death or Stability

Freeze-drying, the usual method of bacterial preservation, is an aggressive technique that requires great expertise to ensure bacteria survive and are capable of rapid and full reactivation. Several studies have revealed significant shelf life problems with some inoculants (low bug counts by the time the product reaches the producer and poor storage properties on farm). Some manufacturers accept a high mortality rate and try to compensate by overformulating or by declaring a short shelf life. Others have developed methods to protect bacteria during preservation, so that their product remains alive during storage and transit.

One company, ECOSYL Products, has patented a process that encloses each bacterium in a protective shell to give added protection during freeze-drying and to aid rapid recovery on re-hydration. The shell contains special ingredients which, on contact with moisture, releases nutrients to jumpstart the bacterium so that it re-activates quickly.

Stability is a good indicator of an inoculant's ability to survive and produce good results on farm.

The level of stability can be identified by the declared shelf life. Products containing MTD/1 have a shelf life of three years; whereas, a claimed shelf life of between three and six months is typical of most inoculants.

Making a Choice

Silage inoculation should be a routine procedure in all forage production systems. An inoculant's efficacy depends on:

     The natural ability of the organisms to produce high levels of lactic acid 
         across the full pH range of crop preservation.

    An application rate of 100,000 CFU per gram of forage, all working 
       at the same time.

    The manufacturers' ability to provide a consistent, stable product so 
        the organisms are still alive when applied to forage.

The easiest way to choose a product is to simply ask for proof of the inoculant's performance. Additive claims based on the results of just a handful of trials lack depth and do not demonstrate the consistency with which the benefits may be achieved on-farm. MTD/1 provides a good benchmark as it is supported by over 150 independent trials showing improved fermentation, over 20 trials showing reduced fermentation losses, and is the only bacterial inoculant in the U.S. to have fermentation claims recognized by the FDA's Center for Veterinary Medicine.

MTD/1 in the USA

The high performance bacterial strain MTD/1 is only available in ECOSYL®* Silage Inoculant. Distributed by Alliance Nutrition.  ECOSYL is provided as both a dry-applied granular product and as a powder for liquid application following dilution in water. Proven for the effective treatment of corn, alfalfa, grass, high-moisture corn, sorghum, and all small-grain cereal forages, a standard bottle of ECOSYL Silage Inoculant treats 54 tons of forage.

A new super concentrated product, ECOSYL Concentrate, is now available for larger operations. Delivered in the same size bottle and regular ECOSYL,one bottle of ECOSYL Concentrate has four times the treatment capacity of the standard bottle. By treating 200 tons per bottle versus 50 tons per bottle, producers can save time and labor in mixing and cut on-farm storage, handling, and disposal of bottles by 75%.

The mixing rate for ECOSYL Concentrate is one bottle per 140 gallons of water and applied at a rate of 1/2 gallon per ton of silage. ECOSYL-DG provides MTD-1 in dry, granular form (50 lb bags). One 50-Ib bag of DG will treat 50 tons of forage.

* ECOSYL is a registered trademark of ECOSYL Products Ltd.