The Design of the Silage Inoculant: A Key Factor in the Silage Production

These days the price of grain is constantly increasing due to poor harvests in key producing countries, supply constraints on the economy and a fast-growing demand for bio-fuel (UN News Centre, 2006). A price decrease is not expected for the coming years. This is why producers have to extract the highest animal performance from locally produced voluminous feedstuffs such as pastures, silages and industrial by-products.

Preservation of the feed value is an important topic for top animal development. The aim is to inhibit the growth of undesirable microorganisms and the spoilage of the feedstuffs, minimizing the nutrient and energy losses. The main procedures for the preservation of feed are hay making and silage. Silage is the product of the acidification under anaerobic conditions, preferably by means of lactic acid produced by lactic acid bacteria from the plant sugars, of the ensilable material.

The major advantage of silage is that crops can be harvested almost independently from weather conditions. Harvesting losses are fewer and therefore more nutrients are harvested per area. Ensiling permits the use of a wide range of crops (Macaulay, 2003).

The use of silage inoculants has become a common practice over recent years. More and more producers are now using a range of different products which are available on the market. The choice of the right one is a key factor in reaching the expected results.

Use of silage inoculants

Silage inoculants prevent the growth of undesirable microorganisms and therefore the nutrient losses caused by them, and ensure silage feed quality. In consequence, animal performance will be at a top standard level, even in periods of the year in which the availability of feedstuffs is insufficient. Silage inoculants can be classified according to their effect on the matter to be ensiled or their mode of action.

The main effects of inoculants are:

• to prevent undesirable fermentations, and
• to prevent silage spoilage during the feed out phase.

Three different product types are available (as wells as combinations thereof)

• acids,
• their salts or their aqueous solutions, and
• biological silage inoculants.

Other silage additives with more limited use than the three cited above are molasses and enzymes. Salts and acids are used to cause an abrupt decrease in the pH value when the dry matter content of the raw material is out of the optimal range. In cases of low dry matter content, these products inhibit above all, the growth of Clostridia. High dry matter content very often means bad conditions for the compaction of the raw material; air stays inside the ensiled matter, and therefore anaerobic requirements for good silage are not reached. The advantage in the use of salts is that they are non-corrosive and easier and safer in application compared with their corresponding acids.

Design of adequate biological silage additives

Biological silage inoculants have been used and are established on the market because of:

• their proved effectiveness for accelerating fermentation and improving aerobic stability,
• higher recovery in dry matter and energy content compared with non treated silages,
• safety during usage and
• relatively lower cost per treated ton compared with acids.

The quality of good biological silage inoculants must be decided, first, on the basis of the included strains and their proportions in the product. Multi-strain inoculants have the advantages of having the possibility to use different sources of energy and each strain can have a different desirable effect (rapid pH decrease, higher production of lactic acid, or acetic acid production for a better aerobic stability). Therefore it is possible to change the mode of action of a product containing the same strains but with proportions of the bacterial strains. On the other hand, different strains of the same microorganism will grow faster on different substrates, temperature conditions or moisture content (osmo-tolerance).

Another aspect to take into account is the number of bacteria in the product and applied per gram of silage. A review of the products existing on the silage additive market shows a variation from 100 000 to 1 000 000 cfu (colony forming units)/ g silage, with some products even being lower than that.

Most authors agree that bacterial silage inoculants should guarantee at least 100 000 cfu/ g silage (Buckmaster and lundmark, 2008; Kung, 2006). The amount of cfu itself is not a guaranty of bacterial activity (for example, due to their osmotolerance) but in most cases it is an important factor to ensure a quicker and deeper fermentation.

The design of an adequate biological silage additive is a long process in which the strain(s) will be selected permanently, not only under laboratory conditions but also in field conditions. Their effectiveness is based on the activity of living microorganisms, therefore conditions for their growth must be simulated in experiments (dry matter content, quick silo filling, good sealing, etc.). The effectiveness of a biological silage additive can be measured using different methods. Under practice conditions it is very difficult to measure the success in terms of higher performance (milk and/ or meat production) because the whole process is conditioned by many factors.

The first aspect to be taken into account is the silage quality, measured in parameters as pH value, fermentation acids and energy content, compared with the normal values for the ensiled crop or against a negative (no additive) or a positive control, containing a reference additive (see Figure 1).

As shown in Figure 1, the use of Biomin^® BioStabil Plus improved acidification, the production of lactic acid and the energy retention, as well as reduced the butyric acid content, compared not only with the negative treatment (without silage additives) but also with the positive treatments (with silage additives available in the market).

Figure 1: pH values, fermentation acids and energy content of field silages treated or not
(From left to right: negative control, positive control, Biomin^® BioStabil Plus)

The selection of the right biological silage additive will be made taking into account some rules, firstly, the crop to be ensiled. According to the DlG (German Association for Agriculture, 2002) there are three types of crops from the point of view of “ensilability”, which are classified according to their fermentability coefficient (FC):

FC = DM + 8 x sugar content / puffer capacity

• badly ensilable: FC < 35
• ensilable: 35 < FC < 45
• well ensilable: FC > 35

For badly ensilable substrates the recommended biological silage additive should contain (principally) homofermentative bacteria which produce mainly lactic acid, which dramatically reduces the pH value (highly negative correlation coefficient of more than 0.80 between lactic acid content and pH values). For well ensilable substrates as whole maize crop, for example, the aim should be to increase the aerobic stability, because this kind of substrate is very rich in nutrients and spoils very quickly when coming into contact with air and thus with yeasts and moulds (Kung and Ranjit, 2001; Driehuis et al., 1999). This improvement of aerobic stability can be achieved with biological silage additives containing a higher ratio of heterofermentative bacteria for a higher production of acetic or propionic acid and the corresponding inhibition of undesirable spoilage microorganisms (Filya et al., 2004; Dawson et al., 1998). Nevertheless the use of propionate-producing propionic bacteria appears to be less suitable for the improvement of silage aerobic stability, due to the fact that these bacteria are only able to proliferate and produce propionate if the silage pH remains relatively high (Weinberg and Muck, 1996). In Figure 2 temperatures of different maize silages - and as such their aerobic stability - are shown.

Figure 2: Temperature in maize silages with and without silage additives

Composition of the products was: product Biomin^® BioStabil Mays, a blend of homo- and heterofermentative bacteria; product A, a chemical product + L. plantarum; and product B, a chemical product. The control (without any additive) showed an increase of the inner temperature of more than 2 °C after 48 and 53 hours, dame as product B. Treatment with Biomin^® BioStabil Mays proved stable for 168 hours (7 days), which is a sign of the positive effect of heterofermentative bacteria (acetic acid) on aerobic stability.

In recent years, the combination of two or more bacterial strains has become a way to enhance the efficacy and to have a wider spectrum of applicability, for example, new additives which combine homofermentative and heterofermentative bacteria for a better fermentation and aerobic stability (Weinberg et al., 1999).

A product line for better economic results

The product line Biomin^® BioStabil has been designed to take into account the necessity of offering a “solution package” for the producer. The product line Biomin^® BioStabil contains homo- and heterofermentative bacteria for a better fermentation and aerobic stability. Good fermentation is a guarantee of good dry matter and energy recovery. These parameters can be easily translated in animal performance and finally, in money. More importantly than the cost of the product itself is the Return On Investment (ROI), meaning the relationship between the benefits over the cost. An effect on the energy and dry matter recovery was confirmed through the results of many field trials (Figure 1). An economic profit calculation is shown in Figure 3.

Figure 3: Economic profit expected on the basis of a higher energy recovery
(+ 0.28 MJ/ kg DM in 60 tonnes)

Only the extra incomes from milk make a ROI rate of 2.44. If the savings in concentrates for producing the same milk amount are considered, the ROI could reach 5.32.

Conclusions

Silage inoculants cannot replace good ensiling practices. Their use, however, can considerably improve the silage quality, enlarge the aerobic stability and minimize the losses. The inclusion of a silage additive as a routine procedure in farming can substantially elevate the profits of farmers. The most important aspect to take into account is not the price but the Return On Investment (ROI). The most expensive silage inoculants are those which do not have the desired effect on the silage!

References

Buckmaster, D. and B. lundmark (2008): Bacterial Inoculants for silage. Available at: www.age.psu.edu/extension/Factsheets/i/I111.pdf [accessed April 2008]

Dawson, T. E.; S. R. Rust and M. T. Yokoyama (1998): Improved fermentation and aerobic stability of ensiled, high moisture corn with the use of Propionibacterium acidipropionici. Journal of Dairy Science Vol. 81, No. 4: 1015-1021.

DLG (2002): Futterkonservierung. Siliermittel, Dosiergeräte, Silofolien. 6. Auflage, 2002.

Driehuis, F.; W. J. Oude Elferink and S. F. Spoelstra (1999): Anaerobic lactic acid degradation during ensilage of whole crop maize inoculated with lactobacillus buchneri inhibits yeast growth and improves aerobic stability. Journal of Applied Microbiology (87): 583-594.

Filya, I.; E. Sucu and A. Karabulut (2004): The effect of Propionibacterium acidipropionici, with or without Lactobacillus plantarum, on the fermentation and aerobic stability of wheat, sorghum and maize silages. Journal of Applied Microbiology. Volume 97, N 4 (9): 818-826.

Kung, L. Jr. (2006): Consider silage inoculant choices carefully. Copyright 2006 by W.D. Hoard & Sons Company, Fort Atkinosn, WI. Available at: www.qualitysilage.com/PDF/HoardsInoculantArticle.pdf [accessed February 2008].

Kung, Jr., L. and N. K. Ranjit (2001): The effect of lactobacillus buchneri and other additives on the fermentation and aerobic stability of barley silage. Journal of Dairy Science (84): 1149-1155.

Macaulay, A. (2003): Silage Production – Introduction. Available at: www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/for4912 [accessed June 2008].

UN News Centre (2006): World cereal prices surge to 10-year highs due to poor harvests, bio-fuel demand– UN. Avaible at: www.un.org/apps/news/story.asp [accessed June 2008].

Weinberg, Z. G. and R. E. Muck (1996): New trends and opportunities in the development and use of inoculants for silage. FEMS Microbiology Reviews 19 (1): 53-68.

Weinberg, Z. G.; G. Szakacs; G. Ashbell and Y. Hen (1999): The effect of Lactobacillus buchneri and L. plantarum, applied at ensiling, on the ensiling fermentation and aerobic stability of wheat and sorghum silages. Journal of Industrial Microbiology and Biotechnology. Volume 23, Number 3 / September 1999.