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Article written by Lucas Mari, mVeterinarian, PhD in Animal Science and Pastures, gTechnical Support Manager for South America – Lallemand Animal Nutrition
The word "heterolactic" may not be part of everyone's common vocabulary, but it refers to a group of bacteria used in silage inoculants, whose main purpose is to control the heating of the silage after it has been opened for consumption. The first species of this bacteria used was... Lactobacillus buchneri (now Lentilactobacillus buchneriThis has been happening since the late 1990s, especially in corn silage, whether as whole plant or grain silage, but also in various other cereals and in sugarcane silage with great success in Brazil since the early 2000s. More recently, another major innovation in the market has been the use of... L. buchneri associated with L. hilgardiiwith results that are far more significant than L. buchneri isolated.
The main objective of using these heterolactic bacteria is to control aerobic stability through the production of acetic acid during fermentation. In a more detailed analysis, the production of this acid is responsible for inhibiting the growth of yeasts, the first microorganisms that cause spoilage when open silage is exposed to atmospheric oxygen.
It is still necessary to clarify that there is a minimum limit that the scientific literature recommends as inoculation for the purpose of controlling silage temperature after opening; this level is 100,000 colony-forming units (CFU)/g of silage. This was evaluated in a meta-analysis by researchers and the EFSA (European Food Safety Authority) in 2013.
In addition to the effect of L. buchneri Whether or not associated with L. hilgardii in yeast control and, consequently, in aerobic stability, heterolactic bacteria have recently demonstrated positive effects in improving starch digestibility and in controlling fungi and, consequently, mycotoxins.
Effect on starch digestibility
Corn silage, whether whole plant or grain, is characterized by improved starch digestibility over time; that is, the longer the silo remains closed, the greater the degradation of a prolamine protein called zein. Zein acts as a cement between the starch granules, hindering their degradation.
In a study with rehydrated corn silage, researchers concluded that more than 60% of zein degradation is due to silage bacteria, almost 30% by enzymes in the corn kernels themselves, and the remaining 10% are divided between fungi and fermentation acids (Figure 1).
Figure 1 – Contribution to proteolysis in rehydrated corn silage
In 2018, new research verified that silages inoculated with heterolactic bacteria (L. buchneri) had even more effective DM degradability. Non-inoculated rehydrated corn grain silages showed DM degradation of approximately 79%, while inoculation with homolactic bacteria showed 82% and of L. buchneri Inoculated at 100,000 CFU/g of silage, the DM degradability increased to 83.6% (Figure 2). Comparing this last bacterium with the control silage, this would be almost 5 percentage points, or almost 6% of improvement. In this way, we are practically talking about an equivalent of one sack of corn for each ton of silage inoculated with L. buchneri.
Figure 2 – Dry matter degradability after 12 hours of ruminal incubation of corn silages inoculated or not with homo- or heterofermentative bacteria.
In comparison to the results shown, a study conducted at the Federal University of Lavras evaluated the inoculation of corn ear silage (snaplage) with L. buchneri + L. hilgardiiThe benefit compared to non-inoculated silage was even greater, reaching 9 percentage points (91.5 vs. 82.5% of starch degradability in 7h of ruminal incubation).
It is therefore demonstrated that it is possible to improve aerobic stability with the use of L. buchneri and L. buchneri associated with L. hilgardii and have the added benefit of greater starch degradability. Given the current global corn prices, it's easy to calculate and see that the return on investment for this type of inoculant is very positive, even considering only this aspect.
Effect on fungal control and mycotoxin production
The effect of controlling fungi and yeasts by Lactobacillus buchneri This is also well documented. An assessment conducted by scientists at INTA Salta in Argentina was published in the International Symposium on Forage Quality and Conservation in 2019. The treatment with L. buchneri It reduced the count of fungi and yeasts and improved aerobic stability, as can be seen in Figure 3.
Figure 3 – Fungal and yeast count and aerobic stability in whole-plant corn silages evaluated in Argentina.
One expected consequence of fungal control in silage may be a decrease in mycotoxin production. Researchers at IRTA Barcelona, in Spain, inoculated corn plants with Lactobacillus buchneri and compared it to fresh forage before silage and control corn silage. It can be observed that inoculation with the heterolactic bacteria L. buchneri was responsible for controlling the production of the two mycotoxins evaluated: aflatoxin (Figure 4) and zearalenone (Figure 5).
Figure 4 – Aflatoxin levels in fresh forage and silage, either uninoculated or inoculated with L. buchneri
Aflatoxin is considered a storage mycotoxin, so it was expected to develop while the forages were fermenting, if we're talking about that process. The opposite happened; there was a decrease in mycotoxin levels in both cases, even in the silage inoculated with... L. buchneri These levels were even lower, most likely due to greater inhibition of fungal growth.
Figure 5 – Levels of zearalenone in fresh forage and silage, uninoculated or inoculated with L. buchneri
In turn, zearalenone, which is a mycotoxin linked to reproductive damage in animals, mainly females, is produced by Fusarium spp., a fungus considered to grow in the field, but what was observed in this study was that there was an increase in levels during storage; fresh forage showed less ZEA than silage. Even so, the silage without inoculant showed a higher ZEA 10% level than that observed in the inoculated silage. Lentilactobacillus buchneri.
Final considerations
As we have seen, far beyond just the desirable effect in terms of aerobic stability, silages inoculated exclusively with heterolactic bacteria showed improved starch digestibility and control of fungi and their mycotoxins. Therefore, to calculate the return on investment, it must be evaluated according to the multiple positive responses.
Bibliographic references are with the author. Contact: jmoro@lallemand.com
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