- Dairy and beef cattle
- Ruminants
How can forage be preserved with silage preservatives?
Forage preservation is a strategic stage in livestock farming. Its success will subsequently determine the quality of cattle feed ans therefore animal health and performance. What do we expect from good forage? It should be palatable, healthy, digestible and energy-rich. To achieve this, particular attention must be paid to its preservation.
So, what happens during the silage preservation process once forage has been harvested? Why is it recommended to add a preservative? What is its role? Which one should you choose?
In this article, you will find all the answers to these questions to help you make an informed choice.
With forage making up 70 to 80% of a ruminant's ration, its nutritional value is clearly of real importance. Grass, cereals, cereal mixtures, protein crops and legumes are all types of forage grown on farms, and their proper preservation must be ensured.
Many factors influence the preservation of grass or maize sillage, and it is not always easy to control contamination in the field. Weather conditions, the impact of previous crops, soil cultivation and the varieties chosen are all variable factors. Harvest stage, cutting height and compaction of the clamp are preparation stages that determine forage preservation.
It is therefore essential not to leave to chance what happens under the sheet once the air has been removed and the silo has been sealed. Silage preservatives helps secure the preservation process. The most common storage method on farms today remains bunker silo storage. This method preserves forage through anaerobic fermentation, meaning without air.
Bale wrapping is an additional technique, but the same fermentation processes occur, except that each bale acts as a mini silo in itself and the fragility of the film creates points of deterioration, such as damage from loader grabs during handling, bird pecks or rodent teeth.
What happens under the sheet?
The major role of bacteria
To ensure good preservation, the aim is to limit the development of moulds and putrefactive bacteria, while promoting the development of lactic acid bacteria.
When a bunker silo is closed and properly sealed, the fermentation process begins and goes through several phases:
- The aerobic phase: 1 to 5 days
- The transition phase: 5 to 15 days
- The acid fermentation phase: 15 to 21 days
- The stabilisation phase: more than 4 to 6 weeks
For good preservation, lactic fermentation is the desired process, because the main objective is to lower the pH of the silage. A pH that remains high after 2 to 3 weeks is a sign of insufficient or deficient fermentation. The lower the pH, the more it encourages the development of acidophilic bacteria.
Despite compaction, there is always some oxygen left in the silo. This is why there is an initial aerobic phase, during which enterobacteria present on the plant and fungi consume this oxygen. Once the air has been consumed, they die off and make way for lactic acid bacteria, which are anaerobic, meaning they develop in the absence of oxygen. This marks the beginning of the acid fermentation phase.
These bacteria are already naturally present on forage leaves and stems. They digest sugars and certain simple proteins and convert them into lactic and acetic acid. The mode they develop and the greater their numbers, the more the pH falls and the better the preservation. This is why adding more of them speeds up the maturation process.
- Lactic acid allows a rapid drop in pH, and it is precisely this phenomenon that ensures good forage preservation. It also improves palatability, as it gives forage a pleasent nutty smell.
- Acetic acid inhibits the development of yeasts, and moulds to a lesser extent, particularly when the clamp is opened. Controlling yeast development is essentials. As they grow, yeasts produce ethyl alcohol, which the female's liver will then have to detoxify. In short: too much alcohol means greater palatability at first, followed by less milk later on.
Why add a preservative to silage?
For one simple but essential reason: to avoid losses in the silo. Without a preservative, dry matter loss is estimated at 12 to 15% on average. With an acid preservative, it is around 4 to 5%, and with a bacterial inoculant, the loss falls to 6 to 8%. When considered across the total area of a field, this is far from insignificant.
The second reason is that using a preservative limits heating when the silo is opened and helps keep forage stable at the feed bunk. When the silo is closed, everything is balanced and stable, with no oxygen left. When the silo is opened, oxygen is introduced massively and fermentation restarts.The lactic and acetic acids produced during the ensiling process are not sufficient to prevent fermentation from restarting, unless a heterofermentative bacterial preservative is used to allow greater acetic acid production in the silo.
Using a preservative means:
- Either adding the lactic acid bacteria the forage needs to be properly preserved. The more numerous they are, the more effective they are, but only if they have enough available moisture to develop.
- Or adding a blend of organic acids that enables a very rapid, almost immediate, drop in pH.
- It also means being able to use the silo much sooner than without adding a preservative, saving 2 to 3 weeks.
What are the health risks linked to poor fermentation?
When fermentation does not take place properly in the silo, this is known as fermentation deviation. Pathogenic microorganisms may then develop, and their presence can have serious consequences.
Moulds
Moulds are present when ensiled forage is dry and poorly compacted.
They can lead to refusals at the feed bunk and increase the risk of mycotoxins, which can disrupt rumen flora and cause infertility or abortion.
Yeasts
Yeasts are present when forage compaction has not been sufficient. They consume digestible sugars and produce ethyl alcohol, which initially increases palatability before causing a sharp drop in forage palatability and refusals due to intoxicated livers.
Butyric bacteria
Butyric bacteria are present when soil is incorporated into the forage during harvesting, or when acidification is too slow. They are recognisable by their strong smell.
These microorganisms can have a significant economic impact, as affected parts must not be consumed by cattle and have to be discarded. To avoid this loss, it is recommended to add a silage preservative.
How to choose your silage preservative?
There are two types of preservatives: bacterial inoculants and acidifiers. In both cases, they are sprayed at harvest using pumps or applicators integrated into forage harvesters.
Bacterial preservatives
They are also known as inoculants or biological preservatives.
They enrich silage with lactic acid bacteria to stimulate and accelerate preservation.
There are two types of lactic acid bacteria: homofermentative and heterofermentative. In all cases, they need a certain level of moisture in the substrate in order to develop.
Homofermentative bacteria:
These bacteria produce a single type of molecule: lactic acid. They allow the pH to fall very quickly and provide a rapid preservation effect, which is of course very important, but not sufficient. They are not antifungal and must therefore be supplemented.
The most common are: L. plantarum, Pediococcus pentosaceus.
Heterofermentative bacteria:
These bacteria produce two types of molecules: lactic acid and acetic acid. They are mainly involved in the second phase of preservation. Their key characteristic is that they inhibit yeasts and moulds thanks to their antifungal effect.
Examples include L. buchneri, L. brevis, L. diolivorans...
These two types of bacteria, homofermentative and heterofermentative, complement each other and act differently but effectively over time. A preservative will be fully effective if it contains both families of bacteria. If it contains only one bacterial strain, its action will be incomplete and therefore less relevant.
Our biological preservatives: SILOGUARD H/SP and SILOGUARD M/SP.
Focus on the bacterium L. diolivorans
“It is a fairly recent strain with the advantage of acting very quickly and aggressively. It is the strain that allows the silo to be opened from the 14th day of fermentation without any risk of heating. It prevents losses at opening. Its presence in a preservative is a real asset.”
Acidifying preservatives
Organic acids are used more when silage is produced under difficult conditions:
- When dry matter is low, below 25%, or on the contrary too high, above 40 to 45%, due to poor compaction, insufficient chopping or persistent oxygen.
- When forage has a high buffering capacity that works against acidification through fermentation, for example when crude protein is too high. This may occur with a high proportion of clover, birdsfoot trefoil or lucerne in addition to grasses, or in mixed cereal-protein crops.
- When forage is low in sugars, which would prevent good lactic fermentation.
Under these conditions, the silo is exposed to greater risks: putrefaction linked to the development of enterobacteria and the risk of mould development. It is then necessary to use a more appropriate and versatile product. Whether the substrate is dry or moist, whether the weather is hot or cold, the results are there. The application is slightly more demanding, requiring protective equipment during application and the handling of larger volumes.
It is important to assess the risks, because depending on the composition of the acidifier, the action will be more focused on fungi, bacteria or balanced between the two. As a reminder, formic acid lowers pH and has a mainly antibacterial action, whereas propionic acid prevents the development of moulds and yeasts. In addition, depending on the form in which they are supplied, the product will be more or less corrosive and more or less volatile.
They are also particularly effective on silo faces. They are also suitable for mixed rations, where exposure to air during preparation and distribution reactivates the development of microorganisms, especially in high temperatures.
The choice of preservative therefore depends on several factors: geographical area, weather conditions, quality of the silage-making process and type of forage.
Did you know?
- Forages are more or less easy to preserve depending on their sugar content and buffering capacity, because buffering capacity works against acidification. The richer the forage is in sugars, the easier it is to acidify; the richer it is in protein, the more difficult it is to acidify.
- Chlorinated mains water can kill the bacteria in certain preservatives. This is therefore an important point to check when purchasing the product and when preparing the inoculant/water mixture.
