This is the first in a three-part series on silage hygiene. Subsequent articles will address management strategies during ensiling and animal health.
An invisible battle between “good” and “bad” microorganisms takes place inside every forage storage structure. If the good guys win, the prize is tons of nutrient-rich silage. If the bad guys win, there may be significant dry-matter and nutrient losses, excessive spoilage, feed refusals, low animal performance or even poor animal health and reproduction. We need the good guys to win!
Livestock producers can tip the balance in favor of more available, more nutritious feedstuffs. Doing so makes all the difference in your operation’s overall profitability. What’s more, many of the recommendations are not expensive or time-consuming and they certainly pay you back.
What are your challenges?
First, it’s helpful to understand what you’re battling. A wide range of microbes naturally occur in standing crop plants (Table 1). They vary in type (bacteria, yeasts and molds), family (Lactobacillaceae lactic acid bacteria), specific species (Lactobacillus buchneri), individual strains (L. buchneri NCIMB 40788) and quantity present. The microbes are influenced by several factors, including:
- Manure and tillage practices
- Crop maturity stage
- Harvest practices
- Field wilting times
Microbes are further influenced by the ensiling process, which includes the ensiling structure, use of an inoculant, speed of filling and covering/sealing.
|Microbial groups||CFU g-1 forage|
|Total aerobic bacteria||> 10,000|
|Lactic acid bacteria||10 to 1,000,000|
|Enterobacteria||1,000 to 1,000,000|
|Yeasts||1,000 to 100,000|
|Molds||1,000 to 10,000|
|Clostridia (endospore former)||100 to 1,000|
|Bacillus (endospore former)||100 to 1,000|
|Acetic acid bacteria||100 to 1,000|
|Propionic acid bacteria||10 to 100|
Plus, plant respiration and the growth and activity of aerobic bacteria while oxygen is present in forages in the ensiling structure cause nutrient losses and prevent a rapid pH drop, in addition to producing heat. These activities are why speed, packing efficiency and sealing are important silage management practices.
Unfavorable anaerobic microbes also may also be present. They can pose a greater problem in competing with natural lactic acid bacteria (LAB) — the “good” silage microorganisms — for dominance during fermentation, especially if there has been prolonged air exposure resulting in the depletion of sugars to drive the lactic fermentation. The negative competitors usually include enterobacteria (including coliforms) clostridia, yeasts and molds.
LAB are important microbes to help ensure a good ensiling fermentation. Specifically important is the presence of homolactic acid bacteria, which rapidly, and only, produce lactic acid from the sugars predominant in ensiled crops. The strongest of the fermentation acids, lactic acid production helps to drop the pH quickly and stabilize forage by creating a low pH environment preventing the growth of mold and yeast.
Unfortunately, LAB are only present in very low numbers in pre-harvest crops. This is why the addition of a research-proven inoculant is recommended. However, inoculants aren’t a magic to positively influence the microbial war during ensiling. Proper management practices will help inoculants prevail in the battle for your ensiled crop.
Manage manure applications
Manure is a valuable recycled nutrient source since it recycles nutrients and helps sustainability. Yet, unsurprisingly, it can also harbor pathogens such as E. coli and clostridia that can negatively affect silage fermentation and feeding performance. Ideally, there should be a 28- to 32-day hay cutting interval from manure application to forage harvest. This common practice reduces the risk of enterobacterial challenges in the resulting silage.
But cutting it too close with the last manure application can set the stage for enterobacteria and/or clostridia, which can compete with LAB in silage fermentation. Additionally, clostridia naturally occur in the soil, which means these fermentations can occur even when the manure application timing was on track. These reasons are why it’s important to be aware of soil inclusion, indicated by ash, in silage analyses. Weather oftentimes doesn’t cooperate, and dry periods immediately after applications can allow enterobacteria to persist into the harvest window because they are attached to the silage crop.
Avoid plant damage in the field
Drought, flooding and pest damage can all stress and damage the plant in the field. Unfortunately, there are no strategies for preventing the effects of Mother Nature. The best recommendation is to understand the potential effects and enact mitigation strategies, especially insect and disease control, where possible.
Crops damaged by any weather event, from flooding to hail or drought, are more prone to mold infestation and subsequent toxin production. Once you see mold growth in silage, a lot of the crop’s digestible nutrients may have already been used by yeasts, which grow first and cause heating. Some of these molds may produce mycotoxins, which can reduce production, affect herd health and fertility, and even be a food safety hazard.
To help minimize silage spoilage, use forage inoculants proven to prevent the growth of specific spoilage organisms and focus on good management practices. Fast filling, effective packing, and covering and sealing the silage help reduce oxygen exposure, protect it from the elements and further decrease the opportunity for spoilage.
Use good harvest practices
The drive to get the most out of your field can often ends up in a trade-off due to potentially lower digestibility and/or bad fermentations resulting in spoilage and waste. Setting harvest height too low can “scalp” the field and contaminate the forage with soil or crop debris. Specific settings also can create a vacuum effect that brings soil into harvested forage, even when the height is correctly set. Merging several windrows can risk bringing in additional soil, as well. Work with your equipment manufacturer’s representative to determine the correct settings for specific crops.
Soil harbors a wide range of undesirable microorganisms, particularly clostridial spores. Therefore, if the forage to be ensiled contains a great amount of soil particles, the risk of microbial contamination and a bad fermentation outcome increase. The level of soil contamination can be estimated in the forage analysis results as ash. As a reference, the respective internal content of ash in corn, grasses and legumes plants is approximately 4%, 7% and 10% on a dry matter basis. Look for a future article discussing the possible animal production and health effects from soil contamination in greater detail.
Watch where you unload
Ash contamination also can sneak in during the filling process. Misjudging pile size or building space can often mean forage is dumped on the ground. Inevitability, this requires scraping the ground to retrieve forage, adding a healthy dose of soil contamination and bad microbes. Poor drainage around the silo, especially by the feeding face, exacerbates this issue (Figure 1).
It is not expensive to keep a log of key metrics like forage analysis ash content, feed intake and silage stability in the feed bunk. These measurements can help determine if additional investments in space, concrete or packing are justified.
Figure 1: Example of poor drainage around the ensiling structure.
Add an inoculant
Simply procuring a fast initial fermentation to get the silage to a low, stable pH can help address many challenges. Aerobic organisms are stifled and can no longer eat up your livestock’s valuable nutrients, and nasty anaerobic bacteria like clostridia and enterobacteria are overwhelmed. In addition, some inoculants contain high-activity enzymes that provide additional sugars for the LAB during active fermentation. These inoculants can also help break down plant fiber, improving fiber digestibility and feed utilization.
During feedout and for more significant challenges including excessive spoilage losses, unstable silage, and suboptimal harvest conditions, it is recommended to include a combination inoculant including L. buchneri NCIMB 40788 applied at 400,000 CFU per gram of silage. This strain has been uniquely reviewed by the Canadian Food Inspection Agency and allowed to claim consistent improvement in aerobic stability. The calculations on inoculant investment, spread over the cost per head per day, are easily justified by the return on investment provided by reputable, research-proven products.
Small changes add up
The forage portion of your ration is one of your most valuable assets. Increasing the amount produced, or buying supplemental feeds, to make up for losses isn’t always a strategy that pencils out. Reducing your dry matter losses by just a few points can make a big difference in your operation’s bottom line.