Preventing Silage Spoilage: Tips to Ensure Quality and Longevity

Silage is one of the most effective ways to preserve surplus forage for livestock, but the entire effort falls apart if spoilage takes hold. Once silage deteriorates, there is no way to restore its quality – spoiled silage must simply be discarded. The good news is that spoilage is largely preventable. With the right understanding of what causes it and the right management practices in place, you can protect your silage from the moment of ensiling right through to the point of feeding.

Understanding the causes of silage spoilage 🔗

Silage preservation works on a straightforward principle: lactic acid bacteria (LAB) ferment the sugars in the forage under anaerobic (oxygen-free) conditions, producing lactic acid that drops the pH and creates a stable, low-oxygen environment hostile to spoilage organisms. When this process is disrupted, spoilage follows.

Oxygen ingress 🔗

Oxygen is the single biggest enemy of quality silage. Oxygen infiltration through cracks, punctures, or poor sealing allows aerobic microorganisms – primarily yeasts and molds – to grow freely. As University of Wisconsin extension educators explain, yeasts consume nutrients and lactic acid as energy sources, which triggers a chain reaction: the silage heats up, volatile acids are lost, pH rises, and molds proliferate, ultimately destabilizing the entire mass. Even densely packed silage can undergo aerobic spoilage once air gains access.

Delayed pH drop and microbial contamination 🔗

If the silo is filled too slowly or the forage has insufficient fermentable sugars, the pH does not drop quickly enough during the early stages. This delay gives undesirable bacteria – including Enterobacteriaceae, Clostridia, and butyric acid-producing organisms – time to establish themselves. According to research reviewed in Benison Media, temperature fluctuations, oxygen availability, and the pace of pH decline during early fermentation all govern whether butyric acid forms in harmful quantities. Butyric acid-contaminated silage reduces palatability and dry matter intake in cattle, and can contribute to metabolic conditions like ketonemia.

Soil contamination and poor-quality material 🔗

Soil entry into the silage pile is a direct route for pathogen and butyric acid bacteria contamination. Crops should be harvested at least four weeks after manure application, and harvesting should be done carefully to avoid soil pickup. Using immature or poor-quality plant material at ensiling also weakens fermentation from the start, because immature crops may lack sufficient fermentable carbohydrates to sustain adequate LAB activity.

Proactive measures to control air exposure 🔗

Because oxygen is the primary driver of spoilage, preventing its entry into the silage mass is the foundation of any spoilage control strategy.

Proper packing and sealing 🔗

Effective compaction minimizes gas-filled porosity in the silage mass, maintaining anaerobic conditions and reducing the foothold available to aerobic spoilage organisms. Once packed, the silage must be sealed immediately. Horizontal silos should be covered with plastic immediately after filling and weighted to prevent air infiltration under the cover. Plastic covers must be weighted across the entire surface – typically with tires placed so they touch on all sides – and the edges must be secured to prevent billowing. Billowing plastic acts like a bellows, actively pumping air across the silage surface and greatly accelerating spoilage.

For bunker and trench silos, oxygen can permeate concrete walls and floors, especially through cracks. Lining the floor and walls to create a tight seal, and keeping all cracks repaired, is essential. Acids produced during fermentation can damage concrete over time, so regular structural inspection is necessary.

Silo bag management 🔗

Silo bags offer flexibility, but they are vulnerable to punctures from equipment, animals, hail, and wildlife. Each bag should be inspected weekly and any holes repaired with distributor-supplied tape. Bags should be located away from trees and fenced lines, weeds should be mowed around the storage pad, and spilled feed should be cleaned up promptly to discourage rodents. Placing bags on a firm base – such as concrete or packed limestone screenings – also limits soil contamination and reduces moisture wicking from below.

Regular inspections during storage 🔗

A consistent inspection schedule is not optional – it is a core management task. Plastic covers on bunkers and piles should be inspected weekly, with any punctures or tears repaired using oxygen-excluding tape. Water entering the silage through cover failures carries oxygen to aerobic organisms and washes out soluble sugars and acids, raising pH and accelerating deterioration. Covers should be installed and maintained so that rainfall is directed away from the silage mass.

Using additives to limit silage spoilage 🔗

Silage additives are a well-researched tool for compensating for fermentation deficiencies and suppressing spoilage microorganisms. They fall into two broad categories: biological inoculants and chemical additives.

Biological inoculants 🔗

Microbial inoculants contain selected strains of lactic acid bacteria applied to the forage at ensiling. Homofermentative inoculants such as Lactobacillus plantarum and Pediococcus species drive a rapid pH drop, inhibiting undesirable bacteria and preserving plant proteins. They shift fermentation toward lactic acid, reduce ammonia nitrogen production, and can improve dry matter recovery by 2-3% compared to untreated silage.

However, homofermentative inoculants do not always improve aerobic stability during feed-out – in fact, in corn silage, their use can sometimes increase heating problems at the face because the lactic acid they produce can be consumed by lactate-assimilating yeasts when oxygen is reintroduced. Heterofermentative bacteria, particularly Lactobacillus buchneri, address this problem by producing acetic acid – a stronger inhibitor of yeasts and molds – which significantly improves aerobic stability during feed-out. The trade-off is slightly higher fermentation losses and a slower pH decline. L. buchneri requires 45-60 days of storage before its effect on aerobic stability becomes meaningful, so it is not a solution for immature or freshly opened silage.

Bacterial inoculants also produce antimicrobial substances including hydrogen peroxide, ethanol, diacetyl, and bacteriocins that limit pathogen development in the silo, adding a further layer of protection beyond pH reduction alone.

Chemical additives: acids and salts 🔗

The active ingredients in chemical additives are acids and their salts, principally formic acid, propionic acid, sorbic acid, benzoic acid, and acetic acid. Formic acid acts through direct acidification of the silage mass, suppressing clostridia and other undesirable bacteria from the outset and improving protein preservation during ensiling. Propionic acid and its salts (calcium, sodium, and ammonium propionate) target yeasts and molds – the primary aerobic spoilage organisms – and are particularly effective at improving aerobic stability during feed-out.

Benzoate and sorbate inhibit yeasts and molds and are often used alongside homofermentative inoculants to address the aerobic stability gap those inoculants leave. Silage additives containing partially neutralized acids in salt form – such as nitrites and sulfates – combined with formaldehyde-based preservatives are also used commercially, though health and safety considerations have driven a gradual shift toward biological and organic acid alternatives. Sodium nitrite is specifically useful for inhibiting enterobacteria and clostridia while promoting natural lactic acid fermentation.

The choice between additive types should be guided by the specific problem being addressed. If the primary concern is poor fermentation due to low sugar content or wet forage, a fermentation stimulant such as molasses or an enzyme-based additive may be more appropriate. If aerobic spoilage during feed-out is the issue, propionic acid or an L. buchneri inoculant is the better fit.

Best practices for handling and storing silage 🔗

Even well-made silage can deteriorate rapidly if it is handled or fed out incorrectly. Managing the feed-out phase is just as important as managing the ensiling phase.

Feed-out rate and face management 🔗

Once a silo is opened, the exposed face becomes vulnerable to aerobic spoilage. Recommended minimum removal rates are 4 inches per day from tower silos, 6 inches per day from bunkers and piles, and 12 inches per day from silage bags. At these rates, the silage being fed has had minimal contact time with air, and the average dry matter loss across the removed feed is significantly lower than at slower removal rates. Silage with a packing density below 13 lb/ft³ will require an even faster feed-out rate to keep spoilage in check.

Plastic covers on bunkers and piles should not be rolled back more than three days of feeding at a time, and the leading edge of plastic should be kept secured to the silage surface with tire sidewalls or sandbags to prevent billowing and air penetration. The feed-out face should be kept smooth and undisturbed – using a shear grab or facer rather than a bucket that loosens the face and opens fissures deep into the silage mass.

Resealing and monitoring 🔗

When silage feeding is paused for an extended period, the silo must be resealed to prevent compounding spoilage losses. Areas in the silo where spoilage has occurred consistently in previous seasons should be noted and the structural issues causing them addressed before the next filling. Monitoring should extend to checking total mixed ration (TMR) temperatures in the feed bunk after delivery – elevated bunk temperatures are a reliable early indicator of aerobic instability reaching the feed.

Moisture and temperature management 🔗

The USDA recommends maintaining silage moisture levels between 45-65% – a range that prevents both microbial spoilage and the risk of spontaneous combustion in drier material. Above 65% moisture, expressed juice can leach nutrients from tower silos, while below 40% moisture, forage does not compact adequately and becomes susceptible to aerobic deterioration. Temperature fluctuations during storage accelerate the activity of spoilage organisms, so siting silos to avoid direct, prolonged sun exposure and maintaining structural integrity to limit heat exchange are worth accounting for in farm planning.

Hygiene and pathogen exclusion 🔗

Before refilling any silage structure, all remaining feed should be removed, particularly any spoiled material. Acids from fermentation can corrode concrete and metal components, so surfaces should be cleaned and inspected for damage before each new fill. Crops intended for ensiling should not be harvested from fields recently spread with manure, as soil and manure contamination is a primary entry route for butyric acid-producing bacteria and other pathogens into the silage mass.

What do you think? Given that spoiled silage cannot be rehabilitated and must be discarded entirely, how would you prioritize the spoilage prevention measures covered here – would you focus first on the ensiling phase or the feed-out phase, and why? And considering that both biological inoculants and chemical additives have distinct trade-offs, what factors on a typical livestock farm would most influence your choice between them?

References

1. https://cropsandsoils.extension.wisc.edu/silage-storage-maintenance-are-you-really-ready-for-spring/
2. https://hayandforage.com/article-permalink-3556.html
3. https://benisonmedia.com/preventive-measures-to-control-silage-spoilage/
4. https://www.agproud.com/articles/61142-silage-pile-top-layer-silage-or-compost
5. https://extension.psu.edu/from-harvest-to-feed-understanding-silage-management
6. https://fyi.extension.wisc.edu/forage/preventing-silage-storage-losses/
7. https://cropsandsoils.extension.wisc.edu/articles/microbial-inoculants-for-silage/
8. https://fyi.extension.wisc.edu/forage/silage-inoculants-what-the-research-tells-us-about-when-and-how-to-use-them/
9. https://www.journalofdairyscience.org/article/S0022-0302(18)30322-9/fulltext
10. https://www.fwi.co.uk/livestock/livestock-feed-nutrition/guide-choosing-using-silage-additives
11. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/silage-additives
12. https://blog-crop-news.extension.umn.edu/2020/01/dont-get-robbed-by-hay-and-silage.html
13. https://silo-pros.com/blog/silo-fires-causes-and-prevention-strategies/