Good Bugs vs Bad Bugs in Silage: Winning the Microbial War in Your Grass Silage

When it comes to making high-quality grass silage, it’s not just about how you mow, wilt, and pack — it’s also about what happens microscopically. That’s right — inside every pit and bale of grass silage, there’s a microbial war going on. And your silage quality depends entirely on which side wins.

In this edition of Precision Microbes Silage Sessions, Ryan Duffy breaks down the battle between good microbes and bad microbes, and explains how Irish farmers can take control of the silage fermentation process to produce more nutritious, palatable, and stable silage.

Fermentation: More Than Just Storage

Silage making is not simply storing grass — it’s initiating a complex microbial fermentation process. This involves thousands of microbes interacting with the forage, sugars, moisture, and oxygen levels. Unfortunately, not all of them are friendly.

Two Teams in the Clamp:

• ✅ Good Bugs: Lactic Acid Bacteria (LAB)
• ❌ Bad Bugs: Clostridial species, Enterobacterial species, Fungi

Understanding who these players are — and how to promote the good ones — is essential to ensuring your animals are getting the best nutrition possible from your silage.

The Good Guys: Lactic Acid Bacteria (LAB)

Lactic Acid Bacteria (LAB) are the heroes of silage fermentation. Their job is to:

• Convert grass sugars like glucose and fructose into lactic acid
• Rapidly drop the pH to 3.8-4.2, creating an acidic environment
• Preserve nutrients, including crude protein and metabolisable energy
• Stop bad bugs from growing

High levels of LAB can lead to:

• Ideal silage fermentation and preservation
• Retention of high feed value
• Optimal palatability
• Reduced risk of spoilage

💡 Remember: faster fermentation = better preservation.

Precision Microbes Silage Additive is a liquid, ready-to-use (RTU) formulation containing live bacterial agents, specifically lactic acid forming bacteria (LAB) and homofermentative bacterial populations. Designed for efficient crop preservation, it promotes a rapid pH drop in both clamps and bales, ensuring high-quality silage. The product is organic certified and can be applied using either ultra-low dosing or standard dosing methods, offering flexibility and ease of use for farmers aiming to enhance silage fermentation and nutrient retention.

The Bad Guys: Clostridia, Enterobacteria, and More

On the other side of the microbial battlefield are harmful organisms that can spoil your silage, waste valuable nutrients, and reduce animal performance.

❌ Clostridial Species

In terms of silage fermentation Clostridial species fall into two main categories: (i) Saccharolytic varieties and (ii) Proteolytic varieties. Saccharolytic clostridial species utilise any lactic acid produced within grass silage clamps and bales (and any residual water-soluble carbohydrates) and convert it into the undesirable butyric acid. This includes species such as Clostridium Butyricum and Clostridium Tyrobutyricum. Proteolytic clostridial species are responsible for the degradation of the crop’s crude protein, or more specifically, the amino acids. These reactions create acetic acid, butyric acid, ammonia, and amines. Examples include Clostridium Bifermentans and Clostridium Sporogenes.

• Degrade valuable lactic acid to produce butyric acid, a foul-smelling, unpalatable by-product
• Break down crude protein into ammonia and amines (compromises gut health)
• Thrive in dark, wet, foul-smelling forage

Where do they come from?

• Soil contamination — often from muddy conditions or poor harvesting techniques
• High ash content in your silage (check your forage analysis — >8% ash is a red flag)

🛠️ Minimise soil contamination by harvesting in dry conditions, using sharp and correctly set blades, tethers and rakes, and keeping machinery clean.

❌ Enterobacteria Species (e.g., E. coli)

• Often introduced through slurry contamination
• Direct competition with LAB for simple sugars
• Produce dark, wet silage with lower nutritive value

How to reduce enterobacteria?

• Apply slurry only when grass has recently been mown (i.e., short stubble)
• Allow for sunlight exposure — UV rays help kill bacteria
• Avoid heavy slurry applications close to cutting

How to Tip the Balance in Favour of the Good Bugs

There’s good news — with a few smart management steps, you can help the good microbes win and keep the bad ones at bay.

1. Harvest During Dry, Sunny Weather

• Dry conditions reduce the risks of soil contamination
• Increases sugar content in grass, especially if cutting in the afternoon

2. Wilt for 24 Hours (If Conditions Allow)

• Brings dry matter to the target range (target 28–32%)
• Makes conditions less favourable for bad bugs

3. Rapid Ensiling & Tight Sealing

• The faster you fill and seal your pit or wrap your bales, the faster LAB can start fermenting
• Oxygen exposure gives yeasts and moulds a chance to grow — so keep it out!

4. Use a Proven Silage Additive

• Additives containing homo-fermentative lactic acid bacteria, like those from Precision Microbes, help boost LAB numbers
• Ensures rapid acidification and faster pH drop
• Deactivates bad microbes early in the process

If you’re unsure, a forage analysis can reveal a lot about what’s happening microbially inside your clamp.

Conclusion: Let the Good Bugs Win

Silage isn’t just about what you grow — it’s about how well you preserve it. And the battle between good and bad microbes is real.

To let the good bugs win:

• Cut in dry weather with serviced machinery
• Wilt for 24 hours if possible
• Keep oxygen out at all costs
• Use a homofermentative LAB additive to support rapid fermentation

The result? Preserved silage, retained nutrition, maximum palatability. This will keep your animals healthy and productive through the winter months. Getting fermentation right protects what you’ve grown, reduces dependency on bought-in feeds, and supports better productivity from your animals.