Looking to fine-tune your corn silage production process? A fermentation analysis can unlock clues. When you open a new bag or bunker, running a fermentation analysis will provide a “report card” on your harvest and storage, identifying potential areas for improvement.

How to sample for silage fermentation analysis

Silage samples can be taken as early as six weeks after ensiling, since silage reaches its final low pH around that time. When sampling from a bag or bunker, be sure to get a representative sample of the whole face. Take silage from the top, bottom, sides and middle, and mix together. Avoid fringe samples where water may have entered.

If your silage is stored in an upright silo, run at least the amount needed for a feeding into an empty feed cart, mix it well and retrieve a sample. This will help minimize potential differences in moisture or particle size at different points on the silo surface.

The sample should contain at least 1 quart of silage but no more than 1 gallon. Pack it tightly into a zip-close freezer bag and remove all of the air. It’s a good idea to double- bag the sample to minimize moisture and fermentation acid loss. Ideally, the sample should be refrigerated or frozen prior to shipping and shipped overnight to a commercial lab. Contact your nutritionist, state university or extension agent to find reputable testing labs in your area.

Analyze the results

A silage fermentation analysis summarizes all factors that contributed to the silage-making process, including moisture, temperature, packing and face management. Use them to benchmark your silage and determine how you can improve your production process.


Here are measurements in a typical silage fermentation analysis, along with troubleshooting tips:

1. Dry matter

The dry matter (DM) of the corn silage sets the stage for and influences total acid, pH and titratable acidity values. Ideally, corn silage DM should be between 32 percent and 37 percent. Here are potential problems:

Too wet: Silage that is less than 30 percent DM may have undergone extended fermentation during storage, converting nutrients to acids. Extended fermentation reduces the nutrient value of the forage and results in greater quantities of amines and acids that might depress intake.

Too dry: Corn silage with more than 37 percent DM may have undergone incomplete fermentation. It often contains fewer nutrients due to slower fermentation and lower acid contents. Because you cannot pack very dry silage as densely as wetter silage, there also is greater potential for oxygen to penetrate the exposed silage surface. This allows yeast and mold growth, increasing spoilage.

2. Total acids

When making silage, the goal is to reduce oxygen and increase acidity rapidly so lactic acid bacteria can grow to stabilize and preserve the silage. Total acids should be less than 10 percent of the forage DM. Of the primary silage acids, lactic acid should be the highest (4 percent to 7 percent DM), followed by acetic acid (2 percent to 3 percent DM), propionic acid (less than 0.5 percent) and butyric acid (less than 0.1 percent). Ideally there should be very little, if any, butyric acid.

Too wet: Silage that is too wet often undergoes extended fermentation, which results in greater quantities of amines and acids. In this situation, you will see:

  • Total acids higher than 10 percent DM
  • Lactic acid less than 4 percent DM
  • Acetic acid higher than 3 percent DM
  • Propionic acid higher than 0.5 percent DM
  • Butyric acid higher than 0.1 percent DM

Too dry: Silage that is too dry does not have enough total acids to remain stable when re-exposed to oxygen. Here’s what an analysis will show:

  • Total acids much lower than 10 percent DM
  • Lactic acid is the dominant acid when compared with acetic acid
  • Minimal acetic acid
  • Nonexistent propionic acid and butyric acid

3. pH

Corn silage pH should be between 3.7 and 4. Although not the most important measurement, pH should be reviewed in conjunction with other parameters. Here is what pH indicates:

Too wet: If your silage was ensiled too wet, the pH will likely be less than 3.7. However, a low pH is also often observed in wetter forage if plenty of fermentable carbohydrates are present and the forage is packed well.

Too dry: If your pH is greater than 4, your silage was ensiled too dry and/or there were not enough soluble carbohydrates to be converted to acid.

4. Titratable acidity

Titratable acidity takes into consideration all acids present. By itself, titratable acidity is not very valuable, but when combined with pH and individual fermentation acid analysis, it provides a benchmark value that may be used for troubleshooting dry matter intake (DMI) challenges.

Too wet: If the titratable acidity is 10 mill-equivalents per gram (meq/g) of forage or higher, the combined strength of the acids (acetic and propionic) is well above average, which may indicate the silage was ensiled too wet.

Too dry: If the titratable acidity of a corn silage sample is only 5 meq/g, this indicates the silage was ensiled too dry and is dominated by weaker acids. The acid levels aren’t as high as desired, and the silage may spoil faster than you’ll be able to feed it.

Plan ahead

If your fermentation analysis uncovers areas for improvement, begin planning now. Remember to harvest silage at ideal moisture, chop it properly and deliver it to the storage facility quickly. Pack the silage tightly in thin layers and seal it quickly to ensure it is free of oxygen and water. An inoculant may help speed up fermentation and increase effectiveness of fermentation for silages that do not ferment easily or don’t contain adequate sugars and starches at harvest. A stressed crop will likely benefit from an inoculant.

High-quality corn silage, fed to healthy cows, leads to increased milk production and improves your bottom line. Plan now to ensure you harvest the highest quality silage. PD

References omitted due to space but are available upon request by sending an email to editor@progressivedairy.com .

Phil Krueger