News details


Silage Wholecrop

How to read a forage analysis / PART 2: Fermentation parameters

How to read a forage analysis / PART 2: Fermentation parameters

Regular forage analysis is important to ensure optimal dietary intake. After an overview of the nutritional parameters and target values, let’s focus on the fermentation parameters. These parameters tell us about the fermentation process and are an indicator of forage preservation and quality.

Fermentation Parameters

  • pH: Represents the acidity of the silage. The final desired pH is dependent on the DM of the ensiled forage. During early phase of the ensiling process, a rapid pH fall is desired to inhibit spoilage microorganisms and maximize nutrient preservation.
  • Ammonia (NH3). Represents the amount of protein that has been broken down during fermentation and is an indication of fermentation quality. The lower the NH3 value, the better the fermentation process.
  • Total Fermentation Acids (TFA). The total acids that have been produced during the fermentation process, including desirable and undesirable acids.
  • Lactic Acid (LA). The main, desirable, fermentation acid; A good fermentation generally means that there is a ratio of at least 3:1 of lactic acid to other acids.
  • Acetic Acid (AA). A normal component of silage that is not as efficiently produced as LA.
  • Butyric Acid (BA). An undesirable acid produced during inefficient fermentation. Its presence generally indicates soil contamination, slurry contamination, or low DM coupled with over-compaction. BA negatively impacts palatability and intake.
  • Ethanol. An undesirable product produced by yeast either during the initial stages of fermentation, during storage if air is allowed to enter the bunker, or at feedout as the yeast become active again if feed management is not optimal. Ethanol production results in reduced dry matter, digestibility and energy is often associated with silage heating at feedout.

Target Values for Forage1

Parameter Abbrev. Units Range Target value
        Corn Grass* Alfalfa
pH pH 3.5 – 5.5 <4 3.5 – 5 4.0 – 5.0
Ammonia NH3 g / Kg DM 0 – 10 <0.9 <2 <4
Total Fermentation Acid TFA g / Kg DM 40 – 200 >80 >100 >90
Lactic Acid LA g / Kg DM 40 – 150 >40 50 – 120 40 – 150
Acetic Acid AA g / Kg DM 10 – 40 <30 <30 <40
Butyric Acid BA g / Kg DM 0 – 40 <0.1 <0.1 <0.1
Ethanol   g / Kg DM 0 – 40 <0.1 <0.1 <0.1

* Bale grass silage will have lower values than bunker, bag, or drive over pile.

1Note that target values vary between countries and are not always achievable.