Interpreting Silage Analyses

February 1, 2015

Interpreting Silage Analyses

Fermentation analyses on silage reports are important for assessing silage quality, and provide clues about the silage making process and factors that influenced the quality of the silage such as: plant maturity, crop moisture, ambient temperature, packing effectiveness, silage additive use, face management, relative numbers and kind of microorganisms that control the fermentation process.

Silage dry matter (DM) is mostly composed of sugars, starch, protein, fibre and minerals.  Harvesting crops at ideal moisture levels (25-35% DM) is critical for properly packing pits or stacks and exclusion of oxygen.   Low DM silages may lead to extended fermentations, excessive protein breakdown and elevated acid levels. High DM crops are difficult to pack and tend to be unstable, allowing for yeast and mould growth.

Reducing oxygen is crucial to enable lactic acid bacteria to flourish, stabilise and preserve ensiled forages.  Lactic acid is stronger than the other silage acids, and is responsible for most of the drop in pH, which can be boosted by using homo-fermentative lactic acid bacteria containing inoculants. Depending on the forage, total acids should be less than (<) 10% of silage DM, lactic acid (4-7% DM), acetic (2-3% DM), propionic (<0.5% DM) and butyric (<0.1% DM).

Low lactic acid concentrations may indicate restricted (high DM) or extended (low DM) fermentations.  High acetic acid levels (>3-4% DM) are often observed in silages ensiled at very low DM’s (<25%), and silages high in butyric acid are usually low in lactic acid.

Acetic acid concentrations can be elevated when Lactobacillus buchneri inoculants are applied to address aerobic stability issues due to spoilage when the silage is exposed to oxygen, especially at feed out.  High butyric acid (>0.5% DM) indicates Clostridial fermentations, and silages generally low in nutritive value, with higher NDF levels as many soluble nutrients have been degraded.

Lower pH’s indicate better preserved and more stable silages.  Legume silages tend to have slower declines and higher final pH’s, due to their high buffering capacities compared with maize and grasses.  Elevated pH’s due to restricted fermentations are not always indicative of poor fermentations or poor silages, but silages with restricted fermentations tend to be unstable when exposed to air.

(Article adapted from Chr. Hansen)

As featured in NZ Dairy Farmer

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