Silage pH: Lower is not necessarily better

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A low pH is needed to create stable, high-quality silage. It helps create the environment to essentially “pickle” the forage and — coupled with lack of oxygen — helps prevent growth of spoilage microbes like clostridia, yeasts and molds.

Yet, pH also can be too low. The final pH is usually between 3.7 and 4.7, depending on the forage and the dry matter (DM) of the crop. A pH significantly lower than 3.7 indicates that the final part of the ensiling fermentation may have been dominated by acid-tolerant lactic bacteria and the pH of the feed should be taken into account when designing the ration.

First, samples can be taken around four weeks after ensiling to determine the acidity of silage,  as the initial ensiling fermentation should be completed. The pH may still change after this point, for example, if there is a controlled conversion of lactic acid to acetic, due to the use of an inoculant containing Lactobacillus buchneri (pH may increase a little, since acetic acid is not as acidic as lactic but does have anti-yeast activity).

Lower pH values are typically seen in lower DM silages: the lactic acid bacteria need to produce more acids to pickle the forage — basically a dilution effect due to high moisture. Silage with a low pH should be carefully fed to avoid intake problems and, potentially, acidosis.

A fast, efficient front-end fermentation leads to a quick pH drop and helps prevent other (spoilage) microorganisms from growing. This helps preserve nutrients and DM, stabilize the silage environment and reduce yeast growth, which is the major cause of silage heating.

Forage inoculants can help ensure silage hits the correct pH targets and acid profile to promote stability, retain DM and maximize nutrient preservation. As an example, the homolactic lactic acid bacteria (LAB) Pediococcus pentosaceus 12455, provides an efficient, fast fermentation fueled by sugars generated by high activity enzymes.

In addition, producers need to make sure that fill rate and packing density are optimized, to help with achieving a fast start to the fermentation and reduce the growth of all spoilage organisms.

For additional tips on producing stable, high-quality silage, visit or Ask the Silage Dr. on Twitter or Facebook.


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