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 the growth of spoilage microbes like clostridia, yeasts and moulds. Yet, pH also can be too low.
The perfect silage pH varies depending on the:
- Forage to be ensiled
- Dry matter (DM) level of the crop
- Phase of ensiling
While there are target ranges, pH isn’t an absolute parameter and is dependent on the mixture of acids produced, which can be influenced by the type of inoculant used.
A fast, efficient front-end fermentation during early ensiling will:
- Reduce the pH of the forage
- Stabilize the silage environment
- Reduce yeast growth, which is the major cause of silage heating
A fast pH drop (to below 5) is essential to reduce DM and nutrient losses and prevent bad fermentations. }
How pH Changes
Prior to ensiling, the pH level of the forage generally will be between 5.5 and 6.0. During ensiling, the pH level will drop due to acid production (mainly lactic acid), with the final pH likely being somewhere between 3.7 and 4.7, depending on the factors described above.
A low pH essentially “pickles” the forage and — coupled with an anaerobic environment — helps prevent the growth of spoilage microbes like clostridia, yeasts and moulds.
If pH is outside of these ranges, there are a few likely culprits.
- A high pH can be due to slow fermentation, which can then allow the growth of spoilage microbes.
- If the silage pH is too low, this is usually due to the activity of “wild” lactobacilli that are naturally present in the silage. Often, this results after a slow initial fermentation. A fast, efficient front-end fermentation can help prevent these wild lactobacilli from becoming established.
pH Changes During Feedout
Once silage feedout begins, the pH may rise again as the process of aerobic deterioration begins. This is normally due to the activity of spoilage yeasts, which can use lactic acid as a food source. Specific anti-mycotic acids — such as acetic acid and/or propionic acid—can help prevent this and the associated heating and mould spoilage.
Forage inoculants can help ensure silage hits the correct pH targets and acid profile to promote stability, retain DM and maximize nutrient preservation.