Silage pH varies depending on the forage to be ensiled, the dry matter (DM) level of the crop and the phase of ensiling — among other factors. While there are target pH ranges, this measure isn’t an absolute, fail-safe parameter and is somewhat 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 and 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.
In general, the pH level of the forage will be between 5.5 and 6.0 prior to ensiling. 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 previously. A low pH essentially “pickles” the forage and — coupled with an anaerobic environment — helps prevent growth of spoilage microbes like clostridia, yeasts and molds.
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.
Once silage feedout begins, the pH may rise again as the process of aerobic deterioration begins. This is normally due the activity of spoilage yeasts, which can use lactic acid as a food source. To prevent this, and the associated heating and subsequent mold spoilage, we need to produce specific anti-mycotic acids, e.g. acetic acid and/or propionic acid.
Forage inoculants can help ensure silage hits the correct pH targets and acid profile to promote stability, retain DM and maximize nutrient preservation. The lactic acid bacteria (LAB) Pediococcus pentosaceus 12455, provides an efficient, fast fermentation fueled by sugars generated by high activity enzymes. In addition, the high dose rate Lactobacillus buchneri 40788 is the only active bacteria reviewed by the FDA and allowed to claim improved aerobic stability of silages and HMC.