Microbial inoculants are an important part of the silage process and have been used for decades to create a more efficient fermentation process. The key to inoculant effectiveness is proper management.

Silage inoculants are generally classified into two broad categories. First, classical homolactic acid-based inoculants are used to speed up the ensiling process and make silage fermentation more efficient, which hopefully results in improved recovery of dry matter and energy.

“The rapid decrease in pH caused by these inoculants can inhibit unwanted bacteria, like clostridia and enterobacteria, and can also limit protein degradation during the ensiling process, especially in legume silages,” said Limin Kung Jr., Ph.D., professor at the University of Delaware. “This category is made up of organisms like Pediococcus acidilactici, Pediococcus pentosaceus and Lactobacillus plantarum.”

The second silage inoculant category consists of additives based upon using the organism L. buchneri. This group of inoculants is designed to improve the aerobic stability of silages by inhibiting yeasts.

“Some producers utilize a combination of the two types of inoculants. On the front end, they use the homolactic acid product to speed up fermentation and dry matter recovery, and then L. buchneri improves the aerobic stability on the back end of the process,” he said. 

Strain Selection

Bacteria can be identified by genus, species and strain.  For example:

Lactobacillus (genus) plantarum (species) MTD1 (specific strain) 

If the label only states L. plantarum and doesn’t designate strain, it’s unclear what kind of results to expect. 

“All Holstein cows are not the same; some produce more milk and some less. Similarly, bacteria with the same genus and species names (e.g., L. plantarum) cannot be assumed to be exactly the same either,” said Kung. “Knowing the strain of your inoculant can be important because you can seek out published research data that independently supports the use of a specific organism.”  

For homolactic acid based inoculants, the organism L. plantarum MTD1 likely has the most published research of all L. plantarum strains, supporting its efficacy, he said.  For inoculants that improve aerobic stability, the organism L. buchneri 40788 is the most highly researched of the L. buchneri strains.  ​ 

“This doesn't mean other strains of L. plantarum or L. buchneri are not as good,” he said. “It just means that one should be cautious using a strain of any bacteria that is not supported by a significant amount of research.” 

Factors Affecting Efficacy

The efficacy of an inoculant is driven by several factors. 

The inoculant must be applied uniformly at the correct application rate onto the crop. Inoculant bacteria cannot "self-distribute" themselves evenly throughout the silo. 

“Microbial inoculants can be applied with low-volume applicators at the chopper to provide a more even distribution of the inoculant, using just a few ounces of water for every ton of forage,” he said. 

When using a water-applied inoculant, do not allow the water-inoculant mix to reach temperatures above 95°F to 100°F.  Temperatures higher than this will cause the death of bacteria in the tank.

The water-inoculant mixture is stable for about 48 hours, so any unused solution should be discarded after three days. 

High levels of chlorine or peroxide in water can impact microbial inoculants, as bacteria is very sensitive to both. Never mix inoculants in hot water.