There are two main types of bacteria used in inoculant formulations, depending on the desired outcome:
- Homofermentative lactic acid bacteria (LAB), which convert soluble sugars from the forage into lactic acid. These bacteria are used to speed up the initial fermentation, helping to quickly reach a low pH. Examples include Lactobacillus plantarum or Pediococcus acidilactici, Enterococcus faecium and Lactobacillus salivarius.
- Heterofermentative bacteria produce acids with strong antifungal properties, such as acetic acid and propionic acid. They can improve silage aerobic stability and help reduce the risks of aerobic spoilage after opening. Examples include the strains Lactobacillus buchneri and Propionibacterium acidipropionici. Other strains such as L. hilgardii are being studied as well.
A forage inoculant product may contain one or more strains of homofermentative, heterofermentative, or a combination of microorganisms.
The formula must be adapted depending on the type of crop, the dry matter (DM) at harvest, the forage sugar content and the protein and mineral content of the forage — among other factors. In addition, LAB may also be combined with enzymes, which can help improve fiber digestibility and fuel the forage inoculant bacteria.
Before choosing a forage inoculant, keep the following criteria in mind.
- Overall objectives: The formula must be selected to the operation’s specific objectives, including the type of crop and dry matter (DM) at harvest — among others.
- Product approval: The product must be approved in the country of use.
- Data to support claims: The manufacturer should provide data for the specific product in the target crop. Ideally, the research should be conducted at independent research facilities to verify the claims. Any trials should validate the inoculant used at the application rate on the product label.
- Strain specificity: Each strain has its own genetic identity and commercial strains are registered with unique strain numbers, for example L. buchneri NCIMB 40788. Strains from one company to the next cannot be expected to perform in the same way.
- Production quality: Forage inoculants should be produced and packaged under accredited manufacturing conditions. For an inside look at how forage inoculants are produced, watch this video.
- Product packaging: Inoculants contain dried viable products that are sensitive to heat, moisture and air. Packaging must be designed to prevent exposure to these elements. The use of high-barrier foils is one common approach.
- Shelf life and storage conditions: Store the inoculant according to indications on the product packaging to preserve the product’s integrity.
- Suitability of product form: Dry granular application may be easier but is less effective than liquid application as crop DM increases.
- Product technology in the application tank or hopper: Over time, bacteria viability after dilution is dependent on the formulation and technology. The product should stay in suspension after dilution to prevent uneven application.
- Technical support: Look for manufacturers that provide product support should any challenges be encountered.
The product label should clearly contain the concentration of LAB, the identity of active substance(s), official approval, precautions for use, stability, date of manufacture, batch number and net weight. Shelf life and storage conditions should be listed.
If the product contains enzymes, guaranteed levels should be declared, and they should be the same as those used in trials to validate product efficacy. If no guarantee levels are given for enzymes, it’s best to consider they are not present.
Example of a U.S. forage inoculant product label and key components:
Colony Forming Units (CFUs)
Microorganisms are very small and difficult to count individually. The bacteria count is expressed as CFU (Colony Forming Units) per gram of fresh forage treated or per gram of product. The CFU represents the number of live and active bacteria. Rates for organisms in spoilage inhibitors vary.