Choosing the best inoculant depends on your silage goals. Inoculants can shift silage fermentation toward better crop preservation by using lactic-acid bacteria in the inoculant to overwhelm the natural lactic-acid bacteria on the crop.
Homo-Fermenters vs. Hetero-Fermenters
The two main types of silage inoculants include traditional homo-fermenters, such as Lactobacillus plantarum, Pediococcus species and Enterococcus faecium; the other main type is the hetero-fermentative bacteria Lactobacillus buchneri (L. buchneri). Homo-fermenters convert 6-carbon sugars into one product, lactic acid. In contrast, hetero-fermenters produce multiple products.
Key attributes of these fermentation products are:
- Lactic acid is a strong acid, weak spoilage inhibitor and is fermented by rumen bacteria.
- Acetic acid is a weak acid, good spoilage inhibitor and is unfermented in the rumen.
- Ethanol is neutral, a poor spoilage inhibitor and is partially fermented in the rumen.
- Carbon dioxide is lost dry matter.
Thus, if preserving crop quality is your primary goal, use a homo-fermenter. If minimizing heating is your primary goal, use a hetero-fermenter.
Homo-fermentative inoculants have often lowered silage pH, but not always, and they’ve lowered pH in hay-crop more often than whole-grain silages. Lowered pH was achieved 58% of the time with alfalfa trials, 63% with grass silages, 43% with corn silages and 31% with small-grain silage trials. Dry matter recovery was improved by ~6% in 38% of trials, or by 2% to 3% averaged over all trials. On average, 3% to 5% increases in intake occurred in 27% of research trials, weight gain in 52%, and in milk production in 46% of research trials. Bunk life/aerobic stability were improved in 28% of trials but reduced in 31% of trials; changes were generally positive in hay-crop silages and negative in corn silages and small-grain silages, but small regardless.
A solution to bunk-life issues with whole-grain silages is L. buchneri. Lab studies with L. buchneri have increased acetic acid and slightly increased pH. Since acetic acid inhibits yeasts and molds, L. buchneri-treated silages have been more aerobically stable than untreated silage. Silages inoculated with L. buchneri have been intermediate in DM recovery compared to untreated silage and homo-fermentative-treated silage, since carbon dioxide is made/lost when acetic acid is produced. In lactation trials with L. buchneri-treated silage, bunk life/aerobic stability has increased consistently. Acetic acid has also increased consistently, more than 5% in several cases. DM intake and milk production by cows has been unaffected by these inoculants.
When are Inoculants Useful?
Positive results are most likely when homo-fermentative inoculants are applied to hay-crop silage with wilting times of ≤1 day and when corn silage is harvested dry, e.g., after a killing frost. Based on limited research, L. buchneri inoculants work across a wide range of conditions.
Wet or Dry Inoculants?
Bacterial inoculants work only if the bacteria are alive when they’re applied, so store them in a cool, dry place. Don’t use chlorinated water to dilute wet inoculants unless the chlorine level is <1 parts per million or the inoculant contains chemicals to take care of the chlorine, as chlorine can’t discriminate between “bad” and “good” bacteria. Choose a wet or dry inoculant based on a) how well you can keep it alive before and while applying, and b) how well you can mix it with the crop.
Homo-fermentative inoculants are best to improve DM recovery and animal performance, particularly with hay-crop silages. For bunk-life/aerobic-stability problems, is it due to a management issue that can be solved without an additive? If not, L. buchneri is a good alternative to propionic acid or anhydrous ammonia as it’s safer to handle, cost competitive and has similar effects on DM recovery and animal performance. L. buchneri is 85% effective on corn silage but is a slow grower that requires 45 to 60 days of storage to be effective, so it’s ineffective for heating problems with immature silage.
By: Richard Muck, U.S. Dairy Forage Research Center, USDA-ARS