Silage inoculants: When and how to use them
Silage inoculants work by shifting silage fermentation toward better crop preservation. That happens when lactic-acid bacteria in the inoculant overwhelm the natural lactic-acid bacteria on the crop. However, even the best inoculants are not always successful.
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; and more recently the hetero-fermentative bacteria Lactobacillus buchneri. Homo-fermenters convert 6-carbon sugars into one product, lactic acid. In contrast, hetero-fermenters produce multiple products. For example, they may convert 6-carbon sugar into a) lactic acid, acetic acid, and carbon dioxide; or b) lactic acid, carbon dioxide, and ethanol; or convert lactic acid into acetic acid and carbon dioxide.
Key attributes of these fermentation products are:
- Lactic acid is a strong acid, weak spoilage inhibitor, and fermented by rumen bacteria.
- Acetic acid is a weak acid, good spoilage inhibitor, and unfermented in the rumen.
- Ethanol is neutral, a poor spoilage inhibitor, and partially fermented in the rumen.
- Carbon dioxide is lost dry matter.
Thus, the best inoculant depends on your goals. If preserving crop quality is your primary goal, use a homo-fermenter that maximizes lactic acid production. If minimizing heating is your primary goal, use a hetero-fermenter (L. buchneri) that produces acetic acid.
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- and small-grain silages, but small regardless.
A recent solution to bunk-life issues with whole-grain silages is the hetero-fermentative 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. However, DM intake and milk production by cows has been unaffected by these inoculants.
Research Combining Homo- and Hetero-fermenters
Several small-scale studies have results consistent with L. buchneri for aerobic stability, fermentation products, and pH. Cow-trials are in progress.
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 ppm 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 a slow grower that requires 45 to 60 days of storage to be effective; so it's ineffective for heating problems with immature silage.