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Silage inoculants: When and how to use them

Richard Muck
U.S. Dairy Forage Research Center, USDA-Agricultural Research Service
January 28, 2012

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:

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-Fermenter Research

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.

Hetero-Fermenter Research

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.

Summary Points

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.

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