By Ray McLaughlin, Account Manager, Novonesis
Over the years, I have been asked about high acetic acid levels in corn silage and the effects on dry matter intake. Acetic acid has strong antifungal properties, so its presence in your silage can help to reduce mold and yeast counts as well as extend the bunk life of your ration. But, in the case of acetic acid, can too much of a good thing be bad? While traditional logic suggests that high levels of acetic acid (the vinegar smell in silage) make feed unpalatable to cows, the use of heterofermentative silage inoculants – specifically those containing Lactobacillus buchneri – tells a different story.
Fermentation quality vs. spoilage
In a “wild” or poorly fermented silage, high acetic acid is usually a byproduct of enterobacteria or clostridia. These “undesirable” microbes don’t just produce acid; they also produce foul-smelling biogenic amines, like cadaverine, due to the breakdown of proteins. It is these malodorous byproducts, rather than the acetic acid itself, that typically drive cows away from the bunk.
When you use a heterofermentative inoculant such as SiloSolve® FC, the acetic acid is produced by beneficial bacteria in a clean, semi-controlled process that doesn’t produce those repulsive secondary metabolites.
One of the biggest drivers of dry matter is feed freshness. High acetic acid acts as a powerful antifungal agent, inhibiting the yeasts and molds that cause silage to heat once exposed to air.
Cooler feed
By preventing aerobic spoilage, heterofermentative inoculants extend the “bunk life” of the feed.
Consistency
Cattle are more likely to maintain high intake when the Total Mixed Ration (TMR) remains cool and stable throughout the day, rather than heating up and becoming less palatable.
Summary of differences
| Feature | High acetic (poor fermentation) | High acetic acid (inoculated with L. buchneri) |
| Origin | Wild bacteria (Enterobacteria and Clostridia during fermentation, or Acetobacter at feedout) | Carefully selected bacteria strains from targeted inoculant |
| Co-products | Ammonia, butyric acid, amines | Lactic acid, 1 -2-propanediol |
| Smell | Putrid, vinegary or “off” | Clean vinegar smell |
| Dry Matter Intake | Often decreased | Maintained |
Following are some possible suggestions for determining whether higher levels of acetic acid are the result of poor fermentation or the consequence of using a heterofermentative silage inoculant:
- Is the higher level of acetic acid also accompanied by higher butyric acid levels? If so, the crop was most likely poorly fermented, could have been put up too wet, and fermentation was driven by Enterobacteria.
- Is the silage poorly packed or feed out rate too slow? Acetobacter species are aerobic bacteria that can contribute to acetic acid production during the aerobic exposure (feedout) phase. While they are generally present in low numbers during the initial anaerobic fermentation, they can proliferate rapidly when the silage is exposed to oxygen.
The elevated acetic acid from a heterofermentative inoculant such as SiloSolve® FC is a preservative, not a byproduct of spoilage organisms. By keeping the silage “aerobically stable,” “cool” and free from spoilage organisms, the inoculant ensures the feed remains appetizing from the silo to the feed bunk and helps to maximize feed intake.