Funky fermentations: A case study – Jon Urness, Vita Plus
One of the most frustrating aspects of putting up good forage is when everything seems to have been completed correctly and yet the fermentation analysis shows a volatile fatty acid (VFA) profile that is far from perfect.
We share producers’ frustrations when this happens. Those calls usually start with something like this: “Shouldn’t lactic acid be higher than acetic acid in a corn silage VFA analysis?” or “How much acetic acid is too much?”
Case study: What happened here?
Let’s pick this one apart a little. This was an actual case and proved to be very puzzling at first. The analysis results are shown below.
An ideal lactic-to-acetic ratio is 2-to-1, or even a bit higher, and we don’t typically see acetic acid above 2 to 3 percent. In fact, according to our own Vita Plus forage scorecarding program, ideal lactic acid is 4 to 7 percent, acetic acid is 1 to 3 percent, and the ratio of the two should be 3-to-1 (lactic-to-acetic) or higher. It’s no wonder the producer had concerns with acetic acid consistently running higher than lactic acid, and acetic acid levels far exceeding what is normally considered ideal.
The dairy owners were obviously concerned, but not in a panic because intakes were very good and corresponded to their milk production in the mid-90-pound range.
The investigation began with a conversation about moisture. It’s well known that very high moisture corn silage (more than 70 percent moisture) can cause high acetic acid production, but even though the above data shows a trend toward higher acetic acid, the corn silage was put up with ideal moisture in the 62-to-66-percent range. Scratch that cause.
The owners of this dairy take great pride in harvesting at the right moisture, their kernel processing score, and keeping plenty of inventory on hand so new corn silage does not have to be fed for at least six months after harvest. We contacted Dr. Limin Kung Jr., University of Delaware. He agreed these acetic acid values are pretty high and commented that, if silage has been in the silo for more than one and a half years, natural L. buchneri tends to take over and acetic acid can increase. However, slightly higher acetic acid production is a small price to pay for assurance that well-fermented corn silage is always being fed. Plus, the levels found on this farm cannot be attributed solely to extended storage time. Kung also theorized that highly processed corn silage could favor higher acetic acid production, but, once again, not to the extent shown in these samples.
Other possible sources
It didn’t take long to flesh out inoculant treatment or naturally occurring bacteria as a possible source of high acetic acid in this silage. This corn silage was treated with Crop-N-Rich® Buchneri inoculant, but our experience with L. buchneri does not confirm that very high acetic acid is associated with application. We looked at other similarly treated VFA samples from other farms and found that a more typical result is 5.85 percent lactic acid and 2.15 percent acetic acid – almost the perfect 3-to-1 ratio. We ruled out the possibility of over-application because the chopper operators are meticulous about application.
Next, we briefed Dr. Richard Muck, a research agricultural engineer at the USDA Dairy Forage Research Center, on this puzzling finding.
Muck noted, “I have occasionally seen L. buchneri-treated silages with high acetic acid on the order of what we see here. When you have 550-day old silage in the bunker, there is plenty of opportunity for L. buchneri to do its job, which is why acetic acid is so high. I have yet to see high acetic acid produced by buchneri result in reduced intake or milk production.”
While Muck doesn’t look to supplemental L. buchneri as the cause of high acetic acid in this case, he does suggest that Clostridia or enterobacteria could have the same effect. However, when that occurs, intakes and milk production typically also suffer. Because that’s not happening on this dairy, that is not likely the cause.
Instead, we reached the conclusion that the combination of prolonged storage time (550 days) and L. buchneri (either supplemental or naturally occurring) may have resulted in higher than normal acetic acid levels. However, in contrast to a wild acetic acid fermentation, caused by enterobacteria or acetobacteria, this controlled L. buchneri fermentation did not result in a decrease in intakes or milk production. In fact, the feed was extremely stable, and the only negative result was a higher-than-ideal acetic acid level on paper.
Thus, if a lab analysis reveals acid levels that seem out of line, contact your nutritionist and start with a look at your cows’ intakes and milk production. That’s an important piece of the puzzle when trying to uncover the source of a funky fermentation.
Feed quality and nutrition
Forage storage and management