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TAYLOR, Wis. - To choose the right silage inoculant for their needs, farmers need to know a bit about bacteria. Richard Muck, an agricultural engineer at the U.S. Dairy Forage Research Center, Madison, Wis., recently tackled that topic.
Speaking at a silage management meeting at Taylor, Wis., Muck said silage inoculants often use lactic acid bacteria to ferment the sugars in a crop and help preserve it.
"The right inoculant can help ensure that the fermentation goes in the direction you want it," Muck said.
But how do you choose the right inoculant? After all, there are two main kinds - homofermenters and heterofermenters - not to mention combinations of those.
Homofermenters are so named because they produce just one by-product when they ferment sugars. By contrast, heterofermenters yield more than one by-product.
Homofermenters produce lactic acid when they ferment a six-carbon sugar. But heterofermenters produce not only lactic acid, but also acetic acid and carbon dioxide. Depending on the strain of bacteria in the inoculant, a homofermenter can also produce ethanol, along with lactic acid and carbon dioxide. Or, it can yield acetic acid and carbon dioxide.
Whichever type of fermentation takes place, the process is mainly done by some strain of Lactobacillus, Muck said. If the inoculant's package says there's Lactobacillus buchneri inside, it's a heterofermenter. But if there's Lactobacillus plantarum inside, for example, it's a homofermenter.
One way to sort through the Latin names is to look at what the various kinds of inoculants do. Homofermenters produce lactic acid. It's a strong acid, but weak at inhibiting spoilage. However, cows can ferment lactic acid in their rumens, meaning it can aid cow performance, Muck said.
By contrast, acetic acid produced by heterofermenters can't be fermented in a cow's rumen. But acetic acid is good at inhibiting feed spoilage.
Ethanol, also a by-product of heterofermenters, is poor at inhibiting feed spoilage, Muck said. And cows can only partially ferment ethanol. Carbon dioxide, another by-product of heterofermenters, results in lost dry matter, Muck said.
That means if farmers want to preserve the quality of the crop, they should use an inoculant whose bacteria produce lactic acid. For that, a homofermenter is in order.
But if the idea is to keep silage from heating, choose an inoculant whose bacteria make acetic acid. That means a heterofermenter should be used.
The kind of feed can play a role in how good a job an inoculant does. Muck said a homofermenter with its high lactic acid production can improve the stability of alfalfa haylage in a feedbunk.
But don't expect that result if the same inoculant is applied to corn silage. With corn silage, heating can take place faster than if the feed was not treated with a homofermenting inoculant.
Muck conducted research on what the types of silage inoculants are expected to do and what they really do. Inoculants don't always live up to their expectations, he told his Jackson County audience.
Homofermenters are expected to lower the pH of the feed. But they don't do that all the time, Muck said.
They're also expected to reduce the amount of dry matter lost during fermentation. That happens, he said, with five to six percent of the dry matter recovered, or not lost.
These homofermenters are also expected to help animals eating the inoculated feed perform better. Research has shown that livestock performs three to five percent better, Muck said.
In the lab, silage treated with three types of homofermenting inoculants were found to produce eight percent more rumen microbes than untreated silage.
Said Muck, "That could support up to four pounds more milk per cow per day."
To see whether that really does happen, forage center researchers fed silage treated with Lactobacillus plantarum to lactating cows. Cows fed the treated silage ate more dry matter per day - 56.9 pounds, compared to 56 pounds.
They made more milk, too - 89.1 pounds, versus 87. 3 pounds per day, compared to cows eating untreated silage. But the fat test of the milk was 0.01 percent lower, and the protein test was 0.03 percent lower.
However, the milk urea nitrogen (MUN) content was lower in milk from cows fed the inoculated silage. For them, MUN was 11.6, versus 12.7 for cows getting untreated silage.
"The 10 percent reduction in MUN indicates better nitrogen utilization by the cows on the inoculated silage, suggesting more rumen microbe production," Muck said.

Return on investment
What does all that mean in terms of dollars and cents? Muck offered an example with two to three percent less dry matter lost by inoculating silage with a homofermenter. Treating 1,000 tons would cost about $1,000, and the feed not lost to spoilage would amount to 25 tons. If each ton of saved feed is worth $60, that's a return of $1.50 for every $1 spent on the inoculant, Muck said.
Things look even better when higher animal performance is factored in. Assume that milk production climbs three pounds per cow, per day, but only half the time. That's an average milk production boost of 1.5 pounds a day.
If milk is worth $16 per hundredweight, the extra milk is worth 24 cents per cow per day. And if a cow eats 60 pounds of the inoculated silage each day, the inoculant ended up costing three cents per cow per day.
Thatis a huge, 8:1 return on investment, Muck said. A dairy producer can reaping $8 in benefits for every dollar spent on inoculant.

Heterofermenter examined
Muck crunched the numbers on a heterofermenter, too. Here, he looked at the return on investment from silage inoculated with Lactobacillus buchneri.
"Thanks to its higher acetic acid content, this inoculant produced very consistent improvement in the feedbunk stability of the silage," Muck said.
He said farmers can expect to lose one to two percent less dry matter by treating silage with L. buchneri, compared to not treating it.
On cow performance, no additional dry matter was eaten. And only one trial showed a milk production increase.
Muck said, "Expect a positive effect only when the silage would have heated without L. buchneri."
Treating 1,000 tons of silage with this heterofermenter would cost roughly $1,500. Fifteen tons less feed would be lost to spoilage.
"If each ton saved is worth $60, dry matter recovery alone won't pay for using the product," Muck said.
That's because there's $900 of benefit, but $1,500 in cost.
Muck suggested not using this type of heterofermenting inoculant if the silage is expected to cool normally. But if the feed is expected to heat, it could pay to use this inoculant.
That's assuming that a cow would eat four fewer pounds of heated silage each day, and that a cow would produce three fewer pounds of milk per day. With milk worth $16, the three pounds of milk are worth 48 cents each day. But the silage eaten is worth 4.5 cents per cow per day. That's roughly a 10:1 return on investment, Muck said.
Muck mentioned a few things dairy farmers might want to keep in mind if they are going to use an inoculant that contains L. buchneri. First, the bacteria grow slowly. It can take 45 to 60 days after application until the product has much of an effect.
"So it's not an answer to heating problems with immature silage," Muck said. "Propionic acid is the best solution for this case."
What if a farmer wants to make a good silage better? In that case, choose a homofermenting inoculant that contains bacteria such as Lactobacillus plantarum, Muck said.
These kinds of inoculants are best at protecting against dry matter loss and boosting cow performance. Muck said they are a good fit for hay silages and high-moisture corn, and they work best when harvest conditions are good and silos are managed very well.
When using a homofermenter on corn silage, remember that their success rate is inconsistent, Muck said. He said these inoculants work best on corn silage that will be fed during cool weather.
Homofermenting inoculants work even better on high-moisture corn, Muck said. Their best use is on high-moisture corn that will be fed during cool weather.
Muck said use silage inoculants designed for the kind of crop - haylage, corn silage, high-moisture corn, and so on. Apply them at the rate specified on the label.
And, said Muck, "Don't be shy about asking for research data - especially independent results - to back up claims."
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