Inoculants are silage additives with a main ingredient of lactic acid bacteria. These bacteria ferment sugars in the crop and help to preserve it. “Adding lactic acid bacteria helps ensure the fermentation goes the direction we want it to go,” said Richard E. Muck at the Midwest Forage Symposium earlier this year.
The researcher from the U.S. Dairy Forage Research Center in Wisconsin went on to explain there are a lot of different inoculant products on the market, but they can be placed in three groups.
1. Traditional homofermentative types: Lactobacillus plantarum, L. casei, Pediococcus species, Enterococcus faecium
2. Heterofermenter: Lactobacillus buchneri
3. Combination types: Homofermenters with L. buchneri
Homofermenters convert sugar into two molecules of lactic acid, while heterofermenters convert the sugar into lactic acid, carbon dioxide and acetic acid or ethanol.
Lactic acid is a strong acid, Muck said. It is a weak spoilage inhibitor but is fermented in the rumen. Acetic acid is a weak acid.
It is a good spoilage inhibitor but is not fermented in the rumen. Ethanol is neutral, a poor spoilage inhibitor and partially fermented in the rumen. Carbon dioxide is simply lost dry matter.
“If you want to preserve the crop quality, put in lactic acid. If you want silage that doesn’t heat, add acetic acid,” he said. “In any case, you want to minimize ethanol and carbon dioxide.”
Homofermentative inoculants should have high lactic acid content, low pH and improved DM recovery, resulting in slightly better animal performance.
In 1997, Muck did a survey to see how well the products worked. Homofermentative inoculants performed better in hay crops than in whole-grain silages.
Inoculants don’t always work because some products may be ineffective or misapplied. It also may be difficult to improve the natural fermentation, particularly in corn silage.
Competition from the natural population can hinder performance. If the inoculant population is less than 10 percent of the natural population it is less likely to work.
Corn silage tends to have a high natural population, whereas alfalfa tends to the low end.
In the same survey, Muck said dry matter recovery improved in 38 percent of the trials, with an average of 2 to 3 percent improvement.
Looking at return on investment, Muck calculated the treatment for 1,000 tons of as-fed silage at $1,000 or $1 per ton.
With a 2 to 3 percent average improved dry matter recovery, that’s 25 as-fed tons saved. A farmer breaks even if each ton saved is worth $40 or more.
Animal performance was shown to improve by 3 to 5 percent when inoculants were effective. Assuming a three-pound milk increase per cow per day when effective and a 50 percent effective rate would yield a 1.5-pound milk increase per cow per day.
If the price of milk is $16 per hundredweight, that’s 24 cents extra income per cow per day. If the cow is eating 60 pounds as-fed silage per day, the cost of the inoculant is three cents per cow per day.
“That’s an eight-to-one return on investment,” Muck said. “You can make money if this product affects animal performance.”
Muck recently set out to answer: How could homofermentative inoculants improve milk production by two to three pounds per cow per day? And, can this be expected from all homofermentative inoculants?
In an in-vitro study, he found some inoculants were producing less gas in the rumen than the control.
Since the main products of fermentation are gases, volatile fatty acids and rumen microbes, if gas production decreased, something else had to increase. Muck learned the population of rumen microorganisms was growing.
Three of the four inoculants were found to produce 8 percent more rumen microbes than the untreated. Since rumen microbes are a major source of protein to the cow that amount could lead to an additional four pounds of milk per cow per day.
Moving into an animal feeding trial, Muck use fourth-cutting alfalfa that had crude protein at 25 percent dry matter and 32 percent NDF.
The alfalfa silage was fed at 50 percent of ration along with corn silage, high-moisture corn and soy hulls. In total, the ration had 16.2 percent crude protein and 27.3 percent NDF.
In comparing the silage with the inoculant to untreated silage, there was no effect on dry matter intake. There was a two-pound increase in milk.
Milk urea nitrogen was down 10 percent, which indicates better protein efficiency with inoculated silage.
From here, Muck would like to confirm that more rumen microbes were produced in the trial, figure out why certain inoculants are causing silages to produce more rumen microbes and to confirm that the in-vitro test really does screen for inoculants that can produce a significant animal response.
Nevertheless, there is sound evidence that some inoculants can increase rumen microbe production, which in turn increases milk production.
“We now have increased confidence that we can expect two to four pounds more milk per cow per day with the use of some inoculants,” Muck said. PD
Karen Lee
Editor
Progressive Dairyman magazine
