Using an inoculant can offer a return on investment given the right situation, the right crop, and the right inoculant.
“There are two areas where you get a return on investment – dry matter recovery and animal performance,” said Richard Muck, agricultural engineer with the U.S. Dairy Forage Research Center, Madison, Wis., part of the Agricultural Research Service of the USDA.
A good inoculant helps ensure that fermentation happens quickly and goes in the direction you want, he said.
What is an inoculant?
In the dairy silage business, inoculants refer to silage additives that mainly contain lactic acid bacteria. This group of bacteria ferments sugars in the crop and helps to preserve it.
There are two main types of lactic acid inoculants. The traditional homofermentative types include Lactobacillus plantarum, L. casei, Pediococcus species and Enterococcus faecium.
As one six-carbon sugar molecule is fermented by a homofermentative inoculant, it is changed into two lactic acid molecules.
A heterofermenter, Lactobacillus buchneri, turns the six carbon sugar molecule into one lactic acid plus one acetic acid molecule, plus carbon dioxide.
In other cases, the heterofermenter will produce one lactic acid plus one ethanol molecule and carbon dioxide. L. buchneri can also turn one lactic acid molecule into one acetic acid plus carbon dioxide.
End product comparison
Lactic acid is a strong acid that helps reduce the pH of the harvested material.
“It has one downside,” Muck said. “It is not a very good spoilage inhibitor. It doesn’t do a good job of inhibiting yeasts and molds.”
When silage, inoculated with a homofermentative inoculant, is exposed to oxygen, stability may be diminished in some cases and the product may heat up sooner.
Acetic acid is a good spoilage inhibitor, but it is not a very strong acid.
“It’s not going to take the pH down below 4.5, and it is an end product of fermentation in the rumen, so the rumen microorganisms cannot use the acetic acid,” he said. “It’s energy to the cow, but it’s not energy to the rumen microorganisms.”
Ethanol and carbon dioxide that can be produced by a heterofermenter are best avoided, he added.
Alfalfa/grass vs. corn and small grains
Muck said the homofermentative inoculants work well in alfalfa and grass silage. These inoculants are less successful in corn or small grains.
“Corn silage is really high in lactic acid normally, and low in acetic acid. So if we have good fermentation, it’s hard to improve on it,” he said.
When a feedstuff has a lot of natural inoculum, an added inoculum cannot overwhelm and change silage fermentation much. This is more often the case with corn than alfalfa.
On average, homofermentative inoculants can offer a 2 or 3 percent dry matter recovery improvement.
“The big surprise is only a quarter of trials show improved feed intake by dairy cows, but half of the trials are showing improvement in gain and growing animals,” Muck said. “Half of the time, the lactation studies show improvement in milk production in the range of 3-5 percent.
“This is way more than you would project from what we have seen happening in the silo.”
Return on investment for homofermentative inoculants
Muck discussed two ways that dairy producers receive a return on investment from using homofermentative inoculants. This includes dry matter recovery and animal performance.
If the inoculated silage offers a 2-3 percent improvement in dry matter recovery over silage that is not inoculated, then dry matter recovery alone can pay for the product.
As an example, if the farmer treats 1,000 tons, and spends $1,000 on inoculant, the product offers a breakeven if the farmer saves 25 tons of feed valued at $40 per ton.
The reward comes if milk performance is improved by 3-5 percent.
Muck suggested that the dairy cow could provide an extra three pounds of milk per day when a good quality inoculated silage is fed.
Even if the inoculated silage were effective 50 percent of the time, milk production would be increased by 1.5 pounds per day.
Given a milk price of $10 per hundredweight, this scenario suggests an extra 15 cents income per cow per day.
If the dairy cow eats 60 pounds of silage per day, then the inoculant cost is about 3 cents per cow per day.
“You can see this type of product does pay for itself, particularly from the animal performance side,” said Muck.
Return on investment for heterofermentive inoculants
“These products are typically more expensive,” Muck said.
A heterofermentive inoculant, like L. buchneri, offers 1-2 percent on average dry matter recovery over silage that is not inoculated.
Generally it costs $1.50 to treat one ton, or $1,500 to treat 1,000 tons.
“If each ton saved is worth $40, dry matter recovery alone won’t pay for using the product, as a $600 benefit cost $1,500,” he said. “You’re going to need an improvement in animal performance.”
If the heterofermentive inoculant keeps the silage from heating, that is a benefit.
If the producer is able to avoid a reduction of 4 pounds of dry matter intake in the TMR, and avoid a 3-pound per day drop in milk production, then the inoculant does pay.
An avoidance of heating gives 30 cents more milk income per cow per day with a $10 per hundredweight milk price – at a cost of 4.5 cents per cow per day.
“You can see under these assumptions, the heterofermentive product does pay for itself when avoiding a heating situation,” Muck said. “That certainly can happen with corn silage in the summer.
“You can do very good management and still have a heating situation.”
While there is a large expectation for great success with combination inoculants, Muck said it is still too early to tell how well these products work.
There are several published small-scale studies, but large-scale field trials still need to be completed, he said.
The combination inoculants are about twice as expensive as the standard homofermentive inoculants.
The dairy producer would need to see a significant increase in milk production to see a return on investment for combination inoculants.
“I think there is a lot of potential there, but I am a little hesitant to say combination inoculants are the way to go. There just aren’t animal trials out there outside of company literature,” Muck said. “There is potential there, but I will feel a lot better when I see published literature on some of those studies – just to make sure they are improving animal performance.”