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Keeping silage ‘pickled’

Kelli Boylen for Progressive Forage Published on 11 July 2019
packing silage

“I highly recommend inoculants for everyone. It won’t increase the nutrient content of your silage, but your silage will maintain quality rather than losing it,” says Hugo Ramirez of Iowa State University Extension.

Most inoculants are used to increase lactic acid production, which in turn will preserve forage via anaerobic fermentation. The fermentation of greenchop into silage is carried out by bacteria that produce lactic acid, hence the name lactic acid-producing bacteria (LAB), says Ramirez. Inoculant products have been developed to deliver highly efficient strains of LAB.

A developing plant stores energy in the form of sugars and starch. When ensiled, microbes ferment the sugars, and they produce organic acids that pickle the forage and preserve forage quality. The production of corn silage is the result of anaerobic bacterial fermentation of the forage, which makes it stable as long as it is not exposed to oxygen. Ramirez says there are naturally occurring LAB in greenchop that can carry out fermentation; however, there are other bacteria that also compete for the same sugars. This competition process slows down the action of LAB, which in turn has the potential to lower the nutritional value of the silage. The reason for this is the greenchop is naturally degrading through respiration and being consumed by other microbes. This process stops when LAB produce enough lactic acid to lower the pH to around 4.0 (acidic pH inhibits the growth of microbes and halts further degradation).

Bacterial inoculants contain live LAB that have been selected for their ability to produce lactic acid and speed up the fermentation process so that forage “pickles” faster, preserving more material and nutrients in the silage. Ramirez says use of inoculants can increase dry matter (DM) recovery by 2% to 3%.

The silage that is put up over several days is the base for rations for an entire year. Ramirez says it is important to have the best quality forage to sustain high animal performance, and inoculants can help make that happen. “Fermented forages are the base of dairy nutrition, yet quality and management practices are highly variable,” he says. Inoculants offer some insurance that the quality will be the best it can be.

While lactic acid is the main driver of fermentation, it is also a preferred medium for yeast growth. For this reason, face management during feedout is critical to capitalize on the initial investment on inoculants and harvesting practices. When exposed to oxygen, the yeast activates a “domino effect of degradation,” says Ramirez. When silage is exposed to oxygen at feedout, the yeast starts degrading the lactic acid. This causes the pH to rise and mold growth may begin. Heating then occurs along with DM loss, and the quality of the silage degrades.

Even when silage looks normal, there may be DM loss ongoing due to yeast and heat. Use a thermometer to check temperatures; 3 feet into the pile should be 75-85ºF. Compost thermometers or thermal imaging cameras can be used to measure temperature and determine if heating is occurring. Besides temperature, visual appraisal is also useful to determine where moldy or rotten silage is. Spoiled silage has negative effects on rumen health and should not be fed.  

There are two types of lactic-acid bacteria found in inoculants. Homofermentative bacteria only produce lactic acid and are highly efficient. Heterofermentative bacteria produce more than lactic acid, commonly acetic acid. Heterofermentative bacteria are not as efficient, but Ramirez says they are still effective, particularly when there are problems with heating during feedout.

Homofermentative bacteria result in rapid fermentation and a drop in pH, leading to a smaller percentage of DM loss and greater preservation of energy by preserving sugars and digestible fiber. Even though homofermentative bacteria may not be good mold inhibitors, they produce lactic acid quickly and are highly recommended as inoculant for alfalfa and other legumes. Because these crops are naturally more resistant to changes in pH, the addition of an inoculant will speed up fermentation.

In addition to lactic acid, heterofermentative bacteria produce acetic acid, which is a good mold and yeast inhibitor. The bacterium with more research behind it is Lactobacillus buchneri; forages inoculated with this microorganism typically have extended shelf life or aerobic stability. Therefore, it is recommended in situations where heating problems exist or with high-risk forages that are harvested dryer than normal or transported from different sites. High-moisture corn and small grain silages may benefit from inoculants with L. buchneri as well. 

The bacteria in inoculants become active when rehydrated; thus, it is important to use water that has not been treated with chlorine or that has less than 1 ppm chloride. Ramirez says the hydrated inoculant should never be allowed to go above 85 to 90ºF, and therefore needs to be kept away from tractor engines and other hot equipment. He recommends using an insulated container for application and using frozen water bottles or sealed ice packs to keep inoculants cool. Do not use ice as it will dilute the concentration of bacteria as it melts.

“Bacteria strains are unique; review the claims and the research behind each product,” he says.

Also, follow manufacturer directions for storage, handling and application rates, which typically target 100,000 colony-forming units per gram of fresh forage. “Follow the instructions to a T,” says Ramirez. There is no harm in over-applying the product, but it is a waste of money.

He adds that is it critical to calibrate and maintain applicators prior to harvest.

In addition to using inoculants, Ramirez says another key to quality ensiled forage is packing the forage as much as possible. He recommends 15 pounds of DM per cubic foot as a minimum. “Having the least amount of oxygen is critical,” he says.

Testing for moisture content at least once a week is recommended to adjust and maintain consistent feeding and nutrition, especially when weather events such as heavy rainfall or really hot weather occur. “The key point is to monitor DM, no matter what equipment is used,” he says. Producers have a variety of options for testing moisture – these options vary from a Koster moisture tester, microwave ovens and food dehydrators to very sophisticated handheld NIR equipment.  

He adds, “Post-harvest management can make or break milk production.” Keep an even face to reduce surface area exposure to oxygen; knock down silage from across the face and mix it into a pile to minimize nutrient variation; and monitor dry matter.  end mark

Kelli Boylen is a freelance writer based in northeast Iowa.

PHOTO: Staff photo.

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