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Inoculants: The dairy farmer’s dilemma

Bill Powel-Smith Published on 06 May 2015

men looking at feed

Every inoculant comes with a salesperson who professes how great their product works and how much their inoculant will save the producer money by reducing shrink and preserving feed quality.



In response, the producer mutters, “I wish there was a way to tell if it’s really working. How do I know if your inoculant, or anyone else’s, is doing anything?”

Now we can demonstrate the role inoculants play in maintaining year-round, high-quality fermented forage available to feed your cows. Inoculant choice, however, is just one part of a group of key decisions producers make when putting up forage. Let’s look at how inoculant choice and performance dovetails with decisions on plant harvest moisture, chop length, packing and covering.

Inoculants lower pH quickly

Fermentation is the lowering of pH to a stable point of 4.5 in haylage and 4 in silage. Bacterial inoculants feed on sugars and produce acids that lower the pH. These types of inoculants provide high numbers of lactic acid bacteria that quickly multiply in the forage mass.Natural levels of lactic acid bacteria coming into the silos on the plants can take twice as long or more to lower the pH to a stable point.

These lactic acid bacteria found on the forage at the time of chopping consume oxygen and convert the sugars into acid, primarily lactic acid and some acetic acid, depending on their genus and species. The longer the process of fermentation takes, the more heat produced, sugars and starches consumed, and proteins broken down to ammonia.

Inoculants that contain lactic acid bacteria such as L. plantarum, L. casei, Enterococcus faecium and Pediococcus species will increase the rate of fermentation during the initial fermentation process, which ensures that terminal pH is reached as soon as possible.


Fermentation failures

Fermentation failures occur in areas where too much oxygen is available and the process of pH lowering slows or stops. This happens because the aerobic (oxygen-loving) bacteria are allowed to grow unchecked and dominate the lactic acid bacteria.

Higher porosity areas, often near the outer rim of structures, will show mold or spoilage. In other situations, when water dilutes the fermenting acids, layers or areas of spoiled feed inside the feed structure can be created.

When fermented feed is re-exposed to oxygen during facing and feedout, the dormant yeasts will begin feeding on the lactic acid, raise the pH of the feed and allow the “decomposition micro-organisms” (including molds) to begin breaking down the feed. We can measure this activity with heat probes since heating is one of the byproducts of decomposition (think of composting).

The power of inoculants

Inoculants with high-qualityL. buchneri bacteria can minimize the need for TMR heating stabilizers, even during the hot days of summer.

Superior inoculants will delay heating for an extended time, which allows producers to feed cool feed. Less effective inoculants allow feed to heat and spoil within hours, a possibility that can be easily monitored on the farm.

An ideal inoculant will contain a combination of lactic acid bacteria strains that improve the rate of fermentation on the front end and other lactic acid bacteria strains that reduce heating during feedout. Superior inoculants contain multiple strains of lactic acid bacteria that can address these diverse tasks.


Three critical decisions

Armed with this basic knowledge about fermentation, let’s see how three other critical decisions can impact the stability, quantity and quality of the forage being stored for feeding.

The first critical decision concerns the moisture level of the feed going into storage. The optimum range for corn silage is 32 to 38 percent dry matter. Silage that is wetter than 32 percent dry matter (over 68 percent moisture) will take longer to reach terminal pH and thus consume more sugars and starches.

Wetter silage can be 15 to 20ºF warmer than silage in the same structure at 32 to 38 percent dry matter. Silage drier than 38 percent dry matter is at risk of being too porous, which may result in the molding and spoilage commonly visible near the outer rim of many feed structures and piles.

The optimum dry matter range for haylage is 35 to 50 percent. Haylage wetter than 35 percent dry matter can create an environment favorable to clostridial bacterial growth, which is problematic for cows. Haylage drier than 50 percent is very porous and can be a source of molding.

The second critical harvest decision is chop length and degree of processing. Finer chop length, tight kernel processing and some of the newer shredding techniques can all improve packing ability and reduce porosity – even on silage drier than 38 percent.

Haylage drier than 45 percent dry matter should be stored deeper into the structure, and feed that is between 35 to 40 percent dry matter should be placed on the outer 30 inches of the structure because it’s less porous and less apt to mold.

The third critical harvest decision is packing and density levels. On piles and bunkers that get filled and shaped with tractor blades and packing equipment, a good strategy is to lay down forage in 6-inch layers. Feed packed in layers thicker than 6 inches will have significantly lower densities.

In pre-harvest planning for proper packing, the rule of thumb for equipment packing is 800 pounds of packing weight multiplied by the tons of forage delivered per hour. For every foot of rise there should be 3 feet of “run,” or horizontal distance, or a one-to-three slope. This creates a long gently sloping ramp angle of about 18 degrees.

The sides should also be packed at an 18-degree slope. Remember, overpacking at the end of the day or before covering won’t improve overall bunker density and can create a layer of spoilage from broken plant tissue.

If one of these harvest decisions breaks down, the expectations for the inoculant performance will change. Inoculants can help prevent a bad situation from getting worse by delaying or limiting the amount of spoilage or decomposition. However, as with any management decision, stacking the deck in favor of your inoculant is the best strategy of all. PD

The foregoing is provided for informational purposes only. Please consult with your nutritionist or veterinarian for suggestions specific to your operation. Product performance is variable and subject to a variety of environmental, disease and pest pressures. Individual results may vary.

Evaluate the effectiveness of your inoculant at feedout with a trusted adviser.Photo courtesy of Bill Powel-Smith.

bill powel-smith

Bill Powel-Smith
Dairy Specialist
DuPont Pioneer