Farming Magazine - February, 2013


Forages: The Latest on Silage Additives

By Everett D. Thomas

I keep a dated list of all the articles I've written for Farming over the years, in part to avoid revisiting a topic that I've covered in the past year or so unless there have been meaningful changes. In the case of silage additives, my last column on this topic was well over two years ago, so it's time to take a fresh look at silage additives.

Additives versus inoculants

Note that the title includes the word "additives," not "inoculants." That's because not all silage additives are bacterial inoculants. There are commercial additives that are primarily nutritive sources, intended to provide food for the native fermentation bacteria on forages after they're ensiled.

Most silage inoculant trials involving a wide variety of products show improvements in silage quality and/or dry matter retention when compared to forage that wasn't treated with a commercial silage inoculant. Most trials, but by no means all: Sometimes the native bacteria on the forage are sufficient to make good silage. This stands to reason, since farmers were making good silage for generations before commercial inoculants appeared on the market.

Some silage additives contain bacterial inoculants and include enzymes intended to break down plant cell walls. Although it's not commonly done these days, anhydrous ammonia has been used (primarily on corn silage) to increase the crude protein content of the silage and to preserve the forage. Finally, acid additives result in direct acidification of the forage, essentially short-circuiting fermentation bacteria whose job it is to produce silage acids, including lactic and acetic acid. Formic acid, while not used in the U.S. for this purpose, is a popular silage additive in Japan and is quite effective when used properly.

Many products, many claims

It's easy to understand how farmers can get confused about silage additives. There are at least half a dozen national and international companies selling bacterial silage inoculants, and each company has the "best product on the market." If you're in doubt about this, ask the company's representative.

One product contains a combination of fermentation bacteria and enzymes and will not only preserve the forage, but will increase its fiber digestibility. Another includes a particular bacteria, Lactobacillus buchneri, which produces acetic acid - the main ingredient in vinegar - and greatly reduces aerobic spoilage and heating on the silage face and in the feed bunk. A third claims to be just as effective as the more expensive products at less than half the cost.

It's not the purpose of this column to promote one brand over another, and most of the bacterial inoculants (representing the majority of silage additives), when used properly, will indeed improve silage quality and/or reduce fermentation losses. Read that sentence again, focusing on the words "when used properly." This means not only applied at the correct rate, but also applied in such a way as to impact the entire mass of forage being ensiled.

Most silage inoculants contain Lactobacillus plantarum plus several other acid-producing bacteria. It's worth noting that while there are a lot of silage inoculants on the market, only a few companies actually produce (grow) the bacteria used in these inoculants.

The standard application rate for most inoculants will result in 100,000 colony-forming units (CFU) per gram of fresh forage. University research has shown that the effectiveness is reduced if a significantly lower-than-recommended rate of inoculant is used. Use much more than the recommended rate, and economics suffer - less bang for the buck. Inoculants containing L. buchneri are typically recommended at a higher rate, up to 400,000 CFU per gram of forage. There's research to back up these higher rates.

Application method is important, because silage inoculants don't move around much within the silo. The objective is to attain the completest coverage possible. This is usually done by spraying or dripping the inoculant onto the forage as it's chopped, and even if every silage particle doesn't come in contact with the inoculant solution, the combination of unloading and silo filling will usually do the rest of the job.

In the western U.S., where much of the forage crop is harvested by custom operators, a method called the "Texas shower" is popular. In this method, a truck of chopped forage is driven under an overhead boom and the inoculant solution is sprayed on top of the forage. However, recent research found that this method doesn't work as well as applying the inoculant at the chopper.

Liquid versus granular inoculants

I prefer water-dispersible inoculants, typically sold in tinfoil packets or plastic containers, to bags of granular inoculant for three reasons, one practical and the other two technical.

On a practical basis, handling a packet of inoculant weighing a few ounces is a lot easier than toting around bags of granules. Leftover packets can be refrigerated to extend their shelf life, though there's a limit to this, so it's best to use up inoculants during the year they're purchased.

Now for the technical reasons. First, it's easier to achieve good inoculant distribution when the product is applied in solution. While it's possible that good distribution can be achieved by using a granular applicator - most often done with silage bagging operations - I've seen too much granular inoculant applied by the "coffee can method." This entails dumping a truckload of chopped forage and flinging a can or two of inoculant over the pile, hoping for the best. Second, there must be sufficient moisture in the chopped forage for the bacteria in the granules to become activated. At a typical silage moisture of 35 percent (plus or minus a few percentage points) this isn't usually a problem, but sometimes hay crop silages get a bit too dry and are ensiled at over 40 percent dry matter. Research has shown that while the bacteria in the granular product eventually become active, if forage dry matter is too high, there's a time lag in the process, and with silage fermentation, speed is important in minimizing dry matter losses.

Silage inoculant economics

No detailed calculations are needed here; many studies have found that most silage inoculants "work" (improve quality and/or dry matter retention) most of the time, and with the modest price of most commercial inoculants, the return on investment is many times the cost. High milk prices and high-priced forage further improve the economics.

Milk prices are not all that high - most farmers would say not nearly high enough - but across much of the country, forages are at record high prices, so every pound of dry matter preserved through the use of a silage inoculant is worth more to the farmer.