I keep a list of past articles I’ve written for FARMING magazine, dating back to the first one in December 1997. (This column, including the one or two feature articles I write each year, is #217.) It’s been over two years since my last article on silage inoculants; since this is commonly a hot topic with farmers and agribusiness professionals it’s time for a review and an update of inoculants and of recommended ensiling practices in general.

Photo couresty: vschlichting/istock

An “optional extra”

First, a statement that initially may unsettle those selling silage inoculants: Farmers can make good silage without using a silage inoculant. This is obvious since farmers were making good silage long before the availability of commercial silage inoculants. The naturally-occurring fermentation bacteria on forage plants will sometimes result in good silage as long as the other essentials of silage-making are followed – correct dry matter content, chop length, packing and covering. One summary of a large number of silage inoculant trials found that inoculants “worked” – by limiting dry matter losses, increasing milk production or both – in about 75 percent of the trials. That leaves one trial in four where the inoculant didn’t do anything positive that the researchers could measure. Another research summary found that compared to no inoculant, milk production increased in 50 percent of the trials where a silage inoculant was used.

Since it’s possible to make good silage without using an inoculant, why use one? While the cost varies depending on crop, yield, and inputs, by the time you ensile a forage crop you probably have at least $50 invested in each ton of silage. If a silage inoculant cost $10 per treated ton farmers might think twice before using one. But at a fraction of that cost – often $1 or less for a basic product – it should be an easy decision and indeed, recent surveys show that most dairy farmers use silage inoculants. Each dollar invested in silage inoculants will return several dollars in increased silage quality and/or quantity. Therefore, using a silage inoculant is simply a cost-effective form of crop insurance.

Fermenting forage crops: What’s important

Dry matter – Silage inoculants work best when the ensiled forage is at least 30 percent dry matter. Low dry matter forages can take longer to ferment, and in the process may produce large amounts of acetic and butyric acids. The longer it takes forage to ferment the more dry matter is lost, and (especially in legume silages) there can be an excessive breakdown of protein. The primary product of forage fermentation is lactic acid, and most inoculants are designed to increase the production of this acid. Some silage inoculants contain Lactobacillus buchneri, resulting in the production of acetic acid that delays the heating of silage when it’s exposed to air during feedout. Commercial inoculants containing L. buchneri have become popular and are sold by several companies. As noted, low dry matter silage can also produce butyric acid, and this is never good. Forages that sit in the field for a long time after mowing can also produce butyric acid, even when dry matter content is 35 percent or higher. As butyric acid content approaches 0.5 percent there’s a good chance that Clostridial fermentation has occurred, resulting in a significant loss of quality and often refusal by livestock. Livestock refusal is because butyric acid silage stinks and cows don’t like the odor (similar to rotting meat) any more than we do. Generally forages should be ensiled at dry matter contents ranging from 30 percent to 45 percent. Attempting to ensile forage that’s too dry can cause packing difficulties, often resulting in high levels of yeasts and molds. While some farmers are successful at ensiling forages higher than 45 percent DM – particularly with wrapped bale silage – this can be a risky business.

Silage pH – The goal is for the pH level of just-ensiled forage to decline quickly. The faster the pH decrease the less dry matter lost during the fermentation process. Whole plant corn is one of the easiest forages to ensile since it’s loaded with sugars and is low in crude protein. Legume silages usually have a slower rate of pH decline, and terminal pH is almost always higher than with corn silage. Grasses are in the middle unless they’re very high in protein due to excessive nitrogen application and/or very early harvest. An abnormally high pH is almost always an indication that something went wrong. When it comes to silage, “the nose knows.” That characteristic silage odor is due to acetic acid, not lactic acid which is almost odorless. An odor like something died in your silage – that’s butyric acid. A sweet, tobacco-like odor is a sign of heating and unavailable (bound) protein due to overly high DM.

Packing silage – Silage density is influenced by several factors. Height of the silage is one, which is why you can get away with drier forage in the bottom half of an upright (tower) silo better than you can in the top half. With other forms of silage storage the farmer has to provide an assist – hydraulic pressure in the case of bagged and plastic-wrapped silage, packing with tractors or other heavy equipment on bunker silos and drive-over piles. Silage density is also influenced by particle length and forage dry matter. Wetter silages are often ensiled at longer chop lengths to reduce effluent losses, a serious consideration when harvesting forage that’s under 30 percent DM. Forage species also makes a difference: When I was managing the Miner Institute crop operation (in Chazy, New York) we occasionally ensiled mixed, mostly alfalfa silage in bunker silos at over 40 percent DM with no problems. However, trying to ensile grass forage at over 40 percent DM, especially stemmy first-cut grass, would result in low silage density and mold problems. We ran into problems ensiling high-DM grass in silage bags, learning the hard way that there’s a big difference between bagging first-cut grass at 32 to 35 percent vs. at 40 to 45 percent DM.

The keys to successful silage making include harvesting at the correct dry matter content and chop length, ensiling immediately, packing well, then covering with a high quality silage plastic that’s properly weighted down. These steps will give you a good chance of making good silage. But you’ll make better silage more often by using a silage inoculant.