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Corn+Soybean Digest

Wet Distillers' Grains Play a Postive Role in Food Vs. Fuel Debate

The old argument that we're wasting feed to produce fuel is an empty argument. Contrary to what some have concluded, when ethanol's byproduct — wet distillers' grains — is added to corn stalks and fed to cattle, we actually get about the same feed value as, or in some cases more than, from corn grain alone. Here's why.

The food-fuel debate has focused on two arguments: energy efficiency and the potential of using a food source for fuel.

The energy-in, energy-out debate has been settled with analysis clearly indicating that corn ethanol is fuel-efficient. A typical South Dakota no-till farmer, for example, uses 3 gal. of diesel to grow 150-bu. corn, which produces 420 gal. of ethanol. Nitrogen, P and K are a significant energy input in the production of corn but there is no N, P or K in CH3CH2OH (ethanol). The N, P and K are conserved and found in distillers' grains.

Energy efficiency at ethanol plants continues to improve. In fact, energy into the plant is a fraction of the energy out of the final ethanol product.

Recently there's been an additional argument that ethanol has and will cause land-use change in other countries, and this will lead to an increase in carbon emissions (see footnote on p. 50). The argument is that these carbon emissions should be charged to corn ethanol. Is this argument valid?

Prior to ethanol production, corn stalks and small-grain straw were not considered to have much feed value because of low protein content and the absence of a low-cost, high-protein product to mix with them.

R.L. Preston in his feed composition tables in BEEF magazine and on BEEF 's Web site ( lists the crude protein content (dry matter basis) of corn stalks at 5%, wheat straw at 3% and oat straw at 4%. As ethanol is processed, a bushel of corn (56 lbs.) produces 2.7-2.8 gal. of ethanol and about 18 lbs. (dry) or about 45 lbs. (wet) of the coproduct, distillers' grains.

Preston's table indicates that distillers' grains from corn ethanol plants typically has a crude protein content (dry matter basis) of about 30% wet and 28% dry.

I remember the 7-9-11 rule of thumb of protein content for feeding beef cows, indicating the target percent crude protein on a dry-matter basis that is typically in the optimum ration at different stages of beef cow pregnancy and after calving.

There's also the 14-12-10%protein rule for feeding calves at different stages of maturity. If distillers' grains are too high in protein and stalks, and straw is too low in protein to be good feed by itself, then mix them together for a viable ration.

AN INDIRECT IMPACT of the production of ethanol is that we now have a low-cost, high-protein feed (distillers' grains) that is being mixed with low-protein (previously unharvested), low-cost stalks and straw to make a viable feed.

Referencing the table above, looking at 1 bu. of corn, we see in Preston's data that it contains 43.4 lbs. of total digestible nutrients (TDN) and 4.4 lbs. of crude protein (CP).

For each pound of grain produced, a modern corn plant produces a pound of stalk (plus leaves). To maintain soil productivity you must return about 40% of the stalks to the field. This indicates that it is acceptable to remove 60%, or 33.6 lbs., of stalks for every bushel harvested.

Even in areas where over 33-55% of corn goes to ethanol, the stalks from acres not producing ethanol are available as feed. This means an additional 33.6 lbs. of stalks/bu. of corn are available for feed.

THE BEEF CATTLE ration is about 11% protein (dry weight basis).To create this from wet distillers' grains (WDGs) and stalks, using all of the WDGs from a bushel of corn (45 lbs.) we need to mix 57 lbs. of stalks. With this ration (45 lbs. WDGs and 57 lbs. of stalks) we have 41.9 lbs. TDN and 6.8 lbs. CP. This compares with the original bushel of corn that contained 43.4 lbs. of TDN and 4.4 lbs. of CP.

For every 1 bu. of corn, you get 45 lbs. of WDG. And to get 11% protein, you need 57 lbs. of stalks (1 lb. of corn yields 1 lb. of stalks).

After considering this additional indirect effect of ethanol production, and using stover and straw as a feed, the TDN and CP from a corn field are essentially the same for corn going to an ethanol plant and for corn used as feed.

So there's no loss of feed value or issues with indirect land use when adding ethanol's byproduct, WDGs, to corn stalks to feed cattle.

Background footnote

In 2007 the Energy Independence and Security Act (EISA) set the lifecycle greenhouse gas emission thresholds for renewable fuel and compares greenhouse gas emission of fuels such as ethanol with the average of petroleum fuels greenhouse gas emission in 2005.

ESIA defined “lifecycle greenhouse gas emission” to included direct and indirect emissions. Searchinger and others wrote a paper in Science, Feb. 29, 2008,(vol. 319, no. 5867, p. 1,238-1,240) arguing that since the law required that indirect effects must be included in the analysis, that “analysis has failed to count carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new crop production to replace the grain (or cropland) diverted to biofuels.” This argument is based on lost feed value as a result of processing corn into ethanol.

To better define the impact of the loss of feed, EPA models how much indirect land use change would occur. To the casual observer this makes perfectly good sense, but to a Midwest agronomist there is a significant problem because all indirect management practices are not being considered.

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