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Glycerol: a syrupy, sweet liquid used to make products we utilize on a daily basis, such as cosmetics, pharmaceuticals, antifreeze, baked goods, detergents and more.
Whether we realize it or not, glycerol appears in our grocery carts every time we shop.
What many people, particularly livestock producers, don't know is that glycerol also has an energy level within a few percentage points of corn. Researchers in the Midwest have been experimenting with ways to incorporate glycerol into cattle diets - and several have had success.
Based on research from South Dakota State University, feeding glycerol as part of a corn silage grower diet in over-winter calves resulted in exceptional gain, according to Robbi Pritchard, ruminant nutritionist at SDSU who led the research.
"The more you put in a corn silage diet, the more they eat and the faster they grow," Pritchard said. "We experienced phenomenal performance. Cattle were performing like they were on a high-concentrate diet."
Researchers Parsons, Shelor and Drouillard from Kansas State University had similar results in 2008 when they experimented with glycerol as part of a steam-flaked corn and alfalfa finishing diet. They wrote in Journal of Animal Science that, "Adding glycerin to cattle finishing diets improved weight gain and feed efficiency, particularly when added at levels of 8 percent or less of DM (dry matter) basis."
If glycerol increases performance, why aren't feedlots across the United States supplementing corn rations with glycerol? The answer lies partly in supply and demand principles and partly in toxic impurities found in glycerol.
Glycerol, or glycerin, is a byproduct of biodiesel production. Though the fat required to produce biodiesel can come from either soybean oil or animal sources, most glycerol results from soybean-based biodiesel production. About 1 gallon of glycerol is produced for every 10 gallons of biodiesel manufactured, according to Harold Tilstra, national co-products technical support for Land O' Lakes Purina Feed.
When biodiesel became a viable energy source in the early 2000s, animal nutritionists anticipated a large supply of crude glycerol to hit the market, and many did research on how to use it in livestock diets, said Al Miron, former beef and sheep nutritionist for Land O' Lakes Feed in Ellis, S.D.
But when biodiesel production dropped in recent years, the supply of glycerol went down and the price went up.
"I think everybody probably expected biodiesel production to really take off and be a more important energy source, but it hasn't," Miron said. "At this point, it probably hasn't materialized to the extent that we thought it would a few years ago."
Because the glycerol supply is limited, there isn't much left for use in livestock feed. According to the National Grain and Feed Association, 450 million to 500 million pounds of glycerol is produced annually in the United States, with most of that supply being channeled to products intended for human use.
"Bottom line, yes, it is a viable animal feedstuff," said Ron Marr, biodiesel marketer at Minnesota Soybean Processors in Brewster, Minn. "At the same time, it depends on the cost of that feedstuff going in. It's been documented that it works, so now it's becoming a potential feedstuff depending on the economics."
There are two forms of glycerol on the market: crude and purified. Crude glycerol, which is used in livestock feed, is 85 percent glycerin and 15 percent other impurities. Purified glycerol, which is much more expensive, is reserved for human products.
The most worrisome impurity found in glycerol is methanol, a substance used in the biodiesel-making process. Other salts and heavy metals exist in crude glycerol as well.
"The crude glycerol from biodiesel production oftentimes contains some methanol as an impurity," Miron said. "Methanol is really quite toxic and FDA does not recognize glycerol with more than 150 parts per million to be generally recognized as safe."
Generally recognized as safe (GRAS) means the Food and Drug Administration recognizes a given substance as safe for its intended use. Crude glycerol is GRAS for use in livestock feed, but only if methanol levels are at or below 150 parts per million (ppm). Anything over that, says the FDA, is unsafe and illegal.
According to Tilstra, producers are responsible for ensuring that any crude glycerol they buy meets FDA requirements.
"I would want laboratory verification that the product I was feeding was safe," Tilstra said. "I wouldn't assume it was safe without knowing that."
Pritchard said producers need to either buy glycerol from a source that intends it for livestock consumption or get it tested prior to use.
"There are people selling glycerol that is not feed grade glycerol," he said. "The most common issue is being contaminated with methanol and it can have some other heavy metal contaminants in it. [Producers] need that's in that product."
But producers don't need to be concerned about methanol levels in glycerol unless they buy it in bulk. Glycerol is present in liquid feed supplements already on the market, such as some of those sold at Midwest Ag Enterprises in Marshall, Minn. Glycerol levels in products like these are so low that methanol isn't a concern.
Randy Lessman, feed products manager at Midwest Ag Enterprises, said the company sells glycerol in pre-mixed liquid supplements, not alone in bulk.
"We're using it as just another ingredient in our supplements," Lessman said. "Most of our cattle feeders who are using it, they're either feeding the supplement about half to three-quarters of a pound a day as part of their protein supplement."
Producers shouldn't rule out glycerol being used as a feedstuff in the future, however. Gains in the biodiesel market are certain to result in more and cheaper glycerol on the market. And with the Obama administration's goal to cut greenhouse gas emissions by 20 percent by 2020, industries like biodiesel and ethanol will likely expand.
"Presumably, biofuels in the long-term are going to continue to grow. When we were doing the experiment, it was not a cost effective time to do the glycerol," Pritchard said. "But we thought it was important to get it done and have the data available so that the next time there is a lot of it on the market at a really low price, people have the info they need to capitalize on it."
The SDSU study incorporated glycerol into corn silage grower diets in backgrounding steers at rates of zero, 8, 16 and 24 percent of the dry matter intake.
The average daily gain for steers consuming 24 percent glycerol was 3.97 pounds per day with 19.45 pounds of dry matter intake (DMI) per day.
Steers at 8 percent and 16 percent glycerol gained about 3.5 pounds per day with 19.15 and 19.2 pounds of DMI per day, respectively. Steers consuming no glycerol gained 2.96 pounds per day with 17.78 pounds of DMI per day.
Pritchard said the results were comparable to steers fed a corn-based, 90 percent concentrate finishing diet.
Pritchard and his team then rolled the steers into a finishing diet study and dropped glycerol levels to zero, 5, 10 and 15 percent. He found that glycerol isn't as beneficial in a finishing situation. With a high-concentrate diet, Pritchard said that even 5 percent glycerol negatively impacted performance.
Alfredo DiCostanzo, professor of beef cattle nutrition and management at the University of Minnesota, is conducting research about glycerol in finishing diets. He is comparing four diets: distillers grain with 10 percent glycerol, distillers grain alone, a control diet with 10 percent glycerol, and a control diet.
He said that while it's too early to know for certain, it appears that the glycerol-fed animals in the finishing stage, like those at SDSU, are consuming less.
"We do notice that there is a little bit of an intake response," DiCostanzo said. "As far as the glycerol-fed animals, they are eating slightly less. Of course, these are more observational than anything else right now."
DiCostanzo said reduced intake doesn't always mean reduced gain. As the Kansas State University study found, glycerol can lower feed intake but improve efficiency through better gains.
"The reduction can go both ways," he said. "If they reduce intake and still have the same gain, then you are going to have better efficiency."
Glycerol has other benefits besides improving gain and efficiency in cattle. It is easy to store during the winter because adding small amounts of water periodically will keep it from freezing. Since glycerol is a slippery substance, it does not cake to mixers or feed bunks. It also sweetens feed and makes it less dusty.
If fed in the correct amount and monitored for methanol levels, Miron said glycerol is a safe, viable feed supplement.
"As long as FDA guidelines are followed, then it's very safe," he said.
Johnson, S. 2009. Incorporating glycerol into cattle diets. Farm & Ranch Guide, Bismarck, ND. 12/10/09. http://www.farmandranchguide.com/feature/livestock_guide/incorporating-glycerol-into-cattle-diets/article_cc072557-7c31-502d-92f7-0a6288197f3c.html