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Including glycerol, a byproduct of biodiesel production, in feedlot diets

February 15, 2010

[Source: Jolene Kelzer, University of Minnesota Beef Team, for Farm & Ranch Guide]

Alternative fuel production in the United States has played an integral role in providing non-traditional feedstuffs for ingredients in livestock diets.

Major co-products resulting from corn-milling processes that ferment corn grain into ethanol include dried, wet, and modified distillers grains plus solubles, corn gluten feed, and condensed distillers solubles.

Research supports inclusion of these co-products in feedlot diets at various levels to provide cost-effective replacements for traditional energy and protein feed ingredients.

In addition to ethanol production, biodiesel production has, and will continue to, increased exponentially as the U.S. strives to reduce its dependence on foreign oil. Biodiesel is suggested to burn cleaner and more efficiently compared to petroleum-based diesel, and is thus blended into the national fuel supply to reduce emissions of unburned hydrocarbons, carbon monoxide, and carbon dioxide.

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–>The major byproduct of biodiesel production is crude glycerin, also known as glycerol. Glycerin is a sweet-tasting, colorless, viscous liquid produced at a rate of 7.6 pounds (approximately one gallon) per 10 gallons of biodiesel.

Within the next decade, the supply of crude glycerin from biodiesel production is estimated to reach 1.4 billion pounds.

Crude glycerin can be purified for use in human products such as cosmetics, pharmaceuticals, and a variety of food items. Purification of crude glycerin is a costly and energy-intensive procedure; therefore, glycerin intended for livestock consumption is normally not purified.

The price of crude glycerin is principally driven by demand, and therefore can be quite variable and range from $0.05 to $0.37 per pound, depending on location of the biodiesel plant.

Common feedstocks used in biodiesel production include vegetable oils, mainly derived from soybeans, cottonseed, or canola, animal fats such as tallow, or a combination of both vegetable oil and animal fat. Largely due to the different feedstocks used for biodiesel production, the composition of crude glycerin on a dry matter (DM) basis will vary and may consist of 80-90 percent glycerol and as much as 8 percent fat or more.

Additionally, glycerin contains little or no protein but has net energy values similar to or greater than corn grain. These energy values largely depend on the concentration of fat in the glycerol and also the type of diet in which it is included (net energy for gain is reported to be 0.61 Mcal/lb in high starch diets vs. 0.70 Mcal/lb in low starch diets).

Prior to feeding glycerin, contaminant levels and impurities should be known to ensure the product is safe to feed to livestock. The methanol concentration of crude glycerol is of particular concern and should be less than 150 parts per million if intended for livestock consumption.

Additionally, glycerol should be introduced gradually into the diet, especially when included at high levels, to allow adequate time for the rumen environment to adapt to the diet change without reducing feed intake.

To date, glycerol has been effectively added as an ingredient in liquid supplements. The sweet liquid can also be used as a conditioning agent to improve palatability of dry diets.

Glycerol can effectively control dust and reduce buildup of fines in bunks by preventing separation of ingredients, particularly in total mixed rations containing concentrates with small particle sizes. As the biodiesel industry expands and availability of glycerin increases, there is great potential to include glycerin in livestock diets as a replacement for corn grain.

While published research is limited evaluating glycerol as a feed ingredient in livestock diets, some studies suggest promising results.

Glycerin is rapidly fermented in the rumen of cattle, which may also explain its relatively high energy value as a feedstuff. When fermented, glycerol is reported to shift volatile fatty acid production in favor of increased propionic acid, the only major gluconeogenic volatile fatty acid. Propionate is absorbed through the rumen wall and subsequently, circulatory glucose concentrations increase to improve energy efficiency in cattle.

Several universities have conducted research evaluating glycerol as an ingredient in feedlot diets. Some of the first reported work from Illinois has suggested a 10 percent reduction in dry matter intake, an 11 percent increase in average daily gain, and therefore a 22 percent improvement in feed efficiency of steers when glycerol replaced 10 percent of the dry-rolled corn in finishing diets.

However, when glycerol replaced 10 percent of the dry-rolled corn in finishing diets containing 30 percent distillers grains, the effects of glycerol on steer performance were still positive but not as significant.

In this experiment, average daily gain increased only 2.5 percent with a 16 percent improvement in feed efficiency when 10 percent glycerol was included in diets containing 30 percent distillers grains. Results of these experiments suggest glycerol is an excellent alternative energy feedstuff in finishing diets and can improve feedlot performance when included at levels up to 10 percent dietary DM.

Researchers at Kansas State University evaluated levels of 2, 4, 8, 12, and 16 percent glycerin in steam-flaked corn diets on feedlot heifer performance and carcass characteristics. At levels of 2, 4, and 8 percent glycerin, average daily gains improved 13, 8, and 5 percent, respectively.

However, at levels of 12 and 16 percent glycerin, average daily gains were reduced by 2 and 13 percent, respectively.

Dry matter intake was not affected at low levels (0 and 2 percent inclusion), but was linearly reduced as level of glycerin increased from 4 up to 16 percent of the total diet.

The greatest feed efficiency improvements were reported with lower levels of glycerin inclusion, with observed 11, 10, and 7 percent improvements when 2, 4, and 8 percent glycerin was fed.

Glycerin inclusion also had an effect on carcass characteristics in this experiment. Hot carcass weights were increased 18, 11, and 7 pounds in heifers fed 2, 4, and 8 percent glycerol, respectively.

Marbling scores and backfat depth were linearly reduced as inclusion level of glycerin increased, therefore reducing the percentage of heifers grading USDA Choice and subsequently increasing the percentage of heifers grading USDA Select.

When cattle are marketed on a quality grid, this negative effect on marbling may impact profit margins for both producers and processors even though carcasses were leaner.

These data suggest glycerol included up to 8 percent of the total DM in steam-flaked corn-based finishing diets may be favorable for cattle performance, but the greatest benefits observed in feedlot heifer gain and feed efficiency occurred when glycerol was included at 2 percent of the diet DM.

Most research suggests feeding glycerol in finishing diets at low levels (five percent of the total diet or less) in place of corn grain can improve animal performance. In vitro studies have demonstrated levels of glycerol greater than 5 percent may alter the rumen environment and subsequently reduce intake by limiting growth and activity of certain fiber-digesting bacterial and fungal populations.

However, continued research is necessary to gain a more complete understanding of how metabolism of glycerol affects the rumen environment.

This information will help clarify effects of glycerol on nutrient digestibilities and subsequent animal performance variables to further establish recommended levels of inclusion in different types of feedlot diets.

Because of glycerol’s chemical properties, there could be potential limitations for handling and storage of this feedstuff. Feed-grade glycerol is a highly viscous liquid that does not flow well in cold temperatures and has a tendency to absorb and retain moisture. These properties may create flowability issues when glycerol is included in dry diets provided to livestock in self-feeders.

To overcome cold weather impacts, educators suggest adding water to improve flow properties for easier handling. However, adding water will change the DM content of the glycerol, so ration adjustments are necessary to achieve desired levels of glycerol inclusion on a DM-basis.

If glycerol is readily available at economically feasible prices, monitored for methanol and other impurities according to FDA regulations, handled and stored properly, and fed at recommended levels, this sweet byproduct of the biodiesel industry could become a popular feed ingredient in livestock diets in the near future.

For more information regarding beef feedlot nutrition, visit the U of M Beef Team website at: http://www.extension.umn.edu/beef.

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