Feed and Fuel

Texas researchers successfully demonstrate the use of glycerin in cattle diets
By Erin Voegele | May 01, 2012

The biofuels and livestock industries have a history of discord when it comes to the use of corn and soybeans as feedstock for biofuel production. Feed research conducted at Texas AgriLife Research and West Texas A&M University, however, is showing that crude glycerin resulting from the biodiesel production process can be used to reduce feed costs by offsetting a portion of corn in forage diets. 

For the past two years, Jim MacDonald, an AgriLife Research beef cattle nutritionist, and Mike Brown, a professor of ruminant nutrition and management at WTAMU, have teamed up to conduct four experiments designed to determine the value of feeding crude glycerin in beef growing and finishing diets. The studies were funded by a grant offered by the Texas Department of Agriculture and the U.S. Department of Transportation South Central Sun Grant program. According to MacDonald, the research has shown that crude glycerin meeting certain quality standards can safely be added to cattle forage diets at rates of up to 7.5 percent.

It is important to note, however, that not all crude glycerin produced by the biodiesel industry is of the same quality. The crude glycerin used in the feed trials met certain quality standards related to methanol, salt and fat content.

“All of our glycerin was less than 0.5 percent methanol,” MacDonald says. “That’s important because the amount of glycerin we are able to include in the diet can be limited by methanol.” Regarding sodium content, glycerin utilized in the trial contained 3 to 3.5 percent sodium. “From the perspective of the livestock producer, sodium can limit intake,” MacDonald adds. “If you get too much sodium, or you go too high with your crude glycerin inclusion rate, you can limit intake.” Finally, the glycerin had a fat content of less than 1 percent. Ruminants can only handle up to 6 or 7 percent total dietary fat. “Large swings in dietary fat composition or dietary fat content can also cause problems,” MacDonald says. For that reason, crude glycerin that has variability in fat content will not be attractive to livestock producers.

In fact, MacDonald names glycerin consistency as one of the most important factors a biodiesel plant should achieve in order to produce a byproduct marketable to the feed industry. While industry-wide consistency in glycerin quality would be ideal, he says that an individual plant should be able to develop its own market for crude glycerin by ensuring that the byproduct it produces can consistently meet quality specifications required by a feed supplier. He also notes that, from a feed perspective, using potassium hydroxide as a catalyst instead of sodium hydroxide would be preferable. The presence of potassium in the glycerin would actually be beneficial, he says.

While MacDonald’s research has obviously had positive implications on the technical level, he also notes that the trials success demonstrates positive findings on a much higher level. “It demonstrates that there are opportunities for symbiosis between bioenergy and livestock production,” he says. “The ability of livestock producers to use [biofuel] byproducts reduces the amount of feed that they need from corn or soybean meal.”

—Erin Voegele

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