Biofuel research isn't just a matter of finding the right type of biomass - corn grain, soybean oil, or other material - and converting it into fuel. Scientists must also find environmentally and economically sound uses for the co-products from biofuel production.
By Alfredo Flores and Ann Perry, Agricultural Research Service Information
When producing 100 litres of biodiesel from soybean oil this also yields around eight kg of crude glycerine. When this glycerine is refined to 99% purity, it can be used in many products, including pharmaceuticals, foods, drinks, cosmetics, and toiletries.
Livestock and poultry producers are looking for new sources of feed supplements to save costs and boost nutrition. “Several scientists have shown that it is possible to supplement pig diets with dried distiller’s grains, which remain after ethanol production. Though this can result in equivalent animal productivity, it can also result in increased manure production—and higher levels of volatile organic compounds, which may increase odour emissions,” says animal nutritionist Brian Kerr, who works at the ARS Swine Odour and Manure Management Research Unit at Ames, Iowa. “We decided to look at using the co-products from biodiesel production as feed supplements because no such data was available to the livestock industry.”
Kerr partnered with animal scientist William Dozier - formerly in the ARS Poultry Research Unit at Mississippi State and now with Auburn University - and Iowa State University colleague Kristjan Bregendahl to see whether crude glycerine could be used to supplement livestock feed.
Pigs do well on glycerine
Kerr led studies that examined how crude glycerine feed supplements affected pig energy use. In five different experiments, he supplemented the diets of starter pigs and finisher pigs with different levels of crude glycerine. Overall, these studies showed that the sample of crude glycerine contained an apparent metabolisable energy (AME) concentration of 3,207 calories per kilogram (kcal/kg). AME is a standard measure of energy used in nutritional studies.
Pigs fed the crude glycerine were able to digest it efficiently, and it provided them with a supply of caloric energy that basically equalled that of corn grain. A follow-up study showed no effects on weight, carcass composition, and meat quality in pigs fed diets containing 5% or 10% crude glycerine from weaning to market weight.
Layers and broilers supplemented
Meanwhile, Dozier and Bregendahl evaluated the use of glycerine supplements in poultry feed. They used 48 egg-laying hens and 1,392 broilers in four research studies. After feeding four levels of crude glycerine to laying hens, Bregendahl determined the AME in the crude glycerine to be 3,805 kcal/kg. He also compared feed consumption, egg production, egg weight, and egg mass (calculated by multiplying egg production and egg weight) and found no significant differences among the four groups. “Glycerine supplements were well utilised for egg production by the hens,” he says.
Dozier, meanwhile, conducted three broiler studies. In his first study, young broilers consumed either a control diet with no glycerine supplementation or feed with a 6% glycerine content. His results indicated that glycerine provided the 7 to 11- day-old broilers with an AME of 3,621 kcal/kg. Later research resulted in similar findings for older broilers. Glycerine supplements at varying levels provided 21 to 24-day-old broilers with an AME of 3,331 kcal/kg and 42 to 45-day-old broilers with an AME of 3,349 kcal/kg. Overall, the data indicates that crude glycerine is an excellent source of energy in pig and poultry rations and can be used without harming animal performance, carcass composition, or meat quality.
More research needed
“This research project has been a success so far,” says Dozier. “We will have a total of six peer-reviewed papers from this research, and we’ve been invited to present the results at national and international nutrition conferences. But we still need additional research on how to handle glycerine as an alternative feedstuff for swine and poultry in integrated feed mills.” He also notes that from a nutritional standpoint, this technology can serve as an alternative dietary energy source that could result in lower feed costs.
Crude glycerine does contain small amounts of methanol and salt, which could potentially limit its use as a feed supplement. Additional studies might be needed to assess how much methanol livestock can safely ingest in glycerine supplements, which would help regulators refine US standards for using crude glycerine in livestock feed. But as US biodiesel production continues to boom, crude glycerine supplements could be a win-win situation for biodiesel producers and farmers alike. “Swine and poultry producers are very interested in supplementing livestock feed with glycerine,” Kerr notes. “This way, crops can be used for both biofuels and for livestock at the same time.”
This article was previously published in the April 2009 issue of Agricultural Research magazine.