The rapid growth of ethanol and biodiesel production in the United States and elsewhere has raised questions about possible uses for the byproducts of this industry. To date the use of ethanol byproducts, in particular distillers' dried grains with solubles, in animal feed has received much attention. The burgeoning biodiesel industry on the other hand, has resulted in glycerine, the principal byproduct, flooding the market. While glycerine is widely used in the soap, cosmetic and food industries, the biodiesel industry is producing more than the market can cope with. This has led to renewed efforts to find new uses for glycerine, e.g. as a boiler fuel source, as animal feed, for the production of propylene and ethylene glycol, and the possibility of glycerine replacing petrochemicals.
Although several studies have evaluated the use of glycerine in diets for poultry, pigs and ruminants [1-8], its high cost then meant it was not cost-effective to use as an animal feed. However, the current low cost of glycerine and its value as an energy source has prompted several research groups to evaluate the nutritive value of glycerine and its use in livestock diets.
Researchers at the University of Arkansas' Center of Excellence for Poultry Science examined the possibility of using glycerine as a dietary supplement in growing broiler chickens. In a short-term preliminary trial, Park Waldroup and his research team found that as much as 10% glycerine could be fed to to chickens up to 16 days of age without any detrimental effects on growth performance or meat quality. While 5% glycerine had no effect on body weight, feed intake, feed conversion or mortality, 10% glycerine affected feed flow rate (in the feeders used), reducing feed intake and consequently reduced body weight. Although the results suggest that glycerine can be used as an energy source in broiler diets, Waldroup cautioned that additional research was needed to evaluate the quality of the glycerine used and its effect on feed texture and pellet quality.
Researchers from Iowa State University and the US Department of Agriculture have been conducting studies on the feasibility of using glycerine in pig and poultry diets. In a metabolism study in which nursery and finishing pigs were fed 5, 10 and 20% glycerine, glycerine was readily used by pigs and found to have an energy value similar to corn. In a growth study, pigs fed on 5 and 10% glycerine from weaning to market weight showed the same growth performance as those fed on a conventional corn-soyameal diet. When 20% glycerine was used, flow rate problems were encountered leading the researchers to conclude that 10% inclusion was perhaps the upper limit. A metabolism trial conducted with hens fed on 0, 5, 10 or 15% glycerine showed no adverse effects on egg production, egg weight, or feed intake; the energy in the glycerine was also efficiently utilised. Although data from these trials on the effect of glycerine on meat quality have yet to be analysed, other studies suggest that the inclusion of glycerol can improve pig meat quality by reducing drip loss  and increase breast yield in broilers by improving protein deposition .
In a 6-month study that began this month at the University of Missouri-Columbia, Monty Kerley, professor of ruminant nutrition, is examining the effectiveness of glycerin (0, 5, 10 or 20%) as cattle feed using 60 calves from various breeds. In addition to monitoring feeding limits and growth patterns, glycerine metabolism in cattle will also be studied. Kerley sees the use of glycerine as cattle feed as a short-term option as he believes in time newer industrial applications for glycerine could price it out of the animal feed industry.
Thus glycerol appears to have promise as an energy source in animal diets. However, more studies are needed about the quality of glycerol from biodiesel production before its use can be recommended in animal feeds.
The CAB Abstracts database contains the abstracts of several papers on the use of glycerine in livestock diets.
 Kijora C, 1996. Utilization of glycerol as a byproduct of "Biodiesel" production in animal nutrition. Landbauforshung Volkenrode 169:151-157.
 Kijora C, Bergner H, Kupsch RD, Hagemann L, 1995. Glycerol as a feed component in fattening pigs. Archiv fur Tierernahrung 47:345-360.
 Kijora C, Kupscy RD, Bergner H, Wenk C, Prabucki AL, 1997. Comparative investigation on the utilization of glycerol, free fatty acids, free fatty acids in combination with glycerol and vegetable oil in fattening of pigs. Journal of Animal Physiology and Animal Nutrition 77:127-138.
 Kuhn M, 1996. Use of technical rapeseed-glycerol from Biodiesel production in the fattening of pigs. Landbauforshung Volkenrode 169:163-167.
 Mourot J, Aumaitre A, Mounier A, Peiniau P, Francois AC, 1994. Nutritional and physiological effects of dietary glycerol in the growing pig. Consequences on fatty tissues and post mortem muscular parameters. Livestock Production Science 38:237-244.
 Schröder A, Südekum K-H, 1999. Glycerol as a by-product of biodiesel production in diets for ruminants. 10th International Rapeseed Congress, Canberra, Australia. 6 pp. http://www.regional.org.au/au/gcirc/1/241.htm Accessed 31 May 2007.
 Simon A, Bergner H, Schwabe M, 1996. Glycerol as a feed component for broiler chickens. Archiv fur Tierernahrung 49:103-112.
 Simon A, Schwabe M, Bergner H, 1997. Glycerol supplementation to broiler rations with low crude protein content. Archives in Animal Nutrition 50:271-282.
 Cerrate S, Yan F, Wang Z, Coto C, Sacakli P, Waldroup PW, 2006. Evaluation of glycerine from biodiesel production as a feed ingredient for broilers. International Journal of Poultry Science 5:1001-1007.
Suggested further reading
Niles D, 2006. Combating the glycerine glut. Biodiesel 3:38-44. http://www.biodieselmagazine.com/article.jsp?article_id=1123 Accessed 31 May 2007.
Van Heugten E, 2007. Byproducts from energy production for swine. Swine News May 2007. North Carolina State Swine Extension, p. 2-4. http://mark.asci.ncsu.edu/Swine_News/2007/sn_v3004%20(May).htm Accessed 31 May 2007.
Waldroup PW, 2007. Biofuels and broilers - competitors or cooperators? Proceedings of the 5th Mid-Atlantic Nutrition Conference 2007, Zimmermann NG, ed, University of Maryland, Maryland, USA. http://www.ddgs.umn.edu/articles-poultry/2007-Waldroup-%20Biofuels%20and%20broilers%20(MANC).pdf Accessed 31 May 2007.