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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #234437

Title: Digestible and Metabolizable Energy Content of Crude Glycerin Originating from Different Sources in Growing Pigs

item Kerr, Brian
item Weber, Thomas

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2009
Publication Date: 12/1/2009
Citation: Kerr, B.J., Weber, T.E., Dozier III, W.A., Kidd, M.T. 2009. Digestible and Metabolizable Energy Content of Crude Glycerin Originating from Different Sources in Growing Pigs. Journal of Animal Science. 87:4042-4049.

Interpretive Summary: The expansion of the biodiesel industry has generated substantial amounts of crude glycerol (the principal co-product of biodiesel production) which, due to availability and price, has become available for use as a livestock feedstuff. Crude glycerin has been shown to be a viable source of energy for swine and poultry diets, but data is lacking on the variation in energy value of crude glycerin for growing pigs, due to the source and composition of crude glycerin. This research demonstrated that the concentration of glycerin, free fatty acids, and methanol contained in crude glycerin directly affects the metabolizable energy value in pigs, ranging from 2,535 to 5,206 kcal/kg. This information is important for nutritionists at universities, feed companies, and swine production facilities for the determination of the energy value of crude glycerol for use in feed formulations, and provides a basis from which to assess its economic value.

Technical Abstract: Apparent digestible (DE) and metabolizable (ME) of various crude glycerins from different biodiesel production facilities were empirically determined in nursery pigs (10.4 kg initial body weight) in order to predict the DE and ME based on crude glycerin composition. Dietary treatments consisted of a basal diet or diets containing crude glycerin from various biodiesel production facilities supplemented in the diet at approximately 9.1%. Because of bulk density differences, two glycerin sources were supplemented at either 7.7 or 6.9%. In addition, soybean oil and lard were included (6.7%) as dietary treatments to serve as positive controls. Each diet was fed twice daily to pigs in individual metabolism crates. After a 6-day adjustment period, a 4-day balance trial was conducted. During the collection period, feces and urine were collected daily and stored at 0°C until analyses. The gross energy (GE) of each test ingredient, diet, and urine and fecal samples from each pig were determined by isoperibol bomb calorimetry. Digestible energy of the diet was calculated by subtracting fecal energy from the GE in the feed, whereas ME was calculated by subtracting the urinary energy from DE. The DE and ME values of crude glycerol were estimated by difference where the DE and ME content of the basal diet was subtracted from the complete diet containing the test ingredient. Gross energy, DE, and ME of USP-grade glycerin was calculated to be 4,325, 4,443, and 3,664 kcal/kg, respectively. In contrast, GE of the crude glycerin samples ranged from 3,173 to 6,021, DE from 3,022 to 5,228, and ME from 2,535 to 5,206 kcal/kg, reflecting the content of glycerol, methanol, and free fatty acids in the crude glycerin. The GE, DE, and ME of soybean oil and lard was determined to be 9,443, 8,567, 8,469, and 9,424, 8,543, and 8,639 kcal/kg, respectively. The stepwise regression prediction of the ME in crude glycerin exhibited R-square of only 0.42, whereas prediction of GE achieved a R-square of 0.99. On average, the ME of crude glycerin was 85.4% of its GE (SD 17.2) and did not differ by glycerin source. Data provided in these experiments indicate that crude glycerin is a valuable energy source with its energy concentration dependent upon the concentration of glycerin, methanol, and fatty acids.