Digestible and metabolizable energy content of crude glycerin originating from different sources in nursery pigs.

The energy value of crude glycerin from different biodiesel production facilities was determined in nursery pigs (initial BW of 10.4 kg) to predict apparent DE and ME based on the composition of crude glycerin. 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, 2 glycerin products were supplemented at either 7.7 or 6.9%. In addition, soybean oil and lard were included at 6.7% as 2 dietary treatments to serve as positive controls. Each diet was fed twice daily to pigs in individual metabolism crates. After a 6-d adjustment period, a 4-d balance experiment was conducted. During the collection period, feces and urine were collected daily and stored at 0 degrees C until analysis. The GE of each test ingredient and diet and of urine and fecal samples from each pig were determined by isoperibol bomb calorimetry. The DE and ME values of crude glycerol were estimated by difference, whereby 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 US Pharmacopeia grade glycerin were determined to be 4,325, 4,457, and 3,682 kcal/kg, respectively. In contrast, GE of the crude glycerin samples ranged from 3,173 to 6,021 kcal/kg, DE ranged from 3,022 to 5,228 kcal/kg, and ME ranged from 2,535 to 5,206 kcal/kg, reflecting the content of glycerol, methanol, and FFA in the crude glycerin. The GE, DE, and ME of soybean oil and lard were determined to be 9,443, 8,567, and 8,469 kcal/kg, and 9,456, 8,524, and 8,639 kcal/kg, respectively. The stepwise regression prediction of the ME in crude glycerin exhibited R(2) of only 0.41 [ME, kcal/kg (as-is basis) = (37.09 x % of glycerin) + (97.15 x % of fatty acids)], whereas prediction of GE achieved an R(2) of 0.99 [GE, kcal/kg (as-is basis) = -236 + (46.08 x % of glycerin) + (61.78 x % of methanol) + (103.62 x % of fatty acids)]. On average, the ME of crude glycerin was 85.4% of its GE (SE 5.3) and did not differ by glycerin source. The data provided in these experiments indicate that crude glycerin is a valuable energy source, with its GE concentration dependent on the concentration of glycerin, methanol, and fatty acids, and with ME as a percentage of GE averaging 85.4%.