Biofuel co-products as livestock feed - Opportunities and challenges

186Biofuel co-products as livestock feed – Opportunities and challengesof its GE (Brambilla and Hill, 1966; Lin, Romsos and Leveille,1976; Rosebrough et al., 1980; Cerrate et al., 2006), butthere have been no empirical determinations of the ME ofcrude glycerin in swine until recently.Bartlet and Schneider (2002) reported ME values ofrefined glycerin in 35-kg pigs and determined that theME value of glycerin decreased as the level of dietary glycerinincreased (4189, 3349 and 2256 kcal/kg at 5, 10 and15 percent inclusion levels, respectively) with an averagevalue of 3292 kcal/kg on an as-is basis. Because pre-caecaldigestibility of glycerin was determined to be approximately97 percent (Bartlet and Schneider, 2002), the observeddecrease in ME value may be a result of increased bloodglycerol levels following glycerin supplementation (Kijoraet al., 1995; Kijora and Kupsch, 2006; Simon, Bergnerand Schwabe, 1996), suggesting that complete renal reabsorptionis prevented and glycerol excretion in the urineis increased (Kijora et al., 1995; Robergs and Griffin, 1998).In nursery and finishing pigs, Lammers et al. (2008a)determined that the ME content of a crude glycerin coproductcontaining 87 percent glycerin was 3207 kcal/kg, and did not differ between pigs weighing 10 or100 kg (Table 7). Based strictly on its glycerin content,this equates to 3688 kcal ME/kg on a 100 percent glycerinbasis (3207 kcal ME/kg/87 percent glycerin), which isslightly lower than the 3810 kcal ME/kg (average of the5 and 10 percent inclusion levels) reported by Bartlet andSchneider (2002), but similar to the 3656 kcal ME/kg asreported by Mendoza et al. (2010a) using a 30 percentinclusion level of glycerin.Similar to data reported by Bartlet and Schneider(2002), increasing crude glycerin from 5 to 10 to 20 percentin 10-kg pigs (Lammers et al., 2008a) quadraticallyreduced ME content (3601, 3239 and 2579 kcal ME/kg,respectively), suggesting that high dietary concentrationsof crude glycerin may not be fully utilized by 10-kg pigs.In contrast, dietary concentrations of crude glycerin had noeffect on ME determination in 100-kg pigs (Lammers et al.,2008a). The ratio of DE:GE is an indicator of how well acrude glycerin source is digested, and for the crude glycerinsource evaluated by Lammers et al. (2008a), it equalled92 percent, suggesting that crude glycerin is well digested,being only slightly lower that the 97 percent of glycerindigested before the caecum, as reported by Bartlet andSchneider (2002). In addition, the ratio of ME:DE indicateshow well energy is utilized once digested and absorbed.For the crude glycerin source evaluated by Lammers et al.(2008a), the ratio was 96 percent, which is identical to theME:DE ratio for soybean oil, and is comparable to the ratioof ME:DE (97%) for maize grain (NRC, 1998), all of whichsupport the assertion that crude glycerol is well utilized bythe pig as a source of energy.Chemical composition variabilitySimilar to other co-products used to feed livestock, thechemical composition of crude glycerin can vary widely(Thompson and He, 2006; Kijora and Kupsch, 2006;Hansen et al., 2009; Kerr et al., 2009). The consequencesof this variable chemical composition in crude glycerinrelative to its energy value for animals have not been welldescribed. Recently, 10 sources of crude glycerin from variousbiodiesel production facilities in the United States wereevaluated for energy utilization in growing pigs (Table 8).The crude glycerin sources originating from biodieselplants using soybean oil averaged 84 percent glycerin, withminimal variability noted among 6 of the sources obtained.Conversely, crude glycerin sources obtained from biodieselplants using tallow, yellow grease or poultry oil as initial lipidfeedstock ranged from 52 to 94 percent glycerin. The crudeglycerin co-products derived from either non-acidulated yellowgrease or poultry fat had the lowest glycerin content,but also had the highest free fatty acid concentrations. Thehigh fatty acid content of the non-acidulated yellow greaseproduct was expected because the acidulation processresults in greater separation of methyl esters, which subsequentlyresults in a purer form of crude glycerin containingless free fatty acids (Ma and Hanna, 1999; Van Gerpen,2005; Thompson and He, 2006). In contrast, the relativelyhigh free fatty acid content in the crude glycerin obtainedfrom the biodiesel plant utilizing poultry fat as a feedstockis difficult to explain because details of the production processwere not available. Moreover, these two crude glycerinco-products (derived from non-acidulated yellow greaseand poultry fat) had higher methanol concentrations thanTABLE 7Digestible and metabolizable energy of crude glycerin fed to pigs, as-is basisTrial Pigs Initial BW (kg) DE (kcal/kg) SEM ME (kcal/kg) SEM1 18 11.0 4,401 282 3,463 4802 23 109.6 3,772 108 3,088 1183 19 8.4 3,634 218 3,177 2514 20 11.3 4,040 222 3,544 2375 22 99.9 3,553 172 3,352 192Notes: All experiments represent data from 5-day energy balance experiments following a 10-day adaptation period (Lammers et al., 2008a); BW = bodyweight; DE = digestible energy, ME = metabolizable energy; SEM = Standard Error of the Mean. Trial 1 included pigs fed diets containing 0, 5 and 10%crude glycerin. Trial 2 included pigs fed diets containing 0, 5, 10 and 20% crude glycerin. Trials 3, 4 and 5 included pigs fed diets containing 0% and10% glycerin.