Biofuel co-products as livestock feed - Opportunities and challenges

416Biofuel co-products as livestock feed – Opportunities and challengesTABLE 8Summary of studies evaluating the effects of feeding glycerol to different fish speciesFish speciesGlycerolinclusionIngredientreplacedOptimum(%) a Flesh composition ReferenceChannel catfish(Ictalurus punctatus)Rainbow trout(Oncorhynchus mykiss)0-20 Maize 10 Fillet fatdecreased0-12 WheatmiddlingsLi et al., 2010b (1)– No difference Menton, Slinger and Hilton,1986 (2)Notes: Optimum determined based on growth gain and feed efficiency as similar or superior to a Control diet. (1) Glycerol from biodiesel production.(2) Free glycerol included in low energy diets compared with a diet with similar energy density.to 0.015 percent (150 ppm) in the final animal feed (FDA,2006). Because the boiling point of methanol is 64.4 °C(Lide, 2001), it is believed that extrusion processing,commonly used in preparing fish feed, could eliminate anyresidual methanol found in crude glycerine. The colour ofcrude glycerine can range from clear to dark, reflectingpigments and compounds found in the parent feedstock.Feeding value of crude glycerine to fishThere has apparently been only one published study(Table 8) that has evaluated the use of crude glycerinefrom the biodiesel industry in fish (Li et al., 2010b). Thisstudy used crude glycerine as a source of energy to replacemaize meal in the diet of channel catfish. They determinedthat a level of 10 percent was optimal for weight gainand feed efficiency; fillet fat content decreased at levels inexcess of 5 percent. Pure glycerol was evaluated in anotherstudy in rainbow trout (Menton, Slinger and Hilton, 1986).Replacing wheat middlings by free glycerol up to 12 percentof the diet resulted in comparable weight gain, feedefficiency and carcass composition as fish fed a diet withsimilar energy density. The authors also found that glycerolcan be an effective precursor for gluconeogenesis, but notfor lipogenesis; however, rainbow trout cannot efficientlyutilize glucose as a source of energy.CRUDE GLYCERINE ISSUES, CHALLENGES,KNOWLEDGE GAPS AND RESEARCH NEEDSStudies in other monogastric species suggest that crudeglycerin can be a viable energy source. However, consideringthe current level of research in fish nutrition, which isessentially non-existent, an optimum level can not be recommendedat this time. More studies are required to determinethe efficacy of crude glycerol in major species such astilapia, channel catfish, rainbow trout and yellow perch. Aswith other co-products, variability is an issue that hindersthe use of crude glycerin in aquafeeds. Residual methanolis a potential safety hazard that needs to be addressed aswell. Considering the physical characteristics of crude glycerin,other issues that should be evaluated include extrusionprocessing behaviour, handling and storage characteristics,potential corrosive effects, and the effect of feeding glycerinon flesh quality and health of fish.CONCLUSIONSDDGS and glycerine, co-products from the fuel ethanol andbiodiesel industries, respectively, appear to be viable alternativefeed ingredients for aquafeeds. DDGS is best usedto replace a portion of SBM and maize in the diet. Becauseof variability issues and inherent nutritional limitations ofDDGS, an inclusion level of up to 20 percent appears to besafe for most omnivorous fish species, whereas 10–15 percentis recommended for carnivorous fish such as rainbowtrout. Specifically, DDGS can effectively be included at concentrationsof 20 to 40 percent for channel catfish, tilapiaand yellow perch, but at lower concentrations (10–15 percent)for rainbow trout, bass and some crustacean species.Nonetheless, when economically viable, supplementationwith lysine will allow for higher DDGS inclusion rates. It hasalso been shown that DDGS can be included at high concentrations(up to 40 to 60 percent) while maintaining feedquality in terms of water stability and pellet durability whenDDGS is part of extruded aquafeeds. Interestingly, the optimalinclusion level of DDGS in aquafeeds for superior pelletquality appears to be around 20 percent, which coincideswith optimal fish performance in most species. In some species,nutritional characteristics of the final products can bealtered. Lower protein and higher fat contents are usuallyobserved when feeding DDGS above optimal levels. Theefficacy of crude glycerine in fish diets is less evident. Verylimited information suggests that glycerine might be usedas an energy source. However, comprehensive investigationis still needed to address the use of glycerol as a feed ingredientfor major fish species. The effect of glycerol on feedprocessing, final product quality, metabolism and healthof fish are some areas that needs further research beforeglycerine can be efficiently and safely used in aquafeeds.Biofuels will clearly continue to play a key role in the globalenergy portfolio over the coming years, and co-productssuch as DDGS, glycerine, as well as other new co-productsyet to be developed, will continue to grow in quantity.Aquafeeds may be a viable opportunity for their utilization.BIBLIOGRAPHYAbo-state, H.A., Tahoun, A.M. & Hammouda, Y.A. 2009.Effect of replacement of SBM by DDGS combined withcommercial phytase on Nile tilapia (Oreochromis niloticus)