Biofuel co-products as livestock feed - Opportunities and challenges

Utilization of co-products of the biofuel industry as livestock feeds – a synthesis 505species that are benefiting. The increased efficiency of frontendfractionation for ethanol production and the potentialfor increasing the range of co-products available are discussed(Shurson, Tilstra and Kerr, 3; Cooper and Weber, 25).Rear-end oil extraction is also possible with dry milling, theoil being available as maize oil for livestock or to contributewith other vegetable oils in biodiesel production (Shurson,Tilstra and Kerr, 3; Cooper and Weber, 1). Within the USA,Shurson, Tilstra and Kerr (3) do not foresee an immediateincrease in the number of wet milling plants, but possibly asmall increase in the number of dry grind plants.Comparisons of wet and dry processing of DGS (distillersgrain with solubles) have been inconclusive, but thereare practical considerations, such as handling and storagecosts, with the wet product having a relatively short shelflife of up to seven days (dependent on ambient temperature,unless anaerobic storage is available, such as bunkers,pits or silage bags); it is advisable to avoid vertical towerstorage because of problems of compaction and flow, creatingproblems with hygiene and auger-based mixing anddelivery systems (Kalscheur et al., 7). However, in 2007, drymills sold a third of their distillers grain with solubles wet,rather than dry (Wang and Dunn, 27). For usage close tothe plant, wet co-products avoid the costs of drying. Insome situations, heat for drying can be supplied by burningprocess residues. Sorghum bagasse (Rao et al., 12), biogasfrom sugar cane vinasse (Patino et al., 15), and from sugarcane bagasse (Anandan and Sampath, 16) are suggestedas sources of fuel.The current extraction process for ethanol necessitatesthe use of sulphuric acid, thus increasing the level of sulphurin DG above that in the original grain and creatinga potential cause of excess ruminal hydrogen sulphide(Galyean et al., 4; Schoonmaker and Beitz, 6). Sugar andstarch fermentation to produce ethanol is described byLywood and Pinkney (2), as is the hydrolysis of lingocellulosefeeds, which is then followed by fermentation togive ethanol. Both processes show high levels of efficiency.Appropriate processing plants for cellulosic materials arebeing developed (Shurson, Tilstra and Kerr, 3).Co-products resulting from ethanol productionNotwithstanding the debate regarding the use of landfor fuel rather than feed, the production of ethanol asa biofuel is the largest growth sector in the USA, wherethere are now 200 plants producing 35 million tonne ofco-products annually (Shurson, Tilstra and Kerr, 3). Mjounand Rosentrater (23) estimated ethanol production at51 billion litres in 2010, over three times as much as in 2005,with 32.9 million tonne of distillers grain being produced,of which 2.7 percent came from the beverage industryand the remainder from maize-based ethanol production.Currently, in the USA, the beef industry uses 66 percentof the available DDGS, the dairy industry 14 percent, pigs8 percent and poultry 12 percent, with little evidence ofmeaningful amounts being used in aquaculture (Mjounand Rosentrater, 23). However, the authors note substantialincreases in the amount of fish coming from aquacultureduring the last decade, coupled with the high price of thetraditional protein sources, fishmeal and soybean meal, andthe comparatively low price of DDGS.In Western Canada, the current annual demand forDDGS is estimated at 1.4 million tonne, but the localindustry, based on wheat, can only produce around halfa million tonne, the shortfall being met from the USA(Christensen et al., 26). In Europe, the dominant feedstockfor ethanol production is also wheat, although some othercereals, especially barley, may be added to the mix (Noblet,Cozannet and Skiba, 9). Rye is also used as a feedstock,but is restricted to colder areas (Kalscheur et al., 7). Theproducts of fermentation are expected to be 93 percentethanol, 3 percent yeast and 4 percent glycerol (Noblet,Cozannet and Skiba, 9). Distillers grain from variousfeedstocks can be mixed with minimal changes in animalperformance responses, although Kalscheur et al. (7) ratebarley as the least productive cereal feedstock, because ofthe relatively high fibre and low starch content of the grain.Shurson, Tilstra and Kerr (3) address food safety andnote possible causes of contamination resulting from theprocess, including excess sulphur, mycotoxins (in adverseclimatic conditions, especially excessive heat or moisture),harmful bacteria, and transfer of antibiotics to animaland human tissue. The formation of H 2 S and the dangersit represents to both ruminants and non-ruminants aredescribed by Schoonmaker and Beitz (6), who considerthat it rivals cyanide in its toxicity. Endogenous H 2 S isproduced by the catabolism of S-containing amino acids,cysteine being important in this process, or by sulphatereducingbacteria present in the digestive tract. But itis important to note that added sulphur used in thefermentation process is the primary culprit for ruminallyproduced hydrogen sulphide, not the dietary S-containingamino acids. At low levels, H 2 S functions as a gaseoussignalling molecule in animal tissues; at higher levels itinhibits oxidative processes in nervous tissue, which inruminants can lead to a disorder of the nervous systemknown as polioencephalomalacia (PEM) (Schoonmaker andBeitz, 6).Co-products from sweet sorghum processed in thedecentralized system being promoted in India are the grain,bagasse, foam and froth, steam and vinasse (Rao et al.,12). The grain produced in the wet season is often mouldyand unsuitable for human consumption and therefore usedfor alcohol production and livestock feed (there are threegrowing seasons per year); the bagasse can be used as afeed, either fresh or after ensiling; as fuel for a variety of