Biofuel co-products as livestock feed - Opportunities and challenges

Feeding biofuels co-products to pigs 183(Fastinger and Mahan, 2003). The underlying mechanism isthat large feedstuff particles provide less surface area perunit of mass for digestive enzymes to interact with theirsubstrates (Goodband, Tokach and Nelssen, 2002). Nutrientdigestibility for larger particles is therefore lower than forsmaller particles, because nutrient digestion is limited toa specific time interval due to digesta transit through thegastro intestinal tract.Opportunities may exist to grind DDGS to increasenutrient digestibility, because the mean particle size ofDDGS varies widely among samples. For example, themean particle size of unground maize DDGS ranged from434 to 949 μm from dry-grind ethanol plants (Liu, 2008).Mendoza et al. (2010c) evaluated DDGS from 15 differentsources and observed considerable variability in particle sizeamong sources, but DE and ME content can be improvedby grinding to a smaller particle size.Reducing mean particle size from 517 to 383 μm inDDGS increased the apparent ileal digestibility and ATTDof energy in grower pigs by 2.3 and 1.3 percentage units,respectively (Yáñez et al., 2011). Liu et al. (2011b) showedan even greater response for improving ME of DDGS byreducing particle size, where each 25-micron decrease inDDGS particle size (from 818 µm to 308 µm), resulted ina ME contribution from DDGS to the diet of 13.6 kcal/kgDM, but diet flowability was reduced. Combined, grindingof DDGS will have more of a positive impact on nutrientdigestibility on the DDGS sources with a mean particle sizegreater than 660 μm (Liu, 2008), and mean particle sizeshould be measured routinely in feed quality evaluation.Hydrothermal processingUnlike grinding, which is common for all dry feed, not allmonogastric feed is subjected to hydrothermal processing(Hancock and Behnke, 2001). Steam pelleting of feed iscommon in some parts of the United States and WesternEurope, whereas mash feeding is common in westernCanada and Australia. The impact of pelleting on nutrientdigestibility of maize co-products is not clear, but it appearsto improve nutrient digestibility. Growth performance andnutrient digestibility was improved when nursery pigs werefed diets containing 30 percent maize DDGS (Zhu et al.,2010). Pelleting of diets containing high levels of maize fibre(maize gluten feed) improved N balance, apparently due tothe increased availability of tryptophan (Yen et al., 1971).Extrusion subjects feed to heat and pressure moreextensively than steam pelleting, and can open the physicalstructure of the feedstuff matrix (Hancock and Behnke,2001). Extrusion processing is common for aquacultureand pet feed, because fish and companion animals havegenerally much lower nutrient digestibility of plant-basedfeeds than swine and poultry. Therefore, extrusion isrequired to achieve suitable feed management characteristics.However, very little is known about the effects ofextruding maize and maize co-products on nutritional valuefor swine (Muley et al., 2007). In broiler chicks, extrusion ofDDGS from triticale, wheat and maize improved energy andamino acid digestibility (Oryschak et al., 2010a, b). In contrast,extrusion of DDGS from wheat and maize increasedenergy digestibility for both in pigs, perhaps, in part, byenhancing nutrient digestibility of residual starch in DDGS,but also by improving amino acid digestibility in maizeDDGS (Beltranena et al., 2009). These results indicate thateffects of extrusion processing on nutrient digestibility willbe specific to source of DDGS and species targeted.Supplemental enzymesThe addition of exogenous enzymes to animal feeds toimprove nutrient digestion is not a new concept, andresponses have been reviewed in detail (Chesson, 1987;Bedford, 2000). The majority of commercial enzyme productshave been targeted toward poultry (Annison andChoct, 1991; Cowan, 1993) and are typically added to dietscontaining barley, oats, peas, rye or wheat (Aimonen andNasi, 1991; Thacker, Campbell and GrootWassink, 1992;Viveros et al., 1994; Hubener, Vahjen and Simon, 2002),with only limited research evaluating enzyme use in maizesoybeanmeal diets (Saleh et al., 2005).The introduction of larger quantities of co-products,such as DDGS, into swine diets will increase the dietary contentof fibre. The negative effects on energy and nutrientdigestibility, and ultimately animal performance, from feedingsuch diets may be reduced partly by using supplementalenzymes (Zijlstra, Owusu-Asiedu and Simmins, 2010).Detailed chemical characterization of fibre components inDDGS indicates that it contains arabinoxylan constituents,which is one potential substrate for supplemental fibredegradingenzymes, and that some intact phytate remainsas substrate for supplemental phytase (Widyaratne andZijlstra, 2007; Liu, 2011). However, results from a recentstudy by Kerr, Weber and Shurson (2011) showed minimaleffects on nutrient digestibility, and no improvement ingrowth performance, from supplementing with ten differentcommercial enzyme products and additives in nurseryor finishing pig diets containing 30 percent DDGS.PhytasePlant-based phytate is well known for its ability to bindP and other nutrients and thereby reduce digestibility ofthese nutrients (Oatway, Vasanthan and Helm, 2001).The phytate contained in the grain is partly transformedduring the fermentation process to produce ethanol andco-products. Intact phytate (inositol hexaphosphate) does,unlike nutrients other than starch, not concentrate 2 to 3fold in the DDGS, but is instead partially hydrolyzed intoinositol phosphates, which contain 5 or fewer P molecules