Biofuel co-products as livestock feed - Opportunities and challenges

184Biofuel co-products as livestock feed – Opportunities and challenges(Widyaratne and Zijlstra, 2007). Digestibility of P is thereforehigher in DDGS than in the feedstock grain. Still, sufficientphytate in DDGS remains to hinder P digestibility. Indeed,the addition of 500 FTU (phytase units) of phytase to amaize starch diet containing 44 percent DDGS increasedthe ATTD of energy of P in the diet by 10.5 percentageunits, but did not affect energy and amino acid digestibility(Yáñez et al., 2011). However, data on the impact ofphytase, with or without other enzymes, on nutrient (andenergy) digestibility in maize co-product diets is lacking andinconsistent. While addition of 500 units phytase improvedP digestibility in diets containing 20 percent DDGS in starteror finisher pigs, it did not improve DM digestibility (Xu,Whitney and Shurson, 2006a, b). In contrast, Lindemannet al. (2009) reported that pigs fed diets containing 20 percentDDGS supplemented with 250 or 500 U/kg phytaseexhibited greater DM, energy, and N digestibility thanunsupplemented pigs, but there were no further improvementsin faecal DM, energy or N digestibility with additionalxylanase supplementation. Therefore, even though DDGShas a higher P digestibility than grain and protein meals,supplemental phytase may provide additional benefits indiets containing DDGS.Fibre-degrading enzymesThe negative impact of fibre or non-starch polysaccharideshas been described for cereal grains, including barley andwheat (Fairbairn et al., 1999; Zijlstra et al., 2009). The positiveeffects of fibre-degrading enzymes on energy digestibilityof wheat have been defined, as long as the supplementalenzyme matches with a substrate that limits nutrientutilization or animal performance (e.g. Mavromichalis etal., 2000; Cadogan, Choct and Campbell, 2003; Barreraet al., 2004). Thus, not surprisingly, diets containing wheatco-products from flour milling (co-products that have beensubjected to limited processing during production) have adrastically increased non-starch polysaccharide content andhence arabinoxylan content, and supplemental xylanaseimproved energy digestibility in swine (Nortey et al., 2007,2008). Combined, these results indicate that wheat fibre inits native form is a good substrate for supplemental xylanasein swine diets.Interestingly, the relationship between co-products fromethanol production (maize or wheat DDGS) and the potentialbenefits from supplemental xylanase is less clear. Studieshave shown no improvement in growth performance fromadding enzymes to maize DDGS diets for nursery pigs(Jones et al., 2010), while studies by Spencer et al. (2007)and Yoon et al. (2010) showed improvements from theuse of enzymes in nursery and in grower-finisher diets,respectively. Additional studies have also shown improvementsin nutrient digestibility when enzymes are added toDDGS diets (Jendza et al., 2009; Yoon et al., 2010; Feoli etal., 2008d), but improvements in nutrient digestibility donot always result in improvements in growth performance(Kerr, Weber and Shurson, 2011). Because DDGS has beensubjected to extensive periods in solution, followed by drying,adding supplemental xylanase to DDGS diets does notalways seem to improve energy digestibility of wheat DDGS(Widyaratne, Patience and Zijlstra, 2009; Yáñez et al., 2011)or maize DDGS (Mercedes et al., 2010), although positiveexamples exist (Lindemann et al., 2009). Furthermore,xylanase supplementation did not improve growth performancein nursery pigs fed diets containing 30 percent maizeDDGS (Jones et al., 2010), although xylanase improvedgrowth performance and digestibility of diet componentsin broilers (Liu et al., 2011a). Finally, supplementation ofa multi-enzyme complex to diets containing wheat DDGSimproved growth performance and nutrient digestibilityin finisher pigs (Emiola et al., 2009), although the barleyand maize contained in the diets used might have alsointeracted with the multi-enzyme to provide the positiveresponse, and the multi-enzyme complex may be requiredto open the fibre matrix.The more extensive processing used during ethanolproduction compared with flour milling might thus havecaused changes in the feedstuff matrix that may makesupplemental enzymes less advantageous for improvingnutrient digestibility. These differences in enzyme responsesmay be due to fibre-degrading enzymes that can be addedduring the ethanol production process to enhance ethanolyield, making the regular substrate for these supplementalenzymes not the limiting factor for nutrient digestibility.Feedstuffs and enzyme selection require proper characterizationto ensure that the substrates and enzymes match,and that the substrate is indeed the critical factor thathinders nutrient digestibility.IN VITRO ENERGY DIGESTIBILTY IN DDGSNutritional value of DDGS is known to vary substantiallyamong sources (Nuez Ortín and Yu, 2009; Stein andShurson, 2009; Zijlstra and Beltranena, 2009). Specifically,the ATTD of energy ranged from 74 to 83 percent formaize DDGS (Pedersen, Boersma and Stein, 2007a) andfrom 56 to 76 percent for wheat DDGS (Cozannet et al.,2010). Prediction of quality of DDGS prior to feed processingis thus an important component of reducing the riskof less predictable animal performance when using DDGSin animal feeds. In vitro energy digestibility techniques canbe used to screen ranges in energy digestibility amongfeedstuff samples and thereby support the development offeedstuff databases and rapid feed quality evaluation systemssuch as near-infrared reflectance spectroscopy (Zijlstra,Owusu-Asiedu and Simmins, 2010).In vitro digestibility techniques using enzymes and incubationperiods that mimic in vivo digestion can predict with