Biofuel co-products as livestock feed - Opportunities and challenges

94Biofuel co-products as livestock feed – Opportunities and challenges(DM basis) with a range of 5 to 50 percent of the diet(Vasconcelos and Galyean, 2007). In the United States CornBelt, survey data suggest that beef producers feeding DGShave an average dietary inclusion of 22 to 31 percent on awet basis (approximately 15 to 20 percent of DM) (NASS,2007). Respondents to both a feedlot nutritionist survey(Vasconcelos and Galyean, 2007) and a Nebraska feedlotindustry survey (Waterbury et al., 2009) reported that DGSare the most common ethanol co-product used by cattlefeeders. The Nebraska survey indicates 53 and 29 percentof Nebraska feedlots feed WDGS and MDGS, respectively.The nutritionist survey indicated 69 percent of the 29 nutritionistswere feeding DGS as the primary co-product inthe diet, and these beef nutritionists were responsible forformulating diets for nearly 70 percent of cattle on feed inthe United States. Feeding values of the DGS co-productsrelative to maize were calculated for each feedlot inclusionlevel of WDGS, MDGS and DDGS from measured biologicalfeed efficiency values. These feeding values decrease asthe level of co-product increases in the diets. Thus, as moreDGS is included in the diet, it replaces less maize per unitincrease in the substitution rate. In addition, the relativefeeding value of DDGS declines at a faster rate than WDGSas inclusion levels increase, indicating that WDGS has ahigher feeding value than DDGS.For cattle, DGS inclusion in diets improves growth ratesand thus reduces time in the feedlot for finishing cattle byseveral days, depending on the inclusion level and whetherthe DGS are fed dry or wet. Less time in the feedlot forfinished cattle reduces fuel use for transportation of feedas well as methane emissions from enteric fermentation.Enteric methane production is calculated from cattle size,projected DMI, and energy content of the diet. Feed inputsare used to calculate gross energy intake by the cattlewith standard animal energy equations (NRC, 1996). Anaverage 2.9 percent of gross energy is lost as enteric fermentationmethane by feedlot cattle (see BESS 2009.4.0User’s Guide, http://nutechmarketplace.com/shoppingcart/products/BESS.html). Due to a lack of data on comparisonof enteric methane production between DGS and maizebaseddiets, the two feedstuffs were assigned the samemethane production potential on a DM basis.The feeding values of WDGS, MDGS and DDGS, whenfed at 20 to 40 percent of diet DM, were 143 to 130 percent,124 to 117 percent, and a constant 113 percent ofmaize (DM basis), respectively. The feeding value of DGSdecreased as moisture level decreased. The feeding valueof WDGS and MDGS decreased as inclusion level increased.The feeding value of DDGS was a constant 113 percent ofmaize DM. All scenarios evaluated had ethanol life-cycleemissions less than gasoline (Table 24). Low inclusion levelsof DGS had greater reduction of GHG emissions than higherinclusion levels. This is influenced by regional variabilityTABLE 24Percentage reduction in greenhouse gas (GHG) emissionsfor an equivalent quantity of energy from ethanol relativeto gasoline when accounting for wet (WDGS), modified(MDGS) and dried distillers grains (DDGS) moisture contentand dietary inclusion levelBeef CattleDGS, % of diet DM 10 20 30 40WDGS, GHG % reduction to 62.4 60.6 58.4 56.7gasoline (1)MDGS, GHG % reduction to 53.9 52.6 50.9 49.7gasoline (1)DDGS, GHG % reduction togasoline (1) 46.1 45.4 44.4 43.9Notes: (1) Gasoline reference point is 97.7 g CO 2eqv/MJ (Liska andPerrin, 2009). Source: Adapted from Bremer et al., 2011.in GHG emissions from both crop and livestock production(Bremer et al., 2010b).Feeding DGS to livestock contributes to the environmentalbenefit of fuel ethanol relative to gasoline. TheGHG emissions benefits of ethanol are determined byhow DGS moisture is managed at the ethanol productionfacility and what animal classes are fed. Ethanol productionfacilities producing DDGS require 167 percent of theenergy and produce 145 percent of the GHG emissions ofethanol production facilities producing WDGS (Liska et al.,2009). Feeding WDGS to feedlot cattle within 100 km ofan ethanol plant resulted in the greatest reduction of GHGemissions. Cattle performance is improved with WDGS,and locating the ethanol plant close to feedlots minimizestransportation of feed co-products, which reduces costsand emissions. Not drying the DGS also reduces costs andemissions for the ethanol plant, as well as improving feedlotcattle performance compared with DDGS or a maize baseddiet.NEW DEVELOPMENTSImpact of grain feedstock use for ethanolIn the United States, maize is the primary grain used forethanol production. Grain sorghum [milo], wheat and triticalehave also been used in some locations, such as WesternCanada, where maize is less readily available. Maize andsorghum have similar amounts of starch and therefore havesimilar ethanol yields. Al-Suwaiegh et al. (2002) comparedsorghum and maize DGS produced at the same ethanolplant and found the maize DGS to have 10 percent greaterfeeding value. Galyean and Vasconcelos (2007) reportedstatistically similar responses in G:F for sorghum and maizeDGS (0.169 and 0.176, respectively), but the feeding valueof maize DGS was 25 percent greater than sorghum DGS.Mustafa et al. (2000) found that wheat DGS has moreNDF and less fat, but more degradable protein, than maizeDGS. Walter et al. (2010) compared wheat and maize DGSat 20 percent and 40 percent of diet DM in a barley-based