Biofuel co-products as livestock feed - Opportunities and challenges

Utilization of co-products of the biofuel industry as livestock feeds – a synthesis 503Renewable Fuel Standard (RFS) in 2005, which led to theEnergy Independence and Security Act of 2007 that setstargets for blending of biofuels with fossil fuels throughto 2022 (Cooper and Weber, 1). In Europe, GHG emissionshave been reduced in all areas of activity except publicenergy production (small increase) and road transport (largeincrease) (Lywood and Pinkney, 2). By 2020, 10 percent offuels used for surface transport should come from nonfossilsources, and GHG emissions should be reduced by60 percent with a 6 percent reduction in carbon emissionscompared with 100 percent fossil fuel usage (Shurson,Tilstra and Kerr, 3). The present generation of petrolengines can tolerate 10 percent ethanol in the fuel mix.However, diesel engines currently have a maximum toleranceof 7 percent, which, because of the age of the globaltransport pool, points to a need for rapid improvement intolerance levels if the 2020 target is to be met.The feedstocks from which ethanol is produced largelyreflect the agriculture area. In the United States of America(USA), maize [corn] (Table 2) is the dominant source(Shurson, Tilstra and Kerr, 3). The USA has also built anexport trade in dried distillers grain with added solubles(DDGS), initially to Canada for beef production, but nowexpanded to a wider market, with an emphasis on pigand poultry production (Shurson, Tilstra and Kerr, 3). Thedevelopment of wet processing encouraged the siting ofplants near beef feedlots to minimize costs of drying andtransporting distillers grain. This also encouraged manybeef producers to become croppers. However, in theSouthern Great Plains of the USA, sorghum is an importantfeedstock, thus giving rise to considerable quantities of coproducts(Galyean et al., 4). In Europe (Hippenstiel et al.,11; Noblet, Cozannet and Skiba, 9) and parts of Canada(Christensen et al., 26) the major cereal contributing to theindustry is wheat. Christensen et al. (26) have traced thedevelopment of the ethanol industry in Western Canadafrom the beginning, when DDGS was imported from theUSA, to the present time. Although imports are still important,locally grown Canadian wheat is now contributingsignificantly to the distillers grain market.Other cereals – triticale, barley and rye – can be used,either alone or in combination, but are not significantethanol feedstocks compared with maize and wheat. TheEuropean targets for biofuel production will be met mainlythrough increased crop yields and continuing cropping ofarable land that should have been released from use. Theincreased availability and use of co-products in livestockfeed would partially replace a mixture of EU cereals andimported soyabean meal (Lywood and Pinkney, 2).Sugar cane and other non-cereal feedstocksSugar cane (Table 2) is also a major feedstock for ethanolproduction. Patino et al. (15) estimated that, at the presenttime, on a global scale, 90 percent of ethanol output isaccounted for by maize and sugar cane. In tropical regionsof Central and Southern America and Asia, sugar cane isone of the most important crops, and its value as a feedstockis recognized (Anandan and Sampath, 16). Between1990 and 2009, production of sugar cane in Asia increasedby 53 percent, while the land area devoted to its growingonly increased by 34 percent, suggesting an improvementin cultivation and harvesting techniques. Two of themajor prerequisites for a successful sugar cane industryare a warm environment and water. Cooper and Webber(1) stress the importance of sugar cane as a feedstock intropical countries with a high rainfall, quoting the exampleof Brazil, where 98 percent of ethanol production comesfrom this source. The same authors estimated that in 2010,93 percent of ethanol production took place in the USA,Brazil and Europe. Other feedstocks listed by Rao et al. (12)and Cooper and Webber (1) included tropical sugar beet,sweet potato, cassava and sweet sorghum. In contrastsweet sorghum is favoured by Rao et al. (12) because ofits tolerance to a wide range of harsh conditions and thenumber of options for its use, including human food, forageand biofuel production.Sweet or forage sorghum requires 25 percent of thewater needed by sugar cane, and substantially fewergrowing days (Rao et al., 12). In the decentralized process,developed for small-scale farmers to operate at a villagelevel, they describe how crushing of the sorghum plant toobtain the juice and then boiling to concentrate this arekey actions, with the two principle co-products, or residues,being the bagasse and grain. Grain free from mould is usedfor human consumption. The juice can then go forward forethanol extraction or be retained in the village for fermentationto give a mash containing 6–10 percent ethanol.Currently, the system operates for the rainy season croponly because the needs of farmers for food and livestockfeed are more easily met from crops grown in drier weather.New and unconventional feedstocksThe feedstocks discussed above are regarded as firstgenerationcrops. One of their limitations is that they couldbe seen as being in conflict with what are regarded as theprime objectives of cropping land, namely the provisionof food and livestock feed. To combat this, and also toutilize materials traditionally regarded as unusable, there isincreasing interest in what have become known as secondgenerationfeedstocks (Shurson, Tilstra and Kerr, 3). Thesecontain large amounts of cellulose (Table 2) and include cropresidues (straws and stubble), shrubs and trees. An exampleis short rotation eucalypts grown for coppicing, whichcurrently account for less than 5 percent of cleared land inAustralia (Braid, 25). Trees can provide shade and shelterto the extent that lamb survival, especially those from twin