TY - JOUR
AU - Cecava, Michael J.
AB - Abstract The demand for animal source foods is expected to track the growth of world population. Ruminant livestock occupy a unique niche in their ability to use crop residues as feeds. The factors limiting use of crop residues for both ruminant livestock production and use for biofuels are superimposable. Biomass pretreatment strategies used in biofuels production and to improve the feeding value of crop residues and low quality forages for ruminants share significant overlap. There is potential competition for plant biomass and land use for cellulosic ethanol production and ruminant livestock production. Novel technologies being explored and developed for cellulosic ethanol production will have a direct impact on expanded use of crop residues for ruminant livestock. Changing Impact of Diversion of Crop Energy to Fuel The growing demand for liquid fuels that has accompanied a rise in global population and prosperity coupled with a recognized need for mitigation of greenhouse gas emissions has led to substantial expansion of a renewable fuel industry as a replacement for fossil-based fuels. The mandates of 36 billion gallons of biofuels by 2022 and production of 21 billion gallons of advanced biofuels from cellulosic feedstocks that are part of the U.S. Energy Independence Security Act of 2007 have pushed extraordinary growth in the biofuel industry that is expected to continue. To date, much of the increase in biofuels has been based on conversion of corn and small grains energy, in the form of starch, to ethanol for use in transportation. Anticipated growth in biofuels production is likely to continue to have important implications for agricultural markets and production practices. Changes in biofuel feedstock sources and production are likely as technologies develop to provide alternatives to the starch based liquid fuels that currently dominate the biofuels industry. Continued growth in biofuels production in the U.S. and globally has significant implications for global livestock production. Challenges have been identified for livestock feeding operations with an increase in biofuels production because readily available feed energy for livestock production is also ideal as a biofuel feedstock energy source. This ‘new energy crisis’ coupled with the anticipated growth of the world population to 9 billion by 2050 and the growing demand for animal source foods has sparked a need for greater innovation in livestock production practices. Corn and other grains are the primary energy form used to support animal production, particularly swine and poultry. Ruminants have reduced reliance for energy derived from starch-containing feeds because they can derive energy from the digestion of cellulose and other plant fibers as a consequence of the presence of fiber digesting bacteria in the rumen. This evolutionary advantage of ruminants that permits the capture of energy for meat and milk from the fermentation of fiber in the rumen has partially insulated beef and dairy production from competition with starch based biofuels production. Diversion of corn to ethanol and the resulting co-products of corn biofuels have decreased the availability of starch for many livestock but have increased the availability of corn protein primarily in the form of distiller's grain and solubles (DDGS). Several excellent reviews have highlighted the milling process alternatives in ethanol production and the feeding value of resulting co-products including DDGS (Klopfenstein et al., 2008; Berger and Singh, 2009; Schingoethe et al., 2009) and serve to underscore the possibilities and potential problems with DDGS feeding. The current review focuses on the potential competition for other sources of plant energy, primarily cellulose, and the interplay with feed resources in ruminant livestock production and cellulosic ethanol production. Efficient cellulosic-based liquid fuel production is constrained by many of the same issues that have limited efficiency of (fiber-based) ruminant livestock production, namely the release of cellulose from plant material and further breakdown of component sugars for bacterial fermentation in the rumen. The inability of rumen bacteria to release adequate levels of energy from many crop residues has limited their value and utility for livestock production. A developed and operating infrastructure for supplying large volumes of crop residue to centralized processing facilities and efficient release of cellulose and component sugars from plant feedstocks are currently limitations for development of cellulosic ethanol. Significant potential exists for the biofuels industry to utilize corn stover and cereal grain straws as cellulosic biofuels feedstocks. Technologies are sought, and being developed, that enable efficient release of fermentable sugars from these residues. Harmonizing the goals for cellulosic biofuels and ruminant livestock production holds exciting possibilities for both industries. Lateral transfer of technologies to ruminant livestock production that would significantly enhance capture of energy from crop residues represents an unprecedented opportunity for enhanced productivity from existing agricultural systems, especially where crop residues are underutilized. Successful development of these technologies will have a global impact in areas where crop quality and quantity is marginal and plant fiber digestibility by ruminants currently constrains productivity and compromises food security. Alternatively, cellulosic biofuels production has the potential to divert a portion of the current and future forage production toward cellulosic biofuels production and highlights the challenges associated with meeting global demands for both food and energy when water and land availability may be limited. Role of Growing Population and Demands for Animal Source Foods World population is expected to reach 9 billion by 2050 and represents an increase of 34% and a rise in urban dwellers to 70% (from 49% currently). Estimates indicate limited arable land reserves. Arable land as hectares per person has declined from 0.38 to 0.21 from 1960 to 2010 (http://www.worldbank.org). Consequently, the need for efficient food production is greater now than at any other time in history. The urgency for improved efficiency has sparked innovation in the livestock production sector. A concomitant increase in world needs for energy, water, and other resources has elevated societal awareness of the interconnectedness of food and biofuels production systems and the necessity for whole systems-based solutions to food and fuel production. This need is intensified in a background of global climate change and potential impacts on agricultural systems. The demand for animal source foods has increased steadily over the past 50 years and is projected to continue to increase, albeit at a diminishing rate compared with the previous century. Worldwide, animal source foods will play an increasingly important role in calorie (Figure 1) and protein supply, with much of the growth in developing countries. This increased demand is driven by a combination of an increase in population, increased average worldwide stature resulting in an increased daily energy requirement, and a shift toward increased protein quality linked to economic growth and improved individual income security (Irz et al., 2003). Consequently, it is incumbent on animal scientists and livestock producers to continue to develop more efficient production systems that are low impact and more integrated with overall food production and the environment. Figure 1. View largeDownload slide Global per capita energy consumption and sources of calories (FAO, 2009; Cole, 2000). Figure 1. View largeDownload slide Global per capita energy consumption and sources of calories (FAO, 2009; Cole, 2000). Crop Residues and Fuel Production Potential The most important crops used for food, feed, and fiber on a worldwide basis are wheat, rice, corn, soybean, sugarcane, and cotton. Only one-half of the energy captured by grain crops is stored in the harvestable grain. Therefore, the energy potential from crop residues is significant. There is approximately 1868 tg of crop residue worldwide from production of primary food and feed grain crops (Kim et al., 2009). Rice is the greatest source of crop residue at 731 millions of tons, followed by corn at 520 millions of tons (Figure 2). Corn residue contributes the bulk of crop residues in North America and approximately 196 million megagrams of stover per year is attributable to U.S. production (Graham et al., 2007). There is approximately 34 million megagrams of residues from other crops in the U.S. including wheat, barley, oats, rice, rye, and sorghum. The bulk of harvestable corn stover is found in the upper mid-west United States and quantities that can be sustainably harvested are determined by cropping and tillage practices (Graham et al., 2007). Agronomically sustainable practices may enable 30 to 60% of the available stover to be removed without affecting future productivity of cropped acres (Wilhelm et al., 2007). The U.S. Department of Energy estimates that 30% of petroleum consumption can be replaced by approximately 900 million megagrams of biomass and that corn stover could meet 20% of the total biomass required to achieve this goal (Graham et al., 2007), which would supply 6 to 10% of current annual liquid fuel needs. Figure 2. View largeDownload slide Estimated worldwide mass (in millions of tons) of residue from primary crops (Kim et al., 2009). Figure 2. View largeDownload slide Estimated worldwide mass (in millions of tons) of residue from primary crops (Kim et al., 2009). Ethanol from plant feedstock Most of the ethanol produced from corn grain is the result of dry milling. In this process, the grain is screened and ground into coarse flour, commonly referred to as “meal.” A slurry is formed by the addition of water to form a “mash” and simple sugars are released from the starch by the addition of enzymes. The pH of the mash is stabilized to approximately 5.8. Free sugars released by enzymatic hydrolysis are fermented to ethanol and the remaining components including proteins, fiber, minerals, and fat are recovered in the co-products, distillers grains, and distillers solubles. The corn fiber found in the corn grain contains cellulose and hemicellulose which are not fermented in this process, and therefore these fibrous materials are contained in DDGS. Every 25 kg of corn processed for ethanol yields approximately 10.6 L of ethanol and 6.8 kg DDGS of which 2.2 kg is corn fiber. Separation of corn fiber is possible using floatation (Singh et al., 1999) or by sieving and air flow (elutriation) at grinding (Srinivasan et al., 2005). Alternatively, corn fiber may be hydrolyzed to constituent sugars by the addition of cellulose degrading enzymes that release primarily glucose, xylase, and arabinose. Cellulase digestion of corn fiber and subsequent fermentation may enable a 1.2 to 2.7% increase in ethanol yield from dry mill ethanol production (Srinivasan et al., 2005). Consequently, there is interest in developing this technology for use with corn and other fiber sources. Widespread adoption of this process for cellulosic ethanol production is hampered by the cost of fibrolytic enzymes and the rate of sugar release from cellulose (i.e., digestion rate) and the efficiency of cellulose breakdown (i.e., extent of digestion). The release of sugars from cellulose is also the limiting step in the use of crop residues such as corn stover for ethanol production. Interestingly, the same processes of fiber degradation, cellulose digestion and saccharification limit the nutritive value of many forages and crop residues for ruminant livestock production. Plant residues to cellulosic ethanol Conversion of lignocellulose to ethanol requires pretreatment to disrupt the lignin, cellulose, and hemicellulose structure, followed by hydrolysis of sugar polymers to yield free sugars, then fermentation to ethanol and separation and purification of the products as described in detail by Lee and Lavoie (2013). Pretreatment is a necessary first step in deriving fermentable sugars from plant material that contains lignin, cellulose, and hemicellulose. The release of cellulose and hemicellulose is limited by the nature of lignin crosslinking. Disruption of this crosslinking makes cellulose and hemicellulose more accessible and enhances the rate and efficiency of glucose, xylose, and arabinose release during enzymatic saccharification. Pretreatment is viewed as one of the most expensive and limiting steps in the conversion of cellulose biomass to ethanol (Mosier et al., 2005). Effective pretreatment has the ability to lower the barriers to using lignocellulose biomass for ethanol production. Consequently, there is considerable interest improving the cost and efficiency of this process. Any effective pretreatment strategy should 1) release as much fermentable sugar as possible in a short time, 2) require low enzyme loading, 3) involve minimal handling of plant material, 4) be scalable to handle high biomass quantities, 5) require minimal water consumption, and 6) not inhibit downstream enzymatic digestion or fermentation (Mosier et al., 2005). The necessity for efficient downstream enzymatic digestion and fermentation for lignocellulosic ethanol production are highly compatible with the pretreatment of crop residues for ruminant livestock production. View largeDownload slide Corn stover residue (photo credit: Idaho National Laboratory Bioenergy Program). View largeDownload slide Corn stover residue (photo credit: Idaho National Laboratory Bioenergy Program). Biomass pretreatment strategies The most common pretreatment processes used for lignocellulose ethanol production are 1) mechanical size reduction such as chopping or extrusion, 2) chemical hydrolysis through the action of alkali such as sodium or calcium hydroxide or treatment with dilute acids, ammoniation, or peroxides, 3) heat and hydration including steam, and 4) enzymatic hydrolysis. Regardless of the pretreatment strategy employed, the end product is a plant biomass that contains more free sugar or permits more access to enzymes. There is considerable overlap in the pretreatment strategies being examined for cellulosic ethanol and strategies to enhance the availability of nutrients in crop residues for ruminant livestock. There is one notable difference, however, in that pretreatment schemes for cellulosic ethanol are being developed for scaling to centralized facilities, whereas pretreatment of crop residues for livestock feed tends to be scaled to point of use (i.e., closer to the field and to livestock facilities). A depot model for pretreatment may enable more aggressive treatment schemes, thus enabling greater sugar yield or physical fractionation of streams to provide for a greater overall yield of fermentable sugars and production of specialized biobased products. Conversely, a model that involves pretreatment on farms where stover is produced on small local centers (i.e., a distributed model of pretreatment), may produce a less uniform product, but may provide lower cost and more flexibility in using treated end products for either the biofuels industry or for livestock feeds. View largeDownload slide The reliance of ruminants on starch-containing feeds for energy is reduced because of a fiber-digesting bacteria in the rumen that allows them to derive energy from digesting cellulose and other plant fibers (photo credit: Jeff Frisbee). View largeDownload slide The reliance of ruminants on starch-containing feeds for energy is reduced because of a fiber-digesting bacteria in the rumen that allows them to derive energy from digesting cellulose and other plant fibers (photo credit: Jeff Frisbee). Deconstructing fibrous material by grinding, chopping, or shredding followed by chemical pretreatment is the most common scheme to enhance the availability of cellulose in plant biomass, whether the intended use is for industrial conversion or livestock feed. Pretreatment causes the lignocellulosic biomass to swell, resulting in an increase in internal surface area. The crystallinity of lignin is reduced and the disruption in lignin structure leads to greater solubility of cellulose and hemicellulose which in the presence of cellulose degrading enzymes increases the yield of fermentable sugars. The pretreatment of plant biomass and subsequent enzymatic digestion of cellulose yield glucose, whereas the digestion of hemicellulose yields primarily glucose and xylose and a mixture of arabinose, galactose, fucose, mannose, and glucuronic acid. Corn stover contains approximately 37.5% glucose, 22.4% xylan, and 17.6% lignin by weight, and assessment of pretreatment strategies are determined by the yield of glucose and xylose per kg of stover (Mosier et al., 2005; Wyman et al., 2005). Pretreatments that have cost-effective potential include physical pretreatments, such as steam explosion and liquid hot water (LHW), that are performed at temperatures of 180 to 230°C and high pressures, whereas effective chemical pretreatments include ammonia, dilute sulfuric acid, sodium hydroxide, and calcium hydroxide (lime). Pretreatment with acid and alkali is compatible with pretreatment strategies of crop residues for both biofuels use (Digman et al., 2010) and as feed for ruminant livestock production. Pretreatment with alkali, particularly lime (calcium oxide), is a cost effective pretreatment strategy that yields high levels of glucose and xylose from corn stover when subsequently subjected to enzymatic hydrolysis (Mosier et al., 2005). Furthermore, lime pretreatment is an effective on-farm pretreatment for wet biomass such as switchgrass (Digman et al., 2010) and has been considered as a component of a distributed model for biomass pretreatment. Pretreatment with lime and other alkali has been evaluated for several decades as a means to enhance the nutritive value of corn stover and straw for sheep, beef, and dairy cattle (Klopfenstein and Owen, 1981). Likewise, ammoniation has been explored as as method for improving feeding value of low quality forages (Patterson et al., 1981). Development of bioenergy coupled with increased demand for food animal production has precipitated a resurgence of interest in alkali pretreatments as part of a refined strategy to use low quality crop residues for livestock production. Because of the overlap in attributes for the end products of pretreatment strategies for biofuels production and use of crop residues in livestock, there are exciting new possibilities for technology development that will likely benefit both sectors. Improving the Feeding Value of Crop Residues Nutritional value of plants for cattle is determined by the amount the animal will voluntarily consume, the breakdown of the feed in the digestive tract, and the utilization efficiency of the digestion end products. Digestion of fiber by rumen bacteria yields energy for bacterial growth and, in the anaerobic environment of the rumen, results in the formation of short chain fatty acids, primarily acetate, propionate, and butyrate. These volatile fatty acids are absorbed through the rumen wall into blood and serve as the primary energy source for ruminants. Yield of energy per unit of time in the rumen is determined by the chemical and physical composition of feeds. For forage crops and plant residues, this is primarily dependent on the content and organization of plant carbohydrates. The most prevalent forms of carbohydrates in forages and crop residues are cellulose and hemicellulose. These polymers of glucose and pentoses are organized in a complex of three-dimensional structural carbohydrates in plant cell walls. The crystallinity of cellulose and hemicellulose polymers and the degree of physical and chemical association with lignin is a function of location within the plant (i.e., stem nodes and internodes) and stage of plant maturity. These factors ultimately determine the accessibility of bacteria to cellulose and hemicellulose and digestibility in the rumen when the plant is consumed by ruminants. Chemical pretreatment of crop residues result in physical redistribution of lignin and hemicellulose within the plant material, and changes in cellulose crystallinity (Banerjee et al., 2012) result in increased hemicellulose solubility and an increased rate of cellulose and hemicellulose digestion by rumen microbes (Klopfenstein and Owen, 1981). The resulting combination of increased rate and extent of digestion of cellulose and hemicellulose in the rumen enhances the energy value of the crop residue. Early studies indicated that pretreatment of corn stover with a combination of 2% sodium hydroxide and 2% calcium oxide resulted in a 53% increase in feed intake in growing lambs and a 12% increase in dry matter digestibility (Oji et al., 1977). Innovation in forage harvesting and processing equipment have improved corn fiber digestion through crushing and shearing of stover and cobs (Johnson et al., 1999) and may further enhance the effect of pretreatment of stover with alkali on digestibility. Recent studies indicate a 6 to 9% increase in total tract dry matter digestibility in lambs fed corn fiber pretreated with a combination of alkali and heat. Similar feedlot performance was achieved when high moisture and dry rolled corn was replaced by calcium oxide treated corn stover to a level of 20% of the ration (Shreck et al., 2012). Although sodium hydroxide is effective in improving the digestibility of several crop residues, it is expensive, corrosive, poses human health risks in handling, and the resulting feeds may provide excess dietary sodium relative to animal requirements. Calcium oxide (CaO) powder, also known as quicklime, is one of the more cost effective sources of alkali (Kaar and Holtzapple, 2000). When combined with water, CaO is hydrated to Ca(OH)2, which is an exothermic reaction resulting in heat generation. Effectiveness of pretreatment of corn stover with calcium oxide are: pretreatment time, temperature, calcium hydroxide loading, water loading, and biomass particle size. Treatment of stover with 7% CaO and addition of water to 50% DM resulted in nine times greater release of glucose and xylose after incubation with cellulase (Kaar and Holtzapple, 2000). Short term studies indicate that corn stover when treated with 5% CaO and added water to 50% dry matter can replace corn silage in diets for lactating dairy cows to at least 25% of the total ration (Donkin et al., 2012). Direct Use of Novel Biofuels Co-products Energy Sources as Feeds Biodiesel glycerol is an attractive source of energy for dairy and beef cattle. Every ton of biodiesel that is produced generates about 100 kg of crude glycerol. According to the National Biodiesel Board, the production of biodiesel in the U.S. over the next decade is expected to grow. The use of glycerol in the treatment of ketosis in dairy cows was reported as early as 1954. Several studies indicate a potential value of glycerol in treating ketosis but feeding rates for most studies are limited to 5 to 8% of the diet DM. Studies in the author's laboratory have demonstrated equivalent productivity when corn grain is replaced by glycerol as a macro-ingredient in rations for transition and lactating dairy cows. While glycerol is a promising replacement for corn grain in rations for dairy (Donkin et al., 2009, Carvalho et al., 2011) and beef cattle (Ramos and Kerley, 2012), competition exists to ferment glycerol to biofuel ethanol. Newly isolated bacteria appear to be able to ferment biodiesel-derived crude glycerol to ethanol with high yield and productivity (Choi et al., 2011). The cost of glycerol coupled with reduced operating costs result in ethanol production from glycerol that is 56% cheaper than ethanol production from corn (Yazdani and Gonzalez, 2007). Consequently, the availability of glycerol as a replacement for corn may be limited as glycerol fermentation to ethanol is commercialized. These relationships serve to highlight the connectedness of feed energy demands for livestock production and energy demands for liquid fuels. New Technologies to Release Plant Energy Lignin polymers are the result of the coupling of p-hydroxycinnamyl alcohol monomers. This family of compounds is mainly located in plant cell walls and covalently bound to hemicelluloses to provide thickening and rigidity to the plant cell wall, form the plant vascular system, and enable plants to grow vertically. The structure and association of lignin polymers is significant because it is the dominating negative factor for both forage digestibility in livestock production and lignocellulosic biofuels production. Significant progress has been achieved over the past two decades in understanding the structure and functional properties and biosynthesis of lignin. This knowledge has expanded possibilities for manipulating lignin biosynthesis to enhance attributes for biofuels and ruminant livestock alike. Figure 3. View largeDownload slide Strategies to increase yield of cellulosic ethanol and synergy with use of low-quality crop residues for ruminant livestock. Traditional corn stover is pretreated to alter lignin (red rectangles) structure and increase the accessibility of cellulase and other enzymes to cellulose (green rectangles), which results in the release of free sugar (light green pentagons). Likewise, brown midrib corn stover or low lignin transgenic corn stover is subjected to pretreatment to yield more free sugar due to greater accessibility to cellulose. Treatment with ligninase increases yield of sugars by reducing lignin content and increasing accessibility to cellulose by microbes. Technologies used to enhance the efficiency of cellulosic ethanol production are likely to be compatible with increased milk and meat production from crop residues with inherently low digestibility. Figure 3. View largeDownload slide Strategies to increase yield of cellulosic ethanol and synergy with use of low-quality crop residues for ruminant livestock. Traditional corn stover is pretreated to alter lignin (red rectangles) structure and increase the accessibility of cellulase and other enzymes to cellulose (green rectangles), which results in the release of free sugar (light green pentagons). Likewise, brown midrib corn stover or low lignin transgenic corn stover is subjected to pretreatment to yield more free sugar due to greater accessibility to cellulose. Treatment with ligninase increases yield of sugars by reducing lignin content and increasing accessibility to cellulose by microbes. Technologies used to enhance the efficiency of cellulosic ethanol production are likely to be compatible with increased milk and meat production from crop residues with inherently low digestibility. The classical pathways of lignin biosynthesis depicts polymers that vary in content of the three dominant monolignols in plants: p-coumaryl, coniferyl, and sinapyl alcohol, which yield H, G, and S lignin respectively (Vanholme et al., 2008). It is now clear that intermediates of lignin synthesis and individual classes of lignin polymers can incorporate into lignin at different levels to impact plant growth properties and biomass digestibility. One of the most striking examples of manipulation of this pathway is the classic research of Chen and Dixon (2007). Using antisense RNA technology, these researchers systematically knocked out each of the six critical reactions in lignin biosynthesis to generate six different alfalfa plants. Some of the resulting lignin modified plants had glucose release rates in the presence of cellulase that were similar to lignin free plant material which indicates the lignin present did not impair digestion. Novel manipulation of lignin may lead to production of plants that are more efficiently converted to biofuels. The attributes of brown midrib corn and sorghum with reduced lignin concentration and improved cell wall digestibility have been recognized for some time (Cherney et al., 1991). A greater understanding of lignin biosynthesis and impacts of manipulating these pathways for efficient biofuels production will have dual application for ruminant livestock production. Ruminants have evolved highly efficient processes for digesting plant cell wall materials as a consequence of the symbiotic microbiome that inhabits the rumen. This microbiome contains a consortium of microbes that contain a complex system for attachment to and digestion of lignocellulosic plant biomass. In a very similar manner, the ability of termites to digest lignocellulose is a function of the microbial symbionts located in the third proctodeal segment, or hindgut paunch, of the termite (Warnecke et al., 2007). Microbial fermentation of lignocellulosic plant biomass in both cases generates acetate, methane, carbon dioxide, and microbial protein. Similar to ruminants, the primary source of energy for termites is acetate derived from bacterial fermentation of plant biomass. Until recently, it was thought that termite digestion of lignocellulose was solely the result of unique enzymes produced by the microbial symbionts located in the hindgut paunch. However, there is mounting evidence that the host-derived activities encoded in the termite genome are also responsible for this digestion (Scharf et al., 2011). Furthermore there is growing evidence indicating host (termite) produced lignases and phenol-oxidases that breakdown lignin to release cellulose (Coy et al., 2010; Scharf and Boucias, 2010). It appears that for the termite, there is a host and symbiont synergism that maximizes the release of fermentable monosaccharide glucose from lignocellulose. The origin of the host enzymes appears to be from salivary glands or other parts of the upper digestive tract of the termite. When isolated using recombinant DNA technology and propagated using insect biotechnology, the lignin digesting properties of the enzyme are observed in the laboratory (Scharf et al., 2011). Scalable application of these discoveries provides a strategy to enhance lignocellulosic degradation that may revolutionize ethanol production and simultaneously enhance opportunities to use crop residues for livestock feed. View largeDownload slide Like ruminants, termites are able to digest lignocellulose thanks to microbial symbionts within the insect (photo credit: Gnilenkov Aleksey). View largeDownload slide Like ruminants, termites are able to digest lignocellulose thanks to microbial symbionts within the insect (photo credit: Gnilenkov Aleksey). Conclusion World demands for food and energy in the coming decades will accelerate the necessity for innovation to overcome limitations to more efficient livestock production. Biological innovations that unlock the potential for lignocellulosic and other biofuels are likely to have direct applications to ruminant livestock production. The quest to overcome limits for efficient ruminant livestock production has significant overlap with biofuels production. Several promising technologies are emerging and there is extensive ongoing research that will provide options and opportunities for synergies between ruminant livestock production and biofuels that will enhance the capacity to feed and fuel the planet. Dr. Shawn S. Donkin has been a faculty member of Purdue University since 1995. He was promoted to professor of animal sciences in 2006. Donkin has developed an internationally recognized research program in the area of dairy cattle nutrition and health. Ongoing fundamental studies in his laboratory explore the role of nutrition, physiological changes, and environmental stressors on genes critical to health and productivity. Applied nutrition studies in his laboratory evaluate alternative energy and protein feeds for transition and lactating cows. He received an associate degree in agriculture from The Nova Scotia Agricultural College in 1980, a B.Sc. degree from McGill University (Montreal) in 1982, and worked in the feed industry and as a dairy herd manager before returning to university to pursue graduate education. He earned an M.S. degree in dairy and animal science from Pennsylvania State University in 1987 and a Ph.D. in dairy science from the University of Wisconsin–Madison in 1992. Dr. Perry Doane is a research scientist for Archer Daniels Midland Company working in animal nutrition. As part of the feed research group, Doane is involved with research and development of ruminant feed ingredients. His efforts in fiber nutrition have involved pre-processing and handling of agricultural residues and use of biofuel co-products. He received his Ph.D. from Cornell University in 1997, joined ADM Alliance Nutrition as manager of dairy research, and transferred to the ADM Research Division in 2008. 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Google Scholar CrossRef Search ADS PubMed  Footnotes 1 Material in this article was presented at the CSAS symposium held at the 2012 ADSA-AMPA-ASAS-CSAS-WSAS Joint Annual Meeting, held in Phoenix, AZ (USA), July 15–19, 2012. © 2013 Donkin, Doane, and Cecava This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com
TI - Expanding the role of crop residues and biofuel co-products as ruminant feedstuffs
JF - Animal Frontiers
DO - 10.2527/af.2013-0015
DA - 2013-04-01
UR - https://www.deepdyve.com/lp/oxford-university-press/expanding-the-role-of-crop-residues-and-biofuel-co-products-as-1c0Fo3uaWu
SP - 54
EP - 60
VL - 3
IS - 2
DP - DeepDyve
ER -