Corn gluten feed is the by-product of the wet-milling of maize grain for starch (or ethanol) production (Hoffman et al., 2010). Corn gluten feed consists mainly of maize bran and maize steep liquor (liquid separated after steeping) but may also contain distillers solubles, germ meal, cracked maize screenings, as well as minor quantities of end-products from other microbial fermentations (Stock et al., 1999). The chemical composition of corn gluten feed varies hugely, as it depends on the milling process and on the relative proportions of bran, steep liquor and other components. Particularly, the energy and protein content of corn gluten feed are positively correlated to the proportion of steep liquor in the blend (Stock et al., 1999).
The wet-milling process of maize is described in the figure above. The process yields 5 main products: maize starch, maize germ oil meal, corn gluten meal, corn gluten feed and maize steep liquor. After cleaning and removal of foreign material, the maize grain is usually steeped in water with sulfur dioxide (SO2) for 24-40 hours at a temperature of 48-52°C. The role of sulfur dioxide is to weaken the glutelin matrix by breaking inter- and intramolecular disulfide bonds. Steeping at 45-55°C favours the development of lactic acid bacteria that produce lactic acid, lowering the pH of the medium and thereby restricting growth of most other organisms. At the end of steeping phase, the maize kernels contain about about 45% water, have released about 6.0-6.5% of their dry substance as solubles into the steepwater and have become sufficiently soft to be pulled apart easily with the fingers (BeMiller et al., 2009). After steeping, the maize kernels are coarsely ground so that the germs are separated from the endosperm and used for oil extraction which yields maize germ oil meal. The remaining steeping water is condensed into a steep liquor. The endosperm undergoes further screenings that separate the fibre from gluten (protein fraction) and starch slurry. Fibre (bran) can be mixed with steep liquor and maize germ oil meal to create corn gluten feed (ISI, 2008; RFA, 2011). The fibre-free endosperm is centrifugated in order to separate the starch fraction and the gluten, which have different densities, resulting in almost pure starch (99% starch), and corn gluten meal (CRA, 2006).
Corn gluten feed is a feed ingredient mostly used in cattle diets as a source of energy and protein. Its economic value depends upon the relative price of whole grain and protein feeds. In the United States, it is usually considered as a source of protein (Ash, 1992). However, in the late 1980s, corn gluten feed was one of the several duty-free Non Grain Feed Ingredients that the European feed industry imported massively from the USA as a source of energy, to substitute for EU cereal grains that were very expensive at the time. Corn gluten feed imports declined after the Common Agricultural Policy (CAP) reforms reduced EU grain prices (Ash, 1992; Hasha, 2002).
Corn gluten feed is usually sold after drying, but maize processors may save on drying cost by selling wet corn gluten feed.
Note: it is important to note that corn gluten feed should not be mistaken for corn gluten meal, which contains about 65% crude protein instead of 22% and is nutritionally completely different. The name similarity of these products is an occasional source of confusion, particularly in papers written by non-native English speakers.
Dried corn gluten feed is traded worldwide. Corn gluten meal and corn gluten feed production is relatively constant since ethanol is now mainly produced in dry mills (RFA, 2008). The consumption of corn gluten meal and corn gluten feed together was about 14.9 million t from October 2010 to September 2011. The main consumers of both products are the USA (5.6 million t), EU (3 million t), South Korea (1 million t), Japan (0.94 million t) and other Asian countries (1.6 million t). The USA supply 60% (2.1 of 3.5 million tons) of the corn gluten feed traded worldwide. The main importers for 2010-2011 were the EU, South Korea, Turkey, China, Japan, Israel, Egypt and Indonesia (Oil World, 2011).
Unlike dried corn gluten feed, wet corn gluten feed spoils easily and is usually distributed nearby maize processing plants.
Wet corn gluten feed spoils very quickly and must either be fed within 6-10 days or stored in anaerobic conditions in a sealed structure (Iowa RFA, 2011). Good results have been obtained by mixing it with other feedstuffs such as maize grain, maize silage or haylage. Packing the material into silo bags is an excellent means for maintaining its quality. The material undergoes little apparent fermentation because of the relatively low pH (4.3). Wet corn gluten feed stored in a silage bag for one year maintained its composition. In cold climates, freezing temperatures actually extend the storage life of wet corn gluten feed and it was even possible to store unprotected wet corn gluten feed on the ground in winter (North Dakota) with little spoilage for up to three to four weeks. However, high summer temperatures reduce freshness to only three to four days, causing palatability problems (Schroeder, 2010).
Corn gluten feed is a major feed ingredient in ruminant diets, particularly for beef and dairy cattle. Wet corn gluten feed contains 40 to 60% DM (Stock et al., 1999) while the dry product contains about 88% DM. Corn gluten feed is a moderately high source of protein: it contains about 20-25% DM of protein, more than cereal grains and milling by-products but less than corn gluten meal, distillers' grains and most oil meals. Corn gluten feed is much richer in cell wall constituents than maize grain (crude fibre 6-10% DM, NDF 31-49% DM, ADF 8-13% DM and a low lignin content about 1.2% DM) which tends to limit its use in pig and poultry diets. The crude fat content is usually under 4% DM. Corn gluten feed contains relatively high and quite variable amounts of residual starch, from 11% to more than 30% DM. Ash content is also important (about 7% DM).
The composition of corn gluten feed is influenced by the proportion of steep liquor, which contains more energy and protein than the bran (Scott et al., 1997). The ratio of steep liquor to bran is generally 1:3 to 2:3 and differences in nutritive value between products containing low or high levels of steep liquor can be important (Schroeder, 2010; Stock et al., 1999). Corn gluten feed varies in color from yellow-light brown to dark brown, depending on the amount of steep liquor, drying temperature and drying time. Dried corn gluten feed generally darkens with increased drying temperature or time. Extremely dark corn gluten feed with a "burned" smell may be heat damaged and the protein digestibility may be reduced (Schroeder, 2010; Myer et al., 2011).
Corn gluten feed is low in calcium but has relatively high levels of phosphorus and potassium (Maiga et al., 1997). The problem of excess sulfur for cattle has been described in Potential constraints.
Sulfur dioxide is added during the wet milling process to aid in the extraction of starch. As a result, the sulfur concentration in corn gluten feed ranges between of 0.33 to 0.73% DM, which may be higher than the upper safe limit in cattle. Feeding large amounts of corn gluten feed can lead to sulfur toxicity, leading to reduced feed intake and possibly death. A specific disorder associated with excess sulfur is polioencephalomalacia ('brainers') which affects the nervous system, causing blindness, incoordination, and seizures. Excess dietary sulfur can also increase the risk of a copper deficiency (Myer et al., 2011).
Corn gluten feed is a relatively high fibre, medium-energy, medium-protein product that is essentially fed to ruminants. Its fibre is highly digestible by ruminants and corn gluten feed can be substituted for grains, such as maize grain, to reduce the starch load in the rumen (Rausch et al., 2006). The high fibre content may help to prevent rumen acidosis. Corn gluten feed is low in lysine, and amino acid supplementation could be considered if dietary lysine concentration is a concern (Myer et al., 2011).
In vivo OM digestibility values found in the literature for dried corn gluten feed vary from 70 to more than 80%. Differences in composition (steep to bran ratio, starch and fibre content) as well as processing conditions (drying temperature and drying time) may explain this variability. Corn gluten feed has slightly lower OM digestibility in sheep than in cattle (72% vs. 75%) (O'Mara et al., 1999). Published ME values vary from 11.4 to 12.2 MJ/kg DM (NRC, 2001; Sauvant et al., 2004) while NE for lactation values range from 6.9 (NRC, 2001 at 3 x maintenance) to 7.4-7.5 MJ/kg DM (Fonnesbeck et al., 1984; Gunderson et al., 1988; Sauvant et al., 2004 and NRC, 2001 at 4 x maintenance).
Drying corn gluten feed reduces its energy. For instance, wet corn gluten feed contained more NE for gain (estimated from animal performance) than dried corn gluten feed when fed to finishing cattle (Ham et al., 1995). This could be partially explained by the loss of volatile compounds in the steep fraction during extensive drying (over 60°C) (Stock et al., 1999). Also, fibre in wet corn gluten feed is somewhat more digestible than in the dry form, permitting greater intakes of wet vs. dry corn gluten feed (Schroeder, 2010). In beef cattle, wet corn gluten feed contained more NE (estimated from animal performance) than dry-rolled maize grain when fed to growing diets (Stock et al., 1999) and 90 to 100% of the NE of maize grain in finishing diets (Firkins et al., 1985; Ham et al., 1995; Schrage et al., 1991).
Rumen escape protein in corn gluten feed is about 24-30% (Mertens, 1977; Firkins et al., 1985; Bernard et al., 1988; NRC, 2001; Sauvant et al., 2004). Values for wet gluten feed are in the lower range (25%; Schroeder, 2010). As a consequence, the inclusion of corn gluten feed should be minimized in diets that contain dietary ingredients with high soluble protein concentrations, such as silages.
Absorbable phosphorus content in corn gluten feed is about twice that in maize grain (Sauvant et al., 2004). It tends to exceed P requirements in cattle, which may lead to the formation of urinary calculi and to P accumulation in urine and manure (Hankins et al., 2005; Myer et al., 2011).
Corn gluten feed has a bitter taste that affects palatability and results in lower intake until animals adapt to it (Rausch et al., 2006). For instance, steers fed a diet containing 40% wet corn gluten feed spent less time at the feeding bunk than animals fed the control diet (Parsons et al., 2007). Corn gluten feed has a low mean particle size (less that 10% of its dry matter is retained by a 1 mm screen aperture), which is not favourable to chewing. Rumination time, chewing activities and rumen pH were negatively affected when 18% and 25% dry corn gluten feed were substituted for corn silage (Biricik et al., 2007). The inclusion of chopped alfalfa hay to dairy cows diets rich in wet corn gluten feed increased consistency of the rumen mat and rumination activity resulting in greater rumen digestion of NDF (Allen et al., 2000).
Numerous trials in North America have investigated the effects on dairy performance of replacing forages or concentrates with dry and wet corn gluten feed. Generally, it was found that high levels of wet corn gluten feed could be included in the diet of dairy cows. Cows fed 20 to 35% (DM basis) wet corn gluten feed produced energy-corrected milk more efficiently than controls. Milk protein and lactose yields increased when corn gluten feed was fed and, while milk fat percentage was lower, fat yield remained unaffected (VanBaale et al., 2001). Another trial found that diets may be formulated to contain as much as 37.5% wet corn gluten feed (DM basis) and the increase in total milk yield compensated the reductions in milk fat concentration, thereby maintaining total milk fat yield (Kononoff et al., 2006). Dry matter intake, milk yield and milk composition were not significantly affected by replacing concentrate with wet maize gluten feed at up to 34% of DM intake (Armentano et al., 1986). Dried corn gluten feed could support milk production levels equal to diets based on maize grain and soybean meal when fed to dairy cows in mid-lactation at 22% of DMI (Bernard et al., 1991). In Brazil, the inclusion of 16% of dried corn gluten feed was found economically profitable (Alves et al., 2007).
Not all studies have been entirely favourable. A linear decline in DM intake and milk yield was observed with maize silage-based diets containing from 0 to 40% (diet DM) wet corn gluten feed (Staples et al., 1984). A similar decrease in milk yield was noted when 30% of wet corn gluten feed or more was included in the diet (Schroeder, 2003). It has been suggested that the optimal inclusion level for corn gluten feed depends upon the feedstuffs being substituted for, as well as on the other ingredients contained in the ration (Boddugari et al., 2001). An optimally formulated wet corn gluten feed product could replace up to 100% of the concentrate and at least 45% of the forage in diets for lactating dairy cows containing 54% forage, which would translate into nearly 70% of the total ration DM (Boddugari et al., 2001).
A considerable amount of research has been dedicated to investigate the use of corn gluten feed in North American feedlot diets.
Relatively high levels of wet gluten feed can be included in feedlot diets, with often positive (but variable) effects on performance. This positive response is likely to be due to reduced rumen acidosis, increased DM intake, and also to a reduction in negative associative effects of rumen fermentable starch on fibre digestion (Boddugari et al., 2001). However, due to potential sulfur toxicity, corn gluten feed should be limited to 50% or less of the total DM intake (Myer et al., 2011).
Wet corn gluten feed replacing various levels of dry-rolled maize grain had a positive effect on average daily gain (up to 15% higher) and on feed efficiency (up to 5% higher) (Stock et al., 1999). Feed efficiency was generally improved by the addition of wet corn gluten feed to dry-rolled maize finishing diets (Richards et al., 1998). Wet corn gluten feed could substitute up to 25 or 50% of dietary DM without negative effects on feedlot performance, digestibility of nutrients, or carcass characteristics (Hussein et al., 1995). 40% (diet DM) wet corn gluten feed replacing steam-flaked maize increased DM intake and daily gain but decreased feed efficiency (Parsons et al., 2007). The same amount of wet gluten feed increased digestibility of organic matter and NDF (Montgomery et al., 2004). Wet corn gluten feed could be used at up to 35% (diet DM) without adversely affecting performance (Macken et al., 2004). Wet corn gluten feed (25 to 35% diet DM) could be used as a source of energy in finishing diets based on steam-flaked corn and, as a source of fibre, partially fulfilling roughage requirements (Sindt et al., 2003).
In restricted diets the value of wet corn gluten feed relative to steam-flaked maize might be increased with increased concentrations (30% vs. 10-20% DM) of alfalfa hay (Montgomery et al., 2003). Restricting feeding during growing may be a strategy that improves the utilization of corn gluten feed at high inclusion rates (Hussein et al., 1995).
Carcass quality can be altered by wet corn gluten feed supply: steers fed fine-rolled grain contained more fat than steers fed 50% wet corn gluten feed (Loe et al., 2006).
Dried corn gluten feed could completely replace finely ground maize in finishing diets without affecting negatively feed efficiency and Net Energy (Pereira et al., 2007). Replacement of barley with dried corn gluten feed increased rumen pH, which could help to prevent excessive post-prandial pH decrease (Dragomir et al., 2008). Substituting dry corn gluten feed for maize grain reduced feed efficiency and gain due to the lower digestible energy content of corn gluten feed (Beauchemin et al., 2005).
Modified corn fibre is a by-product produced by a secondary fermentation of maize bran which would enable maize processors to recover more fully ethanol from maize grain. This product has about the same protein content as corn gluten feed but is considerably richer in fibre (ADF 45% DM). Feeding this product (15% dietary level) to growing heifers resulted in a poor performance, suggesting a limited feeding value because of the high acid detergent insoluble nitrogen content (2.5% DM vs. 0.17% DM in corn gluten feed) and slow protein digestion (Peter et al., 2000).
Different forms of corn gluten feed (wet, dry or ensiled) were included at up to 50% of the diet in high-concentrate lamb diets and compared favourably with diets based on maize-urea or maize-soybean meal (Bowman et al., 1988). In growing ewes, dehydrated corn gluten feed included at 10 or 20% dietary levels in a rice straw/concentrate diet resulted in improved animal performance. Daily gain and feed efficiency increased at the 10% inclusion rate (Saleh et al., 2008).
Supplementing goats fed on cocksfoot hay (Dactylis glomerata) with dehydrated corn gluten feed did not change total DM intake, nutrient digestibility, final weight and average daily gain. Carcass dressing was slightly enhanced compared to goats fed hay only (Moore et al., 2002). Dairy goats fed dehydrated corn gluten feed had a higher milk protein concentration than goats fed on other protein sources such as faba beans, sunflower meal or cottonseeds (Sanz Sampelayo et al., 1999).
Corn gluten feed contains more protein than maize grain but its dietary fibre content is also much higher, resulting in a lower energy value. For growing pigs, the Net Energy of corn gluten feed is about 60% that of maize grain (Noblet et al., 2002). In adult sows, who can better digest dietary fibre, the Net Energy of corn gluten feed is 10% higher than for growing pigs (Noblet et al., 2002; Noblet et al., 2000). Another limitation of corn gluten feed in pig nutrition is its low lysine and tryptophan content, combined to standardized ileal amino acid digestibility values, which are 15% lower than for maize grain because of the higher dietary fibre.
The bulkiness of corn gluten feed is a limiting factor at physiological stages with high dietary energy requirements, notably starter pigs, grower pigs and lactating sows. In addition, corn gluten feed has a medium palatability: the increase in feed intake reported in growing pigs is mainly due to the fact that pigs fed diets including corn gluten feed tend to increase feed consumption in order to maintain energy intake. Up to 20% of corn gluten feed can be used in diets formulated for weaning piglets and for growing pigs (Castaing et al., 1990). In finishing pigs, corn gluten feed can be incorporated at up to 30% with no loss of performance (Yen et al., 1971). In sows, corn gluten feed can be used to dilute energy during gestation in order to reduce hunger and improve welfare (Ramonet et al., 1999), health status (Meunier-Salaün et al., 2001) and reproductive performance (Matte et al., 1994). Corn gluten feed can be fed to gestating sows at high inclusion rates (50-70%) with tryptophan supplementation without affecting reproductive performance (Honeyman et al., 1990).
Corn gluten feed is not a very good ingredient for poultry, as its protein and energy content cannot meet the high requirements of poultry production (Rochell et al., 2011). As a consequence, maximum recommended levels are rather low for broilers (about 10%) but higher for laying hens, who have lower energy requirements. Up to 20-25% of corn gluten feed can be included in balanced diets for laying hens without reducing performance (Castanon et al., 1990, El-Deek et al., 2009). Corn gluten feed may be a good ingredient in induced molt programs for layers (Biggs et al., 2004).
Corn gluten feed is a typical ingredient of rabbit diets in Western Europe, particularly in Spain (de Blas et al., 2010). It is used without any problem, mainly as a protein source (even though it is deficient in sulfur amino acids) and as a source of digestible fibre (Fraga et al., 1995). However, its very low lignin content is a limiting factor for its inclusion (5% lignin is recommended to maintain digestive health; Gidenne et al., 2010)), and a supplementary source of lignin must be provided in the diet. The usual inclusion rate of corn gluten feed in rabbit diets is 2 to 10% (de Blas et al., 1995), and up to 20% in some diets (Nicodemus et al., 2002). In experimental studies, it has been possible to include as much as 50% without problems (Villamide et al., 1989).
Corn gluten feed has been used as fish meal replacer in diets of fry and sub-adult tilapia. For fry, a better feed efficiency was obtained in diets containing 67% of corn gluten meal (28% total dietary protein) than in diets containing 30% of gluten feed (32% dietary protein) (Wu et al., 1997; Wu et al., 1996). In sub-adult diets, inclusion can range between 13 and 19% dietary level. Corn gluten feed was reported to have a high feed efficiency and resulted in cost effective rations without impairing fish growth (Wu et al., 1996; Tudor et al., 1996).
Channel catfish (Ictalurus punctatus) and hybrid catfish (Ictalurus punctatus x Ictalurus furcatus) fingerlings (50-60 g) could be fed on corn gluten feed up to 50% in channel catfish and up to 30% in hybrid catfish without impairing feed palatability, weight gain and feed efficiency (Robinson et al., 2001; Li et al., 2012). Corn gluten feed may also be beneficial to fish quality: it was shown to improve carcass yield and to reduce fattiness (Robinson et al., 2001). However, corn gluten feed offered to older fish (above 100 g) had very low DM digestibility (39%) and lysine was the first limiting amino acid (Kitagima et al., 2011).
The DM and energy of corn gluten feed were poorly digested by rainbow trout, but protein and fat digestibilities were high (92 and 90% respectively) (NRC, 1983 cited by Hertrampf et al., 2000).
NRC, 2001. Nutrient requirements of dairy cattle. 7th Revised Edition, Subcommittee on Dairy Cattle Nutrition, Committee on Animal Nutrition, Board on Agriculture and Natural Resources, National Research Council, National Academy Press, Washington, D.C.