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).
Palatability and feeding behaviour
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.
Wet corn gluten feed
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
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
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).