Sustained hike in prices of traditional feed ingredients like cereal grains, protein meals and other feed commodities is forcing the animal nutritionist to find less expensive and safe alternatives to feed the animals. Corn is the most common and major feed ingredient used for both livestock and poultry, but its demand for human food, biofuel and bioindustrial products is not only increasing its cost, but also the availability of its by-products. Corn germ meal (CGM) is a by-product from corn industry obtained after extraction of corn oil and has nutritional characters (with medium energy and protein) for inclusion in livestock and poultry feeds. Nutritional value of CGM is strongly influenced by method of oil extraction apart from the effect of type of corn used. The main limiting factors to use CGM at higher quantities in animal or poultry diets include its high fibre, oil and phytate contents. Many research works have been conducted on the level of inclusion of CGM in the diets of cattle, sheep, pigs and poultry and its effect on their production performances in many parts of the world where the CGM availability through corn processing industries is more. In the recent past, Indian corn industry has been gaining importance resulting in production of CGM at appreciable quantities. In this regard, a review has been under taken compiling the recent studies and findings on nutritive value of CGM and its level of inclusion in livestock and poultry diets.
The total area under maize cultivation in the world is 159 million hectares with a production of 856 million metric tonnes (MMT) (FAO 2012). Major producers are USA (274MMT), China (208 MMT), Brazil (71 MMT), Mexico (22 MMT), and India (21 MMT). Although maize is the fifth largest cultivated cereal crop, it holds a record of being third largest among the total cereal crops yield. Over the past two decades, global maize production has increased by nearly 50% with an annual compound growth rate of 1.8%.
India is the fifth largest producer with a cultivated area of 8.4 million ha, and annual production of 21.10 MMT per year (FAO 2012). The average yield in India is 2.07 MT/ha. Andhra Pradesh is the leading producer (21%) in India followed by Karnataka (16%), Bihar, Maharashtra, Tamilnadu, Rajasthan, Madhya Pradesh and Gujarat. Maize is a multi utility grain with its use varying from feed to industrial products. The crop is primarily used as poultry feed (more than 50%) followed by human food (One-fifth), sparing the remaining for usage in breweries and preparation of industrial products. Predominantly, it is used as a basic raw material for the production of starch, oil, alcoholic beverages, food sweeteners and more recently in fuel industries. With the rapid hike in price of corn and soybean meal, poultry and dairy farmers are considering the usage of alternative ingredients like corn dried distiller’s grains, bakery by-products, glycerine and fractioned corn. There is a strong urge for the efficient usage of agroindustrial byproducts and/or non conventional feed resources available in the region, for the successful livestock and poultry sustainability at both regional and national level (Raju et al., 2017). Further, basic knowledge in level of inclusion, nutritive value, and deleterious factors present in ingredients is important while inclusion of these by-products in animal diets. Some alternative ingredients are not well studied and should be used with extreme caution. For instance, glycerine is still being studied as an energy source for swine and as per the available information it can be included at a maximum of 6% level because of the lack of nutritional knowledge behind the product in addition with feed flow ability issues at high inclusion levels. Indian corn industry is gaining importance resulting in the production of various by-products those have the potential to be used as animal feeds (corn gluten feed, gluten meal, germ meal, dry and wet distiller grain soluble). Out of these corn industry by-products, corn germ meal is being considered as a viable ingredient for all livestock species (Ewing, 1997). Hence a review has been undertaken here under regarding the recent studies and findings on nutritive value, level of inclusion in livestock and poultry diets and utilization constraints of CGM.
Production of CGM
Maize kernel is degerminated either by dry or wet milling processing to produce corn germ. Grain portion obtained after germ part removal is generally used to produce corn starch and ethanol. Among the starch, gluten and fiber portions recovered after degermination, gluten is used to extract corn gluten meal, where as starch undergoes liquefaction and saccharification followed by fermentation to produce ethanol and corn gluten feed on combining with fibers. The corn wet milling process consists of steeping the raw corn to moisten and soften the kernels, milling and then separating the kernel components through processes including washing, screening, filtering, and centrifuging. The primary end products obtained from corn wet milling are industrial corn starch (utilized for sweeteners), corn oil, and ethanol (Johnson and May 2003). Additional end products from the wet milling process include several feed co- products like dry corn bran, corn gluten feed, corn gluten meal, corn germ meal, and steep liquor or condensed fermented corn extractives (CFCE) (Loy and Wright, 2003). The feed co-products from corn wet milling account for approximately 30 percent of the raw corn input; nearly 66 percent of the corn kernel is actually converted into starch and 4 percent ends up as corn oil (Johnson and May, 2003). These co-products, however, are distinct entities compared to distiller grains, which are co-products from dry milling process. Corn germ, which contributes about 11% of the kernel weight, contains 45-50% oil and about 85% of the oil kernel (CRA, 2009; Albuquerque et al., 2014). Corn germ meal is the byproduct obtained by subjecting the corn germ to oil extraction. This meal contains 20 to 23 % of crude protein and the energy content varies with oil proportion which is further influenced by method of processing. Meal from corn germs is usually obtained by two ways i.e. expeller pressed (full-fat/ high-fat) and solvent extracted (less fat) forms; and corn germs are sometimes available, either from the wet milling or the dry milling process. As the germ portion from dry milling have not been subjected to steeping, dry milling product retains more soluble protein, phosphorus and starch than wet milling product.
Corn germ meal is usually palatable and can be used as an attractive medium protein and energy ingredient for many ruminant applications. Being rich in highly digestible amino acids, it offers a great alternative protein source for swine and poultry (Loy and Wright, 2003). In addition, the presence of hemi-cellulose fibers at higher levels delivers good hydration and pelleting characteristics.
The proximate composition of full fat and defatted CGM reported by various researchers are presented in Table 1. Corn germ meal is an extremely variable product and its chemical composition varies with method of oil extraction, variety of corn used, area of cultivation and climatic conditions. The protein, oil, fibre and starch content depend on the processes used for producing the germs, for extracting the oil, and on the amount of other maize by-products mixed with the spent germs. The residual oil, for instance, may be lower than 5% DM or higher than 14% DM, which is going to affect the energy value of the product. The ether extract value of CGM varies as low as 1.0 % in defatted CGM (Tekchandani et al., 1999) to as high as 17.32 in full fat corn germ (Widmer et al., 2008).
Table 1: Percent chemical composition of defatted and full fat CGM
|Reference||DM||TA||CP||EE||CF||NDF||ADF||Ca||P||MEK Cal/ Kg|
|Gupta et al. (1998)||–||–||24.69||5.68||7.56||–||–||–||–||–|
|Tekchandani et al. (1999)||95||0.38||22||1||12||–||14||0.04||0.5||1694|
|Moreira et al. (2002)||91.14||4.53||10.2||1.27||–||–||–||–||–||2949|
|Brunelli et al. (2006)||89.44||6.44||9.81||0.6||5.29||–||–||–||–||2413|
|Mendes et al. (2006)||89.67||3.9||12.4||1.6||–||37.6||7.3||–||–||3000|
|Beran et al. 2007)||88.03||7.35||10.79||0.2||–||–||–||–||–||–|
|Weber et al. (2010)||–||2.42||21||2.12||9.53||54.41||11.13||0.03||1.79||–|
|Almeida et al. (2012)||89.41||–||24.76||–||–||49.3||11.3||0.28||0.86||–|
|Full Fat CGM|
|Brito et al. (2005)||90||–||10.88||9.32||5.14||–||–||0.02||0.07||3350|
|Ramos et al. (2007)||88.28||2.62||10.13||9.96||2.18||30.25||9.09||0.02||0.41||3019|
|Widmer et al. (2008)||90.6||–||15.56||17.32||–||–||–||0.01||1.31||–|
|Calderano et al. (2010)||90.5||2.74||10.39||12.09||6.42||38.01||8.35||0.04||0.43||2832|
|Albuquerque et al. (2014)||96.39||1.87||11.48||49.48||–||–||–||–||–||–|
|Lakshmi et al. (2015)||91.4||2.44||21.13||10.85||13.56||–||–||0.34||0.62||–|
The protein quality and quantity of CGM mainly depends on oil content which varies with processing steps involved in oil production. Crude protein content of CGM varied from 10.13 (Ramos et al., 2007) to 24.79 (Almeida et al., 2012). Similarly, crude fibre composition of CGM showed a wide range from 2.18% (Ramos et al. 2007) to 21.07% (Prasad, 2011). The amino acid composition of CGM reported by various authors (Table 2) concluded that CGM is rich source of various indispensible amino acids like lysine, leucine, arginine and a poor source of tryptophan. Excess heat treatment during oil extraction in solvent extraction process can result in reduced digestibility of protein and some heat labile amino acids particularly lysine.
Table 2: Amino acid composition of CGM reported by various authors
|Reference||Indispensable AA%||Dispensible AA%|
|Tekchandaniet al. (1999)||1.3||0.7||0.7||1.8||0.94||0.6||0.9||1.1||0.2||1.2||1.4||1.4||0.4||3.2||1.1||1.3||1||0.7|
|*Kim et al.(2008)||1.12||0.42||0.42||0.98||0.8||0.27||0.56||0.53||0.14||0.73||0.88||1.15||–||1.88||–||0.89||0.57||0.4|
|*Widmer et al. (2008)||1.11||0.43||0.44||1.11||0.78||0.27||0.59||0.53||0.1||0.74||0.91||1.14||0.33||2.05||0.77||0.97||0.61||0.4|
|Weber et al. (2010)||1.49||1.17||0.64||0.75||1.7||1.04||0.37||0.89||0.78||0.63||1.26||1.5||–||0.33||2.87||0.91||1.07||0.2|
|Almeida et al. (2012)||1.55||0.64||0.84||1.86||0.94||0.4||1.04||0.83||0.18||1.3||1.38||1.68||0.33||2.84||1.23||1.09||0.8||0.7|
* Full fat corn germ meal
From the above table it can be observed that CGM either full fat or de-oiled is having good amino acid profile to be included in diets of swine and poultry. Various research work done to know the effect of either full fat or defatted CGM along with their levels of inclusion in diets of livestock and poultry were presented in Table 3.
Table 3: CGM level of inclusion in diets of livestock and poultry proposed by various authors
|Reference||Species||Level of Inclusion|
|Herold et al., 1998||Receiving calves||7% DM replaced with solvent extracted CGM|
|Herold et al., 1999||Finishing steers||15% CGM blended with 15% steep liquor|
|Ezequiel et al., 2006||Nellore steers||70% replacement of ground corn with CGM|
|Mendes et al., 2006||Rumen fistulated steers||11.6% of the diet|
|Kelzer et al., 2009||lactating Holstein cows||15% DM replaced with CGM|
|Moreira et al., 2002||Growing swine||3060 Kcal DE and 2,949 Kcal of ME/Kg of defatted CGM|
|Lopez et al., 2003||Growing swine||2,528 Kcal DE and 2,477 Kcal of ME/Kg, of Bran defatted CGM, and 40%|
|level of inclusion|
|Harbach et al., 2007||Swine||40% level of DCGM inclusion|
|Widmer et al., 2008||Growing swine||10% level of full fat CGM inclusion|
|Rojas et al., 2013||Swine||3150 Kcal ME/ kg DM of CGM|
|Brito et al.,2005a||Broilers of 8 to 21 days age||21.9% of corn replacement with CGM|
|22 to 38 days||22.5% of corn replacement with CGM|
|39day to slaughter||No restriction in level of CGM|
|Brunelli et al., 2006||Broilers||Up to 20% DCGM in total diet|
|Srtinghini et al., 2009||Broilers||21% and 16% replacement of sorghum with CGM in feeds containing ingredients of vegetable origin only and feeds with vegetable + animal origin respectively|
|Brunelli et al., 2012||Broilers||Up to 20% DCGM in total diet with phytase supplementation|
|Lakshmi et al., 2015||Colored broilers||Up to 25% CGM in total diet with phytase supplementation|
|Brunelli et al., 2010||Layers from 22 to 48 weeks age||Up to 21.2 % DCGM in total diet|
|Brito et al.,2005b||Layers from 30 to 60 weeks age||Up to 50 % DCGM in total diet|
|Brito et al., 2009||Layers from 78 to 90 weeks age||Up to 25 % replacement of corn with DCGM|
|Nizza et al., 2000||Rabbits||20% inclusion of CGM in the diet|
|Wang et al.,2010||Rabbits||5-10% inclusion of CGM in the diet|
|Nagpure, 2011||Broiler rabbits||10% inclusion of CGM in the diet|
|Habagonde, 2013||Broiler rabbits||17% inclusion of CGM in the diet|
CGM Inclusion in Ruminant Feed
Many authors tested CGM as a part of ruminant feed and its effect on nutrient digestibility and production parameters, and found that the positive effects of CGM on animal performance were due to the changes in microbial digestion pattern in rumen, passage rates of rumen contents, duodenal flows of different nutrients and associative effects on digestibility and absorbability of nutrients from other sources of diet.
Corn germ meal is an effective energy source for finishing cattle and can be partially replaced with ground corn in diets of Nellore steers raised under intensive system. Replacing 7% DM with solvent extracted CGM in calves’ diet heightened the performance of animals in terms of weight gain without any differences in intake of DM, CP, and NDF (Herold et al., 1998). They further determined that CGM contained about 40% undegraded protein intake (UIP) which is essential for high producing lactating cows. Mondal et al. (2008) revealed that CGM/maize oil cake contains 21% CP out of which 98% is slowly degradable fraction. They also concluded that effective dry matter degradability (EDMD) and effective crude protein degradability (ECPD) values of CGM were higher compared to other corn industry by-products.
Unaltered weight gain, feed conversion, and carcass dressing percentage were also observed when ground corn was partially replaced with CGM (Ezequiel et al., 2006). Besides, solvent extracted CGM had more favourable feed to gain ratio (5.04) when compared to corn bran (5.37) in diets of receiving calves (Herold et al., 1998). Mendes et al. (2006) stated that CGM provides adequate ruminal environment for microbial growth and microbial protein synthesis. They included CGM in the diets of ruminants and found unaltered ruminal microbial protein synthesis, feed passage rate, microbial composition, duodenal flows of organic matter, total carbohydrates, total nitrogen (N), microbial N, microbial efficiency and fluid dilution rate by the dietary composition. Kelzer et al. (2009) conducted an experiment to determine the effects of dried distiller grains plus soluble (DDGS), high-protein DDGS (HPDDGS), and dehydrated CGM by replacing 15% DM on feed intake, milk production, ruminal fermentation and digestibility in lactating Holstein cows and reported a higher DM intake, milk production and Milk urea nitrogen in treatment groups fed with HPDDG and CGM.
CGM Inclusion in Swine Feed
Corn germ meal was experimentally proved as a potential ingredient in swine diets. Incorporation of CGM at different levels in swine diets improved the growth performance, FCR and digestibility of nutrients, as well as carcass characteristics and meat quality of the pork. Defatted corn germ meal (DCGM) has digestibility and energy metabolization coefficients of 80.98 and 78.04 percentage, respectively, which corresponds to 3060 Kcal DE/Kg and 2,949 Kcal of ME/Kg on including in swine diet at growing phase (Moreira et al., 2002). Digestibility of hemicellulose was improved significantly by the Inclusion of CGM in the swine diets (Ziemer et al., 2008). Further, Lopez et al. (2003) evaluated the nutritive value of bran and defatted CGM by direct method in growing pigs and reported DE and ME values of 2,528 and 2,477 Kcal/kg, respectively. However, Rojas et al. (2013) reported a higher ME value of 3150 Kcal/ kg DM.
Feeding defatted CGM in diets of swine up to 40% had no negative effect on body weight gain and feed efficiency, but the digestibility of nutrients was reduced at highest level when five levels of corn replacement (0, 10, 20, 30 and 40%) was done with defatted CGM, which might be attributed to the phytate content of defatted CGM (Lopez et al., 2003). The Standardized Ileal Digestibility (SID) values for most amino acids in CGM were comparable or greater than those in corn, except for isoleucine, methionine and threonine which were more for corn (Petersen and Stein, 2009). Further, Almeida et al. (2011) reported apparent ileal digestibility and the Standardized Ileal Digestibility (SID) of CP and AA in corn germ meal in growing barrows and compared these values with the apparent ileal digestibility and SID of CP and AA in corn. They concluded that SID values for all indispensible AA in CGM were same as that of corn, except for arginine, histidine leucine and methionine, which were higher in corn.
Harbarch et al. (2007) found that the phytic acid present in CGM prevented pork lipid peroxidation when it was incorporated @ 10, 20 and 40% level of substitution in pig diets during 25 days preslaughter period. Additionally, they reported an inhibition of 63.0 percent on lipid peroxidation in the muscle from defatted CGM fed groups compared with control group, and concluded that CGM is responsible not only for prevention of lipid peroxidation in pork and also for increasing the shelf life of meat. Widmer et al. (2008) studied the effect of feeding full fat corn germ in growing pig diets and observed a linear increase in final body weights (P <0.05), lean meat percentage, iodine value of pork belly and a decrease in drip loss of pork as corn germ was included @ 5 and 10 percent levels in the diets.
The inclusion of increasing levels of defatted CGM in swine rations (0, 15, 30, and 45 percent) in the growing and finishing phase, leads to deterioration of the performance of animals, and reduces the back fat thickness without any influence on depth of the loin measured in live animal (Moreira et al. 2002). Furthermore, the economic analysis conducted by Moreira et al. (2002) considering the price of the defatted CGM as 80% of the price of corn revealed that the level of 15% of defatted CGM is the most economical for pigs at both growing and finishing phase, as no significant difference on the average cost per kg live weight gain was noticed between the two groups.
CGM Inclusion in Poultry Feed
Several trials have been conducted regarding the nutritive value of CGM, its suitability as feed ingredient for poultry, and economic feasibility as a poultry feed. Brito et al. (2005a) carried out two trials to evaluate the performance of broilers fed on increasing levels of CGM in the diets. The birds were allotted to a completely randomized design with four treatments (levels of CGM replacing corn in ration @ 0, 33, 67 and 100%), and reported that CGM was not a good ingredient for prestarter phase. The recommended percentage inclusion levels of CGM were 21.9 and 22.5 from 8 to 21, and 22 to 38 days, respectively. No restriction concerning the use of CGM for diets of broilers from 39 to 47 days of age was made. Defatted CGM (protein 11%, fat 1% DM) was found viable up to 20% level with no adverse effect on performance and carcass traits (Brunelli et al., 2006) on its inclusion @ 5, 10, 15 and 20% of corn soya based diets. Srtinghini et al. (2009) replaced sorghum in broiler diets with CGM and reported best performance at CGM inclusion rates of 21% and 15-16% in the diets containing ingredients from vegetable origin alone, and combination of vegetable and animal origin, respectively. Adding phytase to broiler diets including 20% defatted CGM had no effect on growth performance and carcass yield but increased oxidative stress (Brunelli et al., 2012). In this context, Lakshmi et al. (2015) reported that CGM inclusion up to 25% in diets of coloured broilers with or without phyatse enzyme supplementation had no effect on bird`s performance.
Brunelli et al. (2010) found that the increasing level of defatted CGM inclusion had a negative linear effect on feed intake and a quadratic effect on feed conversion ratio without significantly altering the other parameters; and concluded that defatted CGM can be included at levels up to 21.2% in diets of laying hens of 28 to 44 weeks age. Whereas birds fed with phytase in their diet showed improvement in yolk colour (Brunelli et al., 2012). The inclusion of 50% CGM (12% CP, 10% Fat) in layer diets (30 to 60 weeks) did not affect laying performance, egg quality and egg shell quality (Brito et al., 2005b). Similarly, Brito et al. (2009) evaluated the performance and egg quality of laying hens in second production cycle (78 to 90 weeks) by offering diets with CGM and recommended that corn can be safely replaced by substituting CGM up to 25% level without any negative effects on the birds’ performance. Rodrigues et al. (2001a) reported amino acid digestibilities of corn germ, fine corn germ and fat free corn germ as 91.5, 91.93 and 87.1 percent, respectively, in cecectomized adult cockerels. Kim et al. (2008) determined significantly higher true metabolizable energy (TMEn) and amino acid digestibility in CGM compared to high protein DDGS, while ‘Phosphorus’ bioavailability was significantly less for CGM (25 %) when compared to high protein-DDGS (60 % vs. 58 %, respectively). Brito et al. (2005a, 2009) reported that the diets formulated with the inclusion of CGM in the diets up to 22% and 25% are economical in broilers and layers at second productive cycle, respectively. However, Brunelli et al. (2006) concluded that inclusion of DCGM in diets of broilers up to 20% is economically unviable. The dissimilarities in economic efficiency of CGM included diets were mainly because of oil content of CGM that fixes the price of formulated diets.
CGM in Rabbit’s Diets
CGM is one of the most commonly used ingredient while formulating experimental and commercial diets of rabbits (Garcia et al., 2000; Nizza et al., 2000; Wang et al., 2010) with inclusion levels varying between 5 to 10% (Nicodemus et al., 2002; Wang et al., 2010). In an Italian study, incorporation of 20% CGM in rabbit’s diet slight improved the feed efficiency without any effect on growth rate and carcass traits compared to a control diet based on wheat products (Nizza et al., 2000). The protein of CGM is deficient in lysine (75% of requirements) and provides only 4-5% of sulphur amino acids and threonine above the requirements of growing rabbits. However, Nagpure (2011) conducted an experiment in growing broiler rabbits and concluded that CGM fed at 10% level to substitute 25% of GNC Protein in the diet improved broiler rabbit performance. In accordance to the previous study, Habagonde (2013) concluded that CGM can be fed up to 17% of broiler rabbit diet as 50% replacement of wheat bran.
Constraints of CGM Incorporation in Diets of Livestock and Poultry
Despite rich in nutritional content, incorporation of CGM at higher levels in swine and poultry diets is presumably restricted due to the higher phytate phosphorus (As the grain phosphorus is mainly stored in the germ portion and in corn it is mostly present in phytate form) and fiber content. Phytate phosphorus in CGM interferes with the digestion in the gut resulting in reduced digestibilities of nutrients when incorporated in the diets (Ravindran et al., 1999; Graf and Eaton, 1984). Rutherford et al. (1997) showed that free lysine in diet forms complexes with phytate; approximately 20 percent of free lysine will be in bound form and only half of this will get liberated through phytase addition.
Phytate is known to inhibit a number of digestive enzymes such as pepsin, amylase (Deshpande and Cheryan, 1984) and trypsin (Caldwell, 1992). Moreover, phytic acid is reported to form chelates with important metal ions, and decrease protein solubility at gut pH (Manez et al., 1999). The high fibre content of CGM is favourable for ruminants, but it restricts the usage of CGM at higher levels in the diets of poultry and swine. Further, the fat content of CGM determines its incorporation level in the ruminant diets as fat interferes with the digestion of fibre in the rumen there by reducing its nutritive value.
Scope of Future Research on CGM
A huge demand for alternative energy and protein sources as livestock and poultry diets exists due to the insufficient production and constant price escalation along with heavy competition of traditional feed ingredients with the human food and various biofuel industries. Corn gluten meal is already viewed as a valuable feed ingredient in pig, poultry and ruminant diets. Although, extensive research was conducted on CGM for feeding livestock and poultry, these products have not been fully adopted in the commercial feed industry. This phenomenon is likely due to the lack of consistency amongst the measured nutritive values of CGM, and hence variation exists in results from various feeding trials. Further, future research is necessary with higher level of inclusion of CGM in the diets of swine, poultry and ruminants with the help of biotechnological feed additives like employing phytase enzyme, various fibre degrading enzymes while making the diets economically feasible by eliminating or reducing the deleterious factors in CGM.
The maximum percentage level of CGM inclusion in layers, broilers, pigs, and ruminal diets is 50, 25, 40, and 15, respectively. Further research has to be continued to detect the proper amelioration of the anti nutritional factors present in CGM, so that more quantity can be incorporated without affecting the production performance while minimising the production cost.