A study was carried out to find out the chemical composition, mineral profile, Cornell net carbohydrate and protein system (CNCPS) fractionations and in vitro digestibility of nutrients among different samples of corn dried distiller grain solubles (DDGS), collected from five ethanol processing industries of Andhra Pradesh. The mean CP, CF, EE, and TA of various DDGs samples were, 28.92, 7.68, 11.86, and 5.75, respectively. Similarly the calcium, phosphorous, sodium, potassium, magnesium and sulfur content of DDGs were 0.3, 0.61, 0.32, 0.82, 0.27, and 0.78, respectively. CNCPS fractionations revealed that DDGS can be effectively used as superior quality carbohydrate and protein source. The average in vitro digestibility coefficients of DM, CP, NDF and ADF were, 71.45, 78.96, 70.42, and 63.36%, respectively. Significant difference among the nutrient digestibility of samples studied by in-vitro digestibility and CNPS fractionation may be attributed to difference in processing procedures followed by the industrial plants.
Distiller’s grains with soluble (DDGs) are the nutrient rich co-product of dry-milled ethanol production. India stands at seventh position in DDGS production (Renewable Fuels Association, 2015). As the dairy farmers are able to avail the DDGs at a very cheap price, there is an increasing trend in the usage of DDGs as animal feed. The high energy, protein, and phosphorus content of DDGS makes it a very important partial substitute for some of the more expensive traditional energy (maize), protein (soybean meal), and phosphorus (mono or di-calcium phosphate) ingredients used in animal feeds (U.S grain Council, 2012) and can be replaced at higher proportions. But, lack of knowledge on nutritive value variations of DDGS often leads to imprecise diet formulation. Therefore, the objective of the study was to characterize the variability in chemical composition, mineral profile, CNCPS fractions and in-vitro nutrient digestibility of corn DDGS for ruminants available at various ethanol plants in Andhra Pradesh.
Materials and Methods
Five different DDGs feed samples were collected from the selected ethanol plants (from Nandyala, Vijayawada, Visakhapatnam, Chittoor and Kakinada regions) of Andhra Pradesh, India. Representative samples (triplicates) from each ethanol plant were processed for chemical analysis, mineral profile, CNCPS fractions and in vitro digestibilities. Proximate analysis was done as per AOAC (2007), and forage fiber fractions according to Vansoest et al. (1991). Calcium and phosphorus were determined according to the methods described by Talapatra et al. (1940). Sodium and potassium; magnesium and sulfur were estimated by using flame photometer and gravimetric methods, respectively. Estimation of starch in dried samples was done as per the procedure of Sastry et al. (1991). Non-structural carbohydrates (NSC) were derived as per the equations given by Van Soest et al. (1991). The carbohydrate fractions (A, B1, B2 and C) for different DDGS samples were estimated using the procedures of Sniffen et al. (1992). Primary protein fractions were estimated as per the procedures of Licitra et al. (1996) and Sniffen et al. (1992). The DDGs samples were evaluated for in vitro DM, CP, NDF and ADF digestibility (Tilley and Terry, 1963) by incubating 0.5 gms feed samples for 72 h at 39oC in buffered rumen liquor collected from rumen fistulated buffalo bull. The in vitro digestibility of organic matter (IVDOM), metabolizable energy (ME) and net energy for lactation (NEL) were calculated according to Menke and Steingass (1988), as follows-
IVDOM (%) = 9 + 0.9991×G24 + 0.595×CP + 0.181×CA;
ME (MJ/Kg DM) = 1.06 + 0.157× G24 + 0.08 ×CP + 0.22×EE – 0.081×CA;
NEL (MJ/Kg DM) = -0.36 + 0.1149×G24 + 0.054×CP + 0.139×EE – 0.054×CA.
(Where CP, CA and EE were in % DM and G24 in ml/200 mg DM)
All the data generated was subjected to ANOVA (Snedecor and Cochran, 1994) using software package SPSS version 17.0, and differences in mean were assessed by using Duncan’s multiple range test (Duncan, 1955).
Results and Discussion
The proximate and cell wall constituents and mineral composition of the DDGS samples are presented in Table 1. The mean concentrations of nutrients in DDGS in the present study were similar to the published data (MNC, 2001; NRC, 1982). The DDGs samples differed non-significantly (P>0.05) for its chemical composition and cell wall constituents, except total ash (P<0.05). However, significance in chemical composition of DDGs was reported by Waldroup et al. (2007); and Stein et al. (2009). Belyea et al. (2004) reported that the variability in DDGs composition might be due to processing differences among plants, and also variability in the input corn composition. The mineral composition of various DDGs samples collected from different plants differed significantly (P<0.01), except magnesium (P>0.05).
Table 1: Chemical composition of the DDGS samples (% DM basis)
|Crude Protein (CP)*||28.92||30.2||29.2||0.55|
|Crude Fiber (CF)*||7.68||8.8||9.8||0.23|
|Ether Extract (EE)*||11.86||10.9||11.8||0.16|
|Total Ash (TA)*||5.75||5.8||5.8||0.21|
|Nitrogen Free Extract (NFE)*||45.78||–||–||0.12|
|Neutral Detergent Fiber (NDF)*||42.34||–||–||0.87|
|Acid Detergent Fiber (ADF)*||22.08||–||–||0.75|
**(p<0.05) *(p < 0.01) 1Minnesota Nutrition Conference 2National Research Council
The minerals values were in corroboration with those reported by Klopfenstein (2001). The variation of Ca and Na contents in DDGS might be due to the addition of exogenous sources added to adjust pH, or to optimize enzyme and yeast performance and also while sanitation of process in ethanol production (Liu and Han, 2011). Sulfur content in the DDGs samples tested was almost two times higher than the values indicated by the NRC (2001) which may be attributed to usage of sulphuric acid during buffering process. Although, Song et al. (2012) showed that high sulfur content in corn DDGS may be beneficial in avoiding metabolic oxidation imbalance in swine; sulfur levels greater than 0.4 % of diet DM from feed can cause polioencephalomalacia in cattle, and can interfere with copper absorption and metabolism, which can be alleviated by dietary copper supplementation (Boyles, 2007). DDGs tested in this study contains higher phosphorus and low calcium and supplemental calcium sources must be added to the diet to maintain a calcium to phosphorus ratio between 1.2:1 to not more than 7:1 to avoid reductions in animal performance. The variation in mineral content of the DDGs depends upon the corn composition and mineral availability in soil where the respective plant grows. Lack of variation in Mg concentrations among samples could reflect the reduced influence or lack thereof of processing techniques and conditions on the DDGS studied.
The values of structural, non-structural carbohydrates (NSC) and different fractions i.e. fraction A (fast degradable), B1 (Intermediate degradable), B2 (Slow degradable) and C (unable cell wall) are presented in Table 2. As almost all of the starch in corn is converted to ethanol during the fermentation process, the fat and fiber concentrations in DDGS increased by a factor of three compared to corn (Shurson and Noll, 2005). Further, the high amounts of NDF makes DDGS a highly digestible fiber source for cattle, and reduces digestive upsets compared to corn when fed to animals. Consequently, the high digestible fiber in corn DDGS allows it to serve as a partial replacement for forages and concentrates in diets for dairy and beef cattle. In addition its high fat content renders the usage of DDGs as a high-energy feed stuff. The buffer soluble protein fractions of different DDGS samples are depicted in Table 2. The NDIN and ADIN content of the sample was 47 and 12 % of the CP respectively.
Strong negative relationship existed between ADIN and N digestibility in ruminant diets, as the ADIN is assumed to be completely unavailable to the animal (Yu and Thomas, 1976; Licitra et al., 1996). So, the presence of low amount of ADIN in DDGs indicates the higher protein digestibility. Among the protein fractions, B2+B3 fraction was higher and A+B1 was lower, indicating that it could be used as a source of bypass protein (Sharma et al., 2004; Klopfenstein, 2001). The CNCPS fractional variations depend upon the extent of heat treatment and charring of the corn during processing. Mild heat treatment may increase the PB2 and PB3 fractions and so the rumen inertness. Similarly, excessive charring may increase the PC and CC fractions leading to lesser digestion and absorption of the byproduct.
Table 2: Carbohydrate and Protein Components in the DDGS Samples
|NDICP (% CP)||27.14||0.49|
|ADICP (% CP)||7.04||0.21|
|BIP (% CP)*||82.74||0.78|
* (P<0.05), CHO – Carbohydrate, NSC – Non structural Carbohydrate, CA – Carbohydrate fraction A, CB1 – Carbohydrate fraction B1, CB2 – Carbohydrate fraction B3, CC – Carbohydrate fraction C, NDICP – Neutral detergent insoluble crude protein, ADICP – Acid detergent insoluble crude protein, NPN – Non protein Nitrogen, SP – Soluble Protein, BIP – Borate insoluble Protein, PA – Protein fraction A, PB1 – Protein fraction B1, PB2 – Protein fraction B2, PB3 – Protein fraction B3, PC – Protein fraction C
In vitro Nutrient Digestibility
The in vitro digestibility values of five DDGS samples are presented in Table 3. The average in vitro digestibility of DM, CP, NDF and ADF was 71.45, 78.96, 70.42, and 63.36, respectively. The mean DM digestibility observed in the present study was correlated with those values given by Woods et al. (2003), Sauvant et al. (2004) and NRC (2001).
However, Birakelo et al. (2004) reported higher DM digestibility than the value observed in the present study. Similar to this study, higher fiber digestibility was observed by Al-Suwaiegh et al.(2002) and Varga and Hoover (1983). The higher fibre digestibility in DDGS samples was due to the ethanol fermentation process that renders it more soluble and fermentable in ruminants (Walter, 2010). Moreover, less starch in the ration may lead to higher rumen pH, favorable for cellulolytic bacterial growth (Orskov 1988; Martin et al., 1999). The energy values of DDGs were expected to be lower than that of corresponding original maize grains due to an increase in fibre fractions and reduction in starch after ethanol production. However, Nuez-Ortı´n and Yu (2009) found that different types of DDGS were similar or superior to their respective raw materials in terms of energy values for ruminants.
Table 3: Nutritive Value, In vitro Digestibility and Gas Production Characteristics of the DDGS Samples
|Gas Produced (ml/200mg)||47.34||0.51|
|ME (MJ/Kg DM)||13.06||0.11|
|NEL (MJ/Kg DM)||7.98||0.08|
* (P<0.05), IVOMD – In vitro OM digestibility, ME – Metabolisable Energy, NEL – Net energy for Lactation, IVDMD – In vitro DM digestibility, IVCPD – In vitro CP digestibility, IVNDFD – In vitro NDF digestibility, IVADFD – In vitro ADF digestibility
It can be concluded that the variations among nutrient constituents of DDGs samples were negligible and means of nutrient composition DDGs studied were in agreement with the values reported earlier. Further, In-vitro nutrient digestibility and CNCPS fractionation revealed that DDGS can be effectively used as superior quality fiber and bypass protein source.
The Authors are highly thankful to the Departments of Animal Nutrition, SVVU, Gannavaram and PVNRVU, Rajendranagar for providing necessary facilities to carry out this research.