A total of five studies were conducted to determine the nutritional value of co-products of bioethanol production for poultry and pigs. The objective in the first study was to evaluate the relationship between the chemical components of maize- and wheat distillers dried grains with solubles (DDGS) as well as develop prediction equations for indispensable amino acids (IAA), total indispensable amino acid (TIAA) and total amino acid (TAA) contents using nutrient composition data available in literature. The relationship between the chemical constituents of maize- and wheat-DDGS and associated probability values were determined by correlation analysis. Prediction models for determining the IAA, TIAA and TAA contents of maize- and wheat-DDGS from their crude protein (CP) and amino acids (AA) contents were developed using step-wise multiple regression analyses. Maximum improvement in adjusted r2 (adj r2) and reduction in Mallows Cp were the model selection criteria. The chemical composition of maize- and wheat-DDGS varied among sources with coefficient of variation (CV) ranging from 8.5% to 53.5% for total P and Ca respectively in maize-DDGS and 10.5% to 36.1% for CP and acid detergent fibre (ADF) in wheat-DDGS respectively. Of the IAA, Lys, Met and Trp were most variable in maize-DDGS with CV of 13.1%, 12.0%, 10.3%, respectively, whereas Lys, Phe and Met were the most variable IAA in wheat-DDGS with CV of 20.2%, 17.3%, and 16.9%, respectively. For maize-DDGS, there were positive correlations (P < 0.05) between CP and CF, NDF, Ca, ash (r ranged from 0.45 and 0.61). Adjusted r2 ranged from 0.57 to 0.99 in the best models for predicting the IAA in maize- and wheat-DDGS from CP and AA. Except for Trp and Lys, the IAA contents of maize- and wheat-DDGS can be predicted from their CP content alone. The best models for predicting TIAA and TAA in maize-DDGS included Arg, His and Leu (adj r2= 0.98) and His, Leu and Trp (adj r2= 0.90) respectively, the regression equations being TIAA (% DM) = 0.77 + 1.36 (Arg) + 3.87 (His) + 1.99 (Val) and TAA = -3.03 + 14.1 (His) + 3.79 (Leu) + 23.4 (Trp) respectively. For wheat-DDGS, the best three variables for predicting TIAA were Arg, Leu and Val (adj r2=0.99), the regression equation being TIAA (% DM) = -0.07 + 1.11 (Arg) + 0.99 (Leu) + 5.02 (Val). Predicted values were close to actual values in the prediction models for IAA, TIAA and TAA. It was concluded that the IAA, TIAA and TAA contents of both maize- and wheat-DDGS can be predicted from their CP contents with high accuracy. In the second study, the nutritional value of wheat-DDGS without- or with exogenous enzymes for broiler was determined using three experiments. The N-corrected- and apparent metabolisable energy contents (AMEn and AME, respectively) without- or with added admixture of xylanase, amylase and protease (XAP) was determined in experiment 1, true P digestibility without- or with supplemental phytase was determined in experiment 2, whereas the apparent- or standardised ileal digestibility (AID and SID, respectively) of AA without- or with added protease was determined in experiment 3. Birds were fed a nutrient adequate pre-experimental diet from d 1 to 14 post-hatch followed by the dietary treatments from d 14 to 21 in experiment 1 and 2, or from d 25 to 28 in experiment 3, respectively. Each of the 3 experiments was arranged as a randomised complete block design consisting of 7 replicate pens and 3 birds per pen. Six dietary treatments consisting of 3 levels of wheat-DDGS (0, 300 or 600 g/kg of diet) and 2 levels of XAP (0 or 0.25 g/kg) were used in experiment 1. Six diets consisting of 3 levels of wheat-DDGS (200, 400 or 600 g/kg of diet) and 2 levels of phytase (0 or 1000 FTU/kg) were used in experiment 2, whereas four treatments consisting of a nitrogen-free diet (NFD) and an assay diet, both diets without- or with supplemental protease were used in experiment 3. In experiment 1, increasing the level of wheat-DDGS in the basal diet decreased linearly (P < 0.001) dry matter (DM) and energy retention, AME and AMEn. Supplemental XAP tended to improve both the dietary AME (P = 0.059) and AMEn (P = 0.085) values of the diet. The AME value of wheat-DDGS without- or with supplemental XAP was determined to be 15.0 or 15.5 MJ/kg, respectively. Corresponding values for AMEn were 14.0 and 14.5 MJ/kg, respectively. Supplemental XAP did not improve the energy value of wheat-DDGS for broilers. In experiment 2, increasing the level of wheat-DDGS in the diet decreased linearly (P < 0.05) ileal DM digestibility, DM retention and apparent P retention but there was no difference in apparent ileal P digestibility. Except for Fe and Zn at the ileal, and Mn and Zn at the total tract level, increasing the level of wheat-DDGS in the diet increased linearly (P < 0.05) the flow of all other minerals. Flow of minerals at the ileal and total tract level were not different with phytase supplementation. True ileal P digestibility in the wheat-DDGS for broilers was 93.6 or 96% without- or with added phytase, respectively. Corresponding values at the total tract level were 92.4 and 93.5%, respectively. Phytase addition did not improve P utilisation at the ileal or total tract level. In experiment 3, AID ranged from 33% (Asp) to 75% (Pro) without added protease whereas the range was 31% (Asp) to 82% (Pro) with protease supplementation. The AID of Lys was nil regardless of protease supplementation. Supplemental protease improved (P < 0.05) the AID of Arg and Pro and tended to improve (P < 0.10) the AID of Met. Without protease supplementation, SID ranged from 43% (Asp) to 84% (Pro) whereas the range was from 54% (Asp) to 93% (Pro) with added protease. Supplemental protease improved (P < 0.05) the SID of Arg, Leu, Phe, Met, Val and Pro by 21, 14, 13, 26, 13 and 10 percentage points, respectively. It was concluded that wheat-DDGS is a good dietary source of metabolisable energy and P for broilers. The ileal AA digestibility of wheat-DDGS for broilers is quite variable and generally low. Further, the ileal digestibility of some AA in the wheat-DDGS improved with protease supplementation.Using three experiments the third study determined the metabolisable energy content, true P digestibility and retention and AIAAD and SIAAD of wheat-DDGS for turkey. The AMEn and AME content of wheat-DDGS without- or with XAP was determined in experiment 1, the true P digestibility and retention without- or with supplemental phytase was determined in experiment 2, whereas the AIAAD and SIAAD of wheat-DDGS without- or with a protease were determined in experiment 3. Experiment 1 and 2 lasted for 21 days whereas experiment 3 lasted for 28 days. Experimental diets were fed for 7, 5 or 3 d in experiment 1, 2 or 3, respectively. Each of the 3 experiments was arranged as a randomised complete block design consisting of 7 replicate pens and 3 birds per pen. Six dietary treatments consisting of 3 levels of wheat-DDGS (0, 300 or 600 g/kg of diet) and 2 levels of XAP (0 or 0.25 g/kg) were used in experiment 1. Six diets consisting of 3 levels of wheat-DDGS (200, 400 or 600 g/kg of diet) and 2 levels of phytase (0 or 1000 FTU/kg) were used in experiment 2, whereas four diets consisting of a NFD and an assay diet, both diets without- or with supplemental protease were used in experiment 3. In experiment 1, increasing the dietary inclusion of wheat-DDGS from 0 to 600 g/kg decreased linearly (P < 0.05) DM and energy retention. There was wheat-DDGS × XAP interaction (P < 0.05) for dietary AME and AMEn. Dietary AME and AMEn values decreased linearly (P < 0.001) as the level of wheat-DDGS increased in the diets without XAP, whereas there was no effect of increasing wheat-DDGS level on dietary AME or AMEn for the XAP-supplemented diets. From the regression of wheat-DDGS-associated energy intake (MJ) against wheat-DDGS intake (kg), the AME values (MJ/kg of DM) of wheat-DDGS without- or with supplemental XAP were determined to be 14 or 14.9, respectively. Corresponding AMEn values (MJ/kg of DM) were 13 and 13.8, respectively. Supplemental XAP did not improve the energy value of wheat-DDGS for turkey. In experiment 2, increasing the dietary inclusion level of wheat-DDGS decreased linearly (P < 0.05) DM intake, ileal DM digestibility and DM retention. Apparent ileal P digestibility and apparent P retention were not affected by either wheat-DDGS inclusion level or phytase supplementation. Except for Mn and Zn, flow of minerals at either the ileal or total tract level increased linearly (P < 0.05) with graded levels of wheat-DDGS in the diet. Flow of minerals (Cu, Fe, Mg, Mn, K, Na, Zn) at the ileal or total tract level (mg/kg of DM intake) were not different with phytase supplementation. True ileal P digestibility was determined to be 75.8% or 82.1% for wheat-DDGS without- or with supplemental phytase, respectively. Respective values at the total tract were 70.7% and 81.6%. In experiment 3, the ileal digestibility of Lys was zero regardless of protease supplementation. Apparent ileal digestibility was lower than 50% for all AA except for Glu (70%) and Pro (81%) in the wheat-DDGS without supplemental protease. Also, SIAAD ranged from 41% (Thr) to 89% (Pro) without added protease whereas the range was from 56% (Arg) to 88% (Pro) with added protease. With the exception of Cys and Pro, supplemental protease increased (P < 0.05) the AIAAD and SIAAD of all other AA from between 5 to 19 percentage points. It was concluded that wheat-DDGS is a good source of metabolisable energy and P for turkey. The ileal digestibility of AA in wheat-DDGS is generally low. In addition, supplemental protease improved the ileal digestibility of majority of the AA in the wheat-DDGS for turkey. The metabolisable energy, digestible AA and P values of wheat-DDGS determined and reported in the second study were used in a fourth study to formulate diets for broilers. These diets were used to determine the effect of XAP or phytase added individually or in combination on growth performance, jejunal morphology, intestinal pH and caecal volatile fatty acids (VFA) production in broilers receiving a wheat-SBM based diet containing wheat-DDGS. Two hundred and eighty-eight 1-d old broiler chicks were allocated to eight dietary treatments in a randomized complete block design consisting of 6 replicate pens and 6 birds per pen. The treatments were 1) a positive control (PC1); wheat-soyabean meal (wheat-SBM) diet and adequate in metabolisable energy (ME) and all nutrients, 2) a second positive control (PC2); wheat-SBM based diet containing wheat-DDGS and adequate in ME and all nutrients; 3) a negative control (NC1) marginal in ME (minus 0.63 MJ/kg), 4) NC1 plus XAP added to provide per kg of diet, 2000, 200 and 4000 U of xylanase, amylase and protease, respectively 5) a negative control (NC2)marginal in available P (minus 0.15%) 6) NC2 plus phytase added to provide 1000 FTU per kg of diet, 7) a negative control (NC3) that is low in ME and available P (minus 0.63 MJ/kg and 0.15%, respectively), 8) NC3 plus a combination of XAP and phytase at the rates in diets 4 and 6, respectively. Wheat-DDGS was included in the diet at the rate of 12, 22 or 25% at the starter (d 1 to 10), grower (d 11 to 24) or finisher (d 25 to 42) phases. Reducing the ME and non-phytate P in the NC diets depressed (P < 0.05) bodyweight gain (BWG), final bodyweight (FBW) and gain:feed (G:F) compared with the PC diets. From d 1 to 24, birds receiving the PC diet containing wheat-DDGS were heavier and consumed more (P < 0.01) compared with birds receiving the PC diet containing no wheat-DDGS. An admixture of XAP improved (P ≤ 0.05) BWG and G:F above the NC1 diet from d 1 to 24 whereas supplemental phytase had no effect on growth performance. From d 25 to 42, BWG and FBW did not differ between the birds receiving the PC1 and PC2 diets, but G:F was superior (P < 0.01) for birds receiving the PC1 diet. From d 1 to 42, addition of XAP improved (P < 0.05) G:F and tended to improve (P < 0.10) BWG above the NC diet. Further, performance responses did not differ between birds receiving the PC2 and XAP diet. Inclusion of wheat-DDGS in the diet reduced (P < 0.05) digesta pH at the caeca, but pH did not differ among treatments at the duodenum. Volatile fatty acids production in the caeca was not affected by either XAP or phytase supplementation, but wheat-DDGS reduced (P < 0.05) the production of n-butyric acid. Jejunal villi height was not different among the dietary treatments but XAP increased crypt depth. In conclusion, the addition of an admixture of XAP to a wheat-SBM based diet containing wheat-DDGS produced modest improvements in the growth performance of broilers whereas phytase had no effect. There is substantial data about the nutritional value of maize- and wheat-DDGS for pigs but there is no information about the effect of dietary fibre type on nutrient digestibility due to differences in the chemical characteristics of the protein feedstuff used. The fifth study determined the effect of dietary fibre type and protein level on ileal amino acids digestibility for growing pigs. Twenty boars (Yorkshire × Landrace) with average initial bodyweight of 35 kg and fitted with a simple T-cannula at the terminal ileum were used in the current study. The dietary treatments were three fibre types (SBM, canola meal (CM) or maize-DDGS) and two levels of CP (adequate (18%) or reduced (14%)). In each period, two pigs with bodyweights closest to the mean bodyweight of the twenty pigs were offered a nitrogen free diet to determine basal endogenous ileal amino acid flow. The remaining eighteen pigs were allocated to the experimental diets using a replicated 6 × 2 Youden square design. Ileal digesta was collected for two days in each period after five days of adaptation to the diet. In comparison, AIAAD for the SBM diet were greater (P < 0.05) compared with the CM diet except for Met, Trp, Cys and Pro. Apparent ileal digestibility of DM, Gly and Asp were greater (P < 0.05) for the SBM diet compared with the maize-DDGS diet. The AID of the following AA were greater in the maize-DDGS diet compared with the CM diet: Ile, Leu, Phe, Val, Ala, Tyr and Asp. There was fibre type × protein level interaction (P < 0.05) for the AID of Lys because in the CP-adequate diets, the AID of Lys differed (P < 0.05) amongst the dietary fibre sources, whereas the AID of Lys was not different in low-CP diets. The SIAAD of the SBM diet was greater (P < 0.05) than those of the CM diet for all AA except for Trp and Pro, whereas Gly and Asp were more digestible (P < 0.05) in the SBM diet compared with the maize-DDGS diet. Standardised ileal digestibility of the following AA was greater in the maize-DDGS diet compared with the CM diet: Ile, Leu, Val, Ala, Tyr and Asp. Reducing dietary protein level by 4% did not affect DM utilisation or the AID or SID of N and AA in the current study. It was concluded that the choice of protein feed ingredient used in swine diets in relation to the fibre composition affects ileal amino acids digestibility. Furthermore, AA digestibility is not affected by a 4% reduction in dietary crude protein level for growing pigs.Collectively, it was concluded from these experiments that mathematical models are a useful tool to predict the amino acids content of maize- and wheat-DDGS. The ME in wheat-DDGS was comparable to those of wheat and maize grain for broilers and turkey, therefore, wheat-DDGS may be used as a substitute for wheat or maize in diets for broiler and turkey. The digestible P content in wheat-DDGS for broilers and turkey is greater than in most other major feedstuffs. The use of wheat-DDGS in poultry diet may therefore reduce the quantity of inorganic P compounds used, reduce P loss in manure and overall may reduce feed cost. Ileal AA digestibility in the wheat-DDGS for broilers and turkey was variable and generally low. It was recommended that the low digestibility of essential AA in wheat-DDGS should be accounted for when using wheat-DDGS as a feedstuff for poultry. Although maize-DDGS contain greater levels of fibre, ileal AA digestibility are similar to that of SBM for pigs but CM was inferior to the other two protein sources. The differences in fibre characteristics of protein feedstuffs affects ileal AA digestibility.
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The nutritional value for poultry and pigs of biofuel co-products
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