Impact of Dietary Crude Protein, Synthetic Amino Acid and Keto Acid Formulation on Nitrogen Excretion

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1 International Journal of Poultry Science (8): 49-46, 04 ISSN Asian Network for Scientific Information, 04 Impact of Dietary Crude Protein, Synthetic Amino Acid and Keto Acid Formulation on Nitrogen Excretion J.H. Kim, P.H. Patterson and W.K. Kim Poultry Science Division, National Institute of Animal Science, RDA, Cheoan 0-808, Republic of Korea Department of Animal Science, Pennsylvania State University, University Park, PA 680, USA Department of Poultry Science, University of Georgia, Athens, GA 060, USA Abstract: Nitrogen excretion from poultry facilities is one of the environment concerns. High levels of nitrogen excretion in poultry manure could cause eutrophication, nitrate or nitrite contamination in water, ammonia volatilization and acid deposition in the air. Therefore, minimizing nitrogen excretion in poultry manure is essential to maintain a clean environment. In order to minimize nitrogen excretion in manure, precise feed formulation to meet exact birds nutrient requirements is critical. In this study, an empirical exercise was conducted to evaluate the possibilities of supplementing hydroxy-analogues or keto acids into low protein diets to minimize dietary nitrogen and reduce nitrogen excretion in poultry manure. The results showed that supplementing synthetic amino acids to the 6% CP diet greatly reduced N input (.6% N) compared to a typical % CP corn and soybean meal diet supplemented with synthetic Met and Lys. Utilizing the three hydroxy-analogues with the 6% CP diet reduced nitrogen input further (approximately % more) compared to the 6% CP diet supplemented with synthetic amino acids. This empirical exercise showed the opportunities to reduce protein level and utilize synthetic amino acids, keto acids, or amino acid analogues to reduce nitrogen excretion. Key words: Feed formulation, keto acid, synthetic amino acids, hydroxyl analogue INTRODUCTION The negative influence of intensive poultry production on the environment has been a major issue facing the poultry industry (Blair et al., 999). High manure nitrogen excretion from poultry facilities could lead to eutrophication, nitrate/nitrite water contamination and ammonia emission and air pollution (Summers, 99; Moore, 998). Therefore, minimizing poultry manure nitrogen excretion is essential to maintain a clean environment. One of the strategies to reduce nitrogen excretion in poultry manure is minimizing excess protein and amino acid levels in diets. In this review, we discussed optimization of protein and amino acid input to meet the requirement using synthetic amino acids and keto-amino acids/hydroxyl-analogues. Empirical exercise: Three CP levels (, 9 and 6%) of corn and soybean meal diets were formulated using the Brill least cost feed formulation program. In all diets, dry matter was approximately 90%, metabolizable energy was, 00 kcal/kg, the minimum calcium was set at %, 0.45% available phosphorus and % linoleic acid. After formulation, levels of excess and limiting amino acids in the, 9 and 6% CP diets were compared with the amino acid requirements for broilers NRC (994). The composition of the diets are shown in Table -, respectively and the amino acid profile compared to the NRC amino acid requirements (994) for 0 to -wk-old broiler chicks are in Fig. -, respectively. The most limiting amino acid in the % CP corn and soybean meal diet was Methionine (Met) and the second most limiting amino acid was Lysine (Lys) (Fig. ). The diet with limiting amino acids should be supplemented with synthetic amino acids to maintain proper growth. However, there are several amino acids in excess compared to the NRC amino acid requirements (994) for broilers (Fig. ). The most excessive amino acid was Leucine (Leu) (70%) and the second most excessive amino acids were Glycine (Gly) and Serine (Ser) (57%) and Histidine (His) (5%). Phenylalanine (Phe) and Tyrosine (Tyr), Tryptophan (Trp), Valine (Val), Arginine (Arg), Isoleucine (Ile) and Threonine (Thr) were also greater than the NRC requirements (994) for broilers. Parr and Summers (99) also indicated that all essential amino acids except total sulfur amino acids of a % CP corn and soybean meal broiler diet were in excess of the NRC amino acid requirements (994) for broilers. These excess amino acids in the diet cannot be utilized for muscle accretion but instead are used for energy and fat deposition. Eventually, they increase nitrogen excretion in the manure. To reduce nitrogen excretion, the excess amino acids beyond the bird's requirements should be minimized. One method to minimize the excess amino acids is reducing crude protein level and supplementing synthetic amino acids or analogues of amino acids to meet the amino acid requirements. Corresponding Author: Woo Kyun Kim, Department of Poultry Science, Poultry Science Building 0, University of Georgia, Athens, Georgia-060, USA 49

2 Int. J. Poult. Sci., (8): 49-46, 04 Table : Composition of a % CP corn and soybean meal diet Amino acid composition Ingredient % % Corn 60.9 Arginine.450 Soybean meal.96 Glycine.08 Corn gluten.8 Serine 0.88 Animal vegetable fat.574 Glycine+Serine.965 Animal protein Histidine 0.57 Dicalcium phosphate Isoleucine 0.88 Limestone Leucine.04 Salt 0.00 Lysine.000 Vitamin premix 0.50 Methionine+Cystine 0.76 Phenylalanine.08 Metabolizable Phenylalanine+Tyrosine.946 Energy (kcal/kg) 00 Threonine 0.80 Crude protein.00 Tryptophan 0.48 Valine.055 Table : Composition of a 9% CP corn and soybean meal diet Amino acid composition Ingredient % % Corn Arginine.04 Soybean meal 9.70 Glycine.090 Animal vegetable fat.780 Serine 0.86 Animal protein Glycine+Serine.96 Dicalcium phosphate Histidine Limestone Isoleucine Salt 0.00 Leucine.756 Vitamin premix 0.50 Lysine Methionine+Cystine 0.66 Metabolizable Phenylalanine Energy (kcal/kg) 00 Phenylalanine+Tyrosine.586 Crude protein 9.00 Threonine Tryptophan 0.6 Valine.08 Table : Composition of a 6% CP corn and soybean meal diet Amino acid composition Ingredient % % Corn Arginine Soybean meal 6.6 Glycine Animal vegetable fat.789 Serine Animal protein.05 Glycine+Serine. Dicalcium phosphate.574 Histidine 0.84 Limestone.074 Isoleucine 0.59 Salt 0.00 Leucine.66 Vitamin premix 0.5 Lysine Methionine+Cystine 0.5 Metabolizable Phenylalanine Energy (kcal) 00 Phenylalanine+Tyrosine.46 Crude protein 6.00 Threonine 0.55 Tryptophan 0.85 Valine 0.7 When the CP level was empirically reduced from to requirements (994). Three amino acids were limiting in 9%, the amount of excess amino acids in the diet was the 9% corn and soybean meal diet compared to the reduced (Fig. ). The amino acids in greatest NRC amino acid requirements (994) for broilers: Met abundance were Gly and Ser (54%) and the second (74%), Lys (86%) and Thr (97%). Thus, these limiting most excessive amino acid was Leu (46%). The amino acids could be supplemented with synthetic percent amino acid concentrations of His, Val, Phe and amino acids or keto acids. Tyr, Ile, Trp and Arg were 8, 0, 8, 0, 08 and When the CP level of a diet was reduced to 6%, levels 04%, respectively, compared to the NRC amino acid of excess amino acids in the diet were considerably 40

3 Int. J. Poult. Sci., (8): 49-46, 04 amino acid (70%) in a % CP diet is now 4% of the NRC requirement (994). The levels of His, Gly+Ser and Phe+Tyr are 0, 05 and 05%, respectively, compared to the NRC requirements (994). These results suggest that the reduction of the CP level reduces excess amino acids, potentially decreasing nitrogen excretions in the manure. Furthermore, the reduction of CP level from to 6% created deficiencies of some amino acids that could be corrected with hydroxy-analogues or keto acids to meet the exact bird's requirements. The levels of Met+Cys, Lys, Thr, Val, Ile, Arg and Trp in the 6% CP diet were all less than that recommended by the NRC (994). Although all the limiting amino acids in a 9 or 6% CP diet could be supplemented by synthetic amino acids, the Met in the 9% CP diet and Met, Ile and Val in the 6% CP diet could be provided by hydroxy-analogues or keto acids. Lys and Thr cannot be synthesized from hydroxy-analogues or keto acids because there are no aminotransferases. Furthermore, there are no reports on the metabolism and utilization of hydroxy-analogues or keto acids of Arg and Trp in poultry. Therefore, there is only a limited opportunity to supplement the keto acids or hydroxy-analogues in feed formulation even if CP levels are reduced to 6%. However, hydroxy-analogues or keto acids of Met, Ile, or Val still can be supplemented in a 9 or 6% CP diet. Supplementing hydroxy-analogues or keto acids could reduce nitrogen excretion further compared to the 9 or 6% CP diet supplemented with only synthetic amino acids. The impact of hydroxy-analogue or keto acid supplementation on reducing N input in the diets was evaluated in Table 4 and 5. When the limiting amino acids, Met and Lys, in a % CP corn soybean meal diet were supplemented by synthetic amino acids, the total CP level was.%. When the CP level was reduced to 9% and the limiting amino acids, Met, Lys and Thr, were supplemented with synthetic amino acids, the total CP level was reduced to 9.%. When methionine-hydroxy-analogue (MHA) and two synthetic amino acids (Lys and Thr) were supplemented to the 9% CP diet, the total CP level was approximately 9.%. The 9% CP diet supplemented with synthetic amino acids reduced N input approximately 7.% compared to the % CP diet supplemented with synthetic amino acids, whereas MHA supplementation in the 9% CP diet did not have much impact on reducing N input further. When the dietary CP level was reduced to 6% and limiting amino acids were supplemented with synthetic amino acids to meet the NRC (994) requirement, the final CP level was reduced to 7.7%. When hydroxy- analogues or keto acids of Met, Ile and Val and synthetic amino acids of the remaining limiting amino acids were supplemented to the 6% CP diet, the total CP level was further reduced to 7.%. These results showed that Fig. : Amino acid concentration of a % CP corn and soybean meal diet compared to the NRC amino acid requirements (994) for broilers Fig. : Amino acid concentration of a 9% CP corn and soybean meal diet compared to the NRC amino acid requirements (994) for broilers Fig. : Amino acid concentration of a 6% CP corn and soybean meal diet compared to the NRC amino acid requirements (994) for broilers reduced compared to either the or 9% CP diets. In the 6% CP diet, there were not many amino acids in excess. The level of Leu that was the highest excessive 4

4 Int. J. Poult. Sci., (8): 49-46, 04 Table 4: Corn and soybean meal diets ( and 9%) CP supplemented with synthetic amino acids and hydroxy-analogues to meet the NRC (994) amino acid requirements for broilers Analogue, keto acid Total CP or synthetic amino acid levels (%) after supplementations in diets Supplementation level (%) supplemented After supplementing synthetic amino acids to the % CP diet CP level of basal diet.000 DL-methionine 0.9 CP level of DL-Met 0.08 L-lysine 0.00 CP level of L-Lys 0.0 Total CP level.0 After supplementing synthetic amino acids to the 9% CP diet CP level of the basal diet DL-methionine 0.8 CP level of DL-Met 0.09 L-lysine 0.56 CP level of L-Lys 0.87 L-threonine 0.05 CP level of L-Thr 0.08 Total CP level 9.4 After supplementing analogues and synthetic amino acids to the 9% CP diet CP level of the basal diet MHA 0.8 CP level of MHA L-lysine 0.56 CP level of L-Lys 0.87 L-threonine 0.05 CP level of L-Thr 0.08 Total CP level 9.05 MHA: Methionine hydroxy-analogue has an equal efficiency to DL-Met Table 5: Corn and soybean meal diets (6% CP) supplemented with hydroxy-analogues or keto acids and synthetic amino acids to meet the NRC (994) amino acid requirements for broilers Analogue, keto acid Total CP or synthetic amino acid levels (%) after supplementations in diets Supplementation level (%) supplemented After supplementing synthetic amino acids to the 6% CP diet CP level of the basal diet DL-methionine 0.89 CP level of DL-Met 0.8 L-lysine 0.4 CP level of L-Lys L-threonine 0.48 CP level of L-Thr 0.8 L-arginine 0.54 CP level of L-Arg 0.5 L-tryptophan 0.05 CP level of L-Trp 0.0 L-isoleucine 0.09 CP level of L-Ile 0.9 L-valine 0.87 CP level of L-Val 0.40 Total CP level 7.70 After supplementing analogues and synthetic amino acids to the 6% CP diet CP level of the basal diet MHA 0.89 CP level of MHA L-lysine 0.4 CP level of L-Lys L-threonine 0.48 CP level of L-Thr 0.8 L-arginine 0.54 CP level of L-Arg 0.5 L-tryptophan 0.05 CP level of L-Trp 0.0 HMV 0.49 CP level of HMV HIV 0.8 CP level of HIV Total CP level 7.0 After supplementing analogues, keto acids and amino acids to the 6% CP diet CP level of the basal diet MHA 0.89 CP level of MHA L-lysine 0.4 CP level of L-Lys L-threonine 0.48 CP level of L-Thr KGV 0.54 CP level of L-Arg Indole--pyruvate 0.05 CP level of L-Trp HMV 0.49 CP level of HMV HIV 0.8 CP level of HIV Total CP level MHA: Methionine hydroxy-analogue has an equal efficiency to DL-Met HMV: "-hydroxy-$-methylvanleric acid, hydroxy analogue of isoleucine, has 84% efficiency relative to L-Ile HIV: "-hydroxy-isovaleric acid, hydroxy analogue of valine, has 8% efficiency relative to L-Val 4 KGV: "-keto-*-guanido-0-valeric acid, keto acid of arginine, is assumed to have an equal efficiency relative to L-Arg 5 Indole--pyruvate: Keto acid of tryptophan is assumed to have an equal efficiency relative to L-Trp 4

5 Int. J. Poult. Sci., (8): 49-46, 04 Table 6: Total CP level of a 6% CP corn and soybean meal diet with supplemented synthetic amino acids to meet the digestible amino acid requirements based on the ideal protein ratio for broilers Limiting Digestible AA Digestible AA amino acid concentrations requirement in a 6% CP of limiting AA based on corn and soybean Amino acid Average in the 6% CP ideal protein meal diet concentration digestibility diet ratio % Methionine+Cystine Lysine Threonine Arginine Tryptophan Isoleucine Valine After supplementing only synthetic amino acids to the 6% CP diet (%) (%) CP level of the basal diet DL-methionine 0.60 CP level of DL-Met 0. L-lysine 0.5 CP level of L-Lys 0.65 L-threonine 0.64 CP level of L-Thr 0.94 L-arginine 0.54 CP level of L-Arg 0.50 L-tryptophan 0.00 CP level of L-Trp 0.00 L-isoleucine 0.8 CP level of L-Ile 0.46 L-valine 0.87 CP level of L-Val 0.40 Total CP level 7.80 Average true amino acid digestibility in a to % CP corn-soybean meal diet (Parsons, 99) Table 7: Total CP level of a 6% CP corn and soybean meal diet with supplemented hydroxy-analogues and keto acids to meet the digestible amino acid requirements based on the ideal protein ratio for broilers Limiting Digestible AA Digestible AA amino acid concentrations requirement in a 6% CP of limiting AA based on corn and soybean Amino acid Average in the 6% CP ideal protein meal diet concentration 6 digestibility diet ratio (%) After supplementing hydroxy-analogues and synthetic amino acids to the 6% CP diet CP level of the basal diet MHA 0.60 CP level of MHA L-lysine 0.5 CP level of L-Lys 0.65 L-threonine 0.64 CP level of L-Thr 0.94 L-arginine 0.54 CP level of L-Arg 0.50 L-tryptophan 0.00 CP level of L-Trp 0.00 HMV 0.59 CP level of HMV HIV 0.8 CP level of HIV Total CP level 7.0 After supplementing hydroxy-analogues, keto acids and synthetic amino acids to the 6% CP diet CP level of the basal diet MHA 0.89 CP level of MHA L-lysine 0.4 CP level of L-Lys 0.65 L-threonine 0.48 CP level of L-Thr KGV 0.54 CP level of L-Arg Indole--pyruvate 0.05 CP level of L-Trp HMV 0.59 CP level of HMV HIV 0.8 CP level of HIV Total CP level 7.0 MHA: Methionine hydroxy-analogue has an equal efficiency to DL-Met HMV: "-hydroxy-$-methylvanleric acid, hydroxy analogue of isoleucine, has 84% efficiency relative to L-Ile HIV: "-hydroxy-isovaleric acid, hydroxy analogue of valine, has 8% efficiency relative to L-Val 4 KGV: "-keto-*-guanido-0-valeric acid, keto acid of arginine, is assumed to have an equal efficiency relative to L-Arg 5 Indole--pyruvate: Keto acid of tryptophan is assumed to have an equal efficiency relative to L-Trp 6 Average true amino acid digestibility in a to % CP corn-soybean meal diet (Parsons, 99) 4

6 Int. J. Poult. Sci., (8): 49-46, 04 supplementing synthetic amino acids to the 6% CP diet ideal protein ratio are digestible amino acid greatly reduced N input (.6% N) compared to a typical requirements rather than total amino acid requirements % CP corn and soybean meal diet supplemented with like the NRC (994) requirements with intact protein. synthetic Met and Lys. Utilizing the three hydroxy- Thus, one can more precisely estimate the amount of analogues with the 6% CP diet reduced nitrogen input amino acid deficiency in order to supplement with further (almost %) compared to the 6% CP diet synthetic amino acids or keto acids. For instance, if supplemented with synthetic amino acids. limiting amino acids are supplemented with synthetic Although no actual studies have been conducted amino acids to meet the NRC (994) amino acid evaluating keto acid supplementation in reducing requirements, the amount of synthetic amino acids nitrogen excretion, several studies demonstrated that added to the diet is higher than the actual bird's synthetic amino acid additions to low protein diets requirements because the digestibility of synthetic significantly reduced nitrogen excretion in poultry amino acids (00%) is higher than the amino acid manure (Summers, 99; Blair et al., 999; Waldroup, digestibility (60 to 95%) of intact protein sources, such 000). Waldroup (000) reported that the chicks fed as soybean meal and corn. If we use the digestible either a 0. or 6.6% CP corn and soybean meal diet amino acid requirements based on the ideal protein supplemented with synthetic amino acids excreted ratio, estimated levels of limiting amino acids are the approximately.5 and 9.5% less nitrogen than those exact levels needed by the birds and can be met by fed the.48% CP basal diet, respectively. supplementing synthetic amino acids. Thus, using the The present empirical exercise indicated that digestible amino acid requirements based on the ideal supplementation of synthetic amino acids and keto protein ratio would be better than the NRC total amino acids to low protein diets could have an impact on acid requirements for supplementing synthetic amino nitrogen excretion in poultry manure by reducing N input. acids or keto acids in low protein diets. An example of Although no feeding trials have been conducted to supplementing synthetic amino acids, keto acids and evaluate the utilization of hydroxy-analogues or keto analogues based on the ideal protein ratio approach to acids of Arg and Trp in poultry, their addition to low a low CP diet is shown in Table 6 and 7. protein diets would reduce N input further if the hydroxy- Concentrations of amino acids in a 6% corn and analogues or keto acids are effectively converted to the soybean meal diet were converted to digestible amino corresponding amino acids. Some studies have been acid levels based on average digestibility of each amino conducted to evaluate replacement of Arg and Trp by acid (Parson, 99). Then, the digestible amino acid their corresponding hydroxy-analogues or keto acids in levels in the 6% CP diet were subtracted from the the diets of rats. Winitz et al. (957) reported that rats fed digestible amino acid requirement based on the ideal an arginine-deficient diet supplemented with the keto protein ratio in order to estimate the amount of synthetic acid of Arg, "-keto-*-guanido-0-valeric acid, had higher amino acid or keto acid supplementation. weight gain than those fed the arginine-deficient diet. When limiting amino acids in the 6% CP diet were The efficiency of "-keto-*-guanido-0-valeric acid was supplemented with only synthetic amino acids to meet approximately 74% of L-Arg. Pond et al. (964) indicated the digestible amino acid requirements based on the that the hydroxy-analogue (DL--indole lactic acid) of Trp ideal protein ratio, the total CP level was 7.8%. When promoted rat growth equal to that achieved with DL-Trp, the three hydroxy-analogues of Met, Ile and Val were whereas the keto acid (-indole pyruvic acid) had supplemented instead of amino acids, the total CP level approximately 80% efficiency relative to DL-Trp and 7% was reduced to 7.%. When the three hydroxyrelative to L-Trp. analogues and two keto acids of Arg and Trp were It is necessary to evaluate the transamination of the keto added to the 6% CP diet, the total CP level was acids of Arg and Trp in poultry. If the keto acids of these reduced to 7.%. However, each of these total CP amino acids are effectively transaminated, their addition levels was higher than those of the 6% CP diet to low protein diets could reduce N input further. Thus, supplemented with synthetic amino acids or keto acids the total CP level of the 6% CP diet supplemented with based on the NRC (994) amino acid requirements. the hydroxy-analogues and keto acids was also This result was contrary to what was expected. It was estimated with the assumption of equal efficiencies of expected that supplementing synthetic amino acids or keto acids of Arg and Trp relative to L-Arg and L-Trp in keto acids to the low protein diet to meet the digestible Table 5. This reduced the final CP level further to amino acid requirements based on the ideal protein approximately 7.%. ratio would reduce N input further compared to the NRC Utilizing the Ideal Protein Ratio concept might reduce N amino acid requirement basis. One of explanations for input further because it makes a better amino acid this is that the total requirements for key amino acids balance and eliminates excesses of amino acids based on the ideal protein ratio are higher than the NRC compared to the NRC (994) amino acid requirements. amino acid requirements for broilers (994). The total Furthermore, the amino acid requirements based on the amino acid requirements which are converted from the 44

7 Int. J. Poult. Sci., (8): 49-46, 04 digestible amino acid requirements based on the ideal no intention to lose optimum bird performance. protein ratio for Lys, Met+Cys, Thr, Val and Arg were., Moreover, the cost of supplementing keto acids and 0.9, 0.85, 0.96 and.6, respectively, whereas the NRC synthetic amino acids into poultry diets is very expensive, requirements of those amino acids were.0, 0.90, e.g., the prices of soybean meal, synthetic valine and the 0.80, 0.90 and.5, respectively. Thus, we have to add reagent grade keto acid of valine are $ 0.,.70 and more synthetic amino acids or keto acids to meet the 4.80/kg, respectively. A few synthetic amino acids can ideal amino acid requirements compared to the NRC be supplemented into poultry diets on a cost-effective (994) amino acid requirement basis. basis including Met, Lys, Thr and Trp (Waldroup, 000). The ideal amino acid requirements may overestimate Only the hydroxy-analogue of Met can be supplemented actual amino acid requirements for broilers in intact into poultry diets in a cost effective manner today. protein diets. Because the ideal amino acid Although the poultry industry will not use expensive keto requirements were made based on purified diets, acids and synthetic amino acids into poultry diets right application of the ideal amino acid requirements to intact now, it could be more feasible in the future when protein feed formulations like corn and soybean meal environmental regulations are more restrictive and diets might not be effective. Wang and Fuller (990) also fermentation technologies allow for less expensive keto indicated that the ideal amino acid ratios developed acids and synthetic amino acids. using purified diets might not be applicable to practical intact protein diets. In purified diets, the changes of Conclusion: This empirical exercise showed the amino acid levels affect bird performances more opportunities to reduce protein level and utilize synthetic sensitively than those in intact protein diets. Thus, using amino acids, keto acids, or amino acid analogues to the ideal amino acid requirements for corn and soybean reduce nitrogen excretion. Actual feeding trials with meal diet formulations might not be a good method to poultry need to be conducted to evaluate the effect of reduce N excretion by supplementing synthetic amino keto acid and amino acid analogue supplementation acids or keto acids in low protein diets. Therefore, the into low protein diets on nitrogen excretion and growth diet formulation based on the NRC (994) amino acid performance of poultry. requirements would be more effective for supplementing synthetic amino acids or keto acids to reduce N input. Although lowering the CP level to 6% markedly reduced N input compared to the % CP diet, the 6% CP diet is too low to maintain proper growth even if all limiting amino acids are supplemented to the NRC requirement REFERENCES Blair, R., J.P. Jacob, S. Ibrahim and P. Wang, 999. A quantitative assessment of reduced protein diets and supplements to improve nitrogen utilization. J. Appl. Poult. Res., 8: (994). Edmonds et al. (985) demonstrated that chicks Edmonds, M.S., C.M. Parsons and D.H. Baker, 985. fed a synthetic amino acid supplemented 6% CP corn Limiting amino acids in low protein corn-soybean and soybean meal diet significantly improved weight meal diets fed to growing chicks. Poult. Sci. 64: gain compared to those fed an unsupplemented 6% CP diet, but did not fully reach the weight of chicks fed a Moore, P.A. Jr., 998. Best management practices for 4% CP diet. 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The effects of CP diet supplemented with synthetic amino acids had minimizing amino acid excesses in broiler diets. similar body weights and significantly less manure N Poult. Sci., 70: excretion (.6% reduction) compared to those fed a Parsons, C.M., 99. Amino acid digestibilities for.48% CP diet. However, if the crude protein level is poultry: Feedstuff evaluation and requirements. higher than 6% in a corn and soybean diet, the Pages -5, in: BioKyowa Technical Review-, opportunity for the supplementation of hydroxyanalogues or keto acids is further reduced. Supplementing hydroxy-analogues or keto acids to low, 6% CP diets is currently not feasible for the poultry industry even though this feeding practice could markedly reduce nitrogen excretion in poultry manure. One of the reasons is because the poultry industry has Nutri-Quest, Inc., Chesterfield, MO. Pond, W.G., L.H. Breuer, Jr., J.K. Loosli and R.G. Warner, 964. 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8 Int. J. Poult. Sci., (8): 49-46, 04 Summers, J.D., 99. Reducing nitrogen excretion of the Wang, T.C. and M.F. Fuller, 990. The effect of the plane laying hen by feeding lower crude protein diets. of nutrition on the optimum dietary amino acid Poult. Sci., 7: pattern for growing pigs. Anim. Prod., 50: Waldroup, P.W., 000. Feeding programs for broilers: Winitz, M., J.P. Greenstein and S.M. Birnbaum, 957. The challenge of low protein diets. pp: 9-4 in: Quantitative nutritional studies with water-soluble, Proceedings of 47th Maryland Nutrition Conference chemically defined diets. V. Role of the isomeric for Feed Manufacturers. University of Maryland, arginines in growth. Arch. Biochem. Biophys., 7: College Park, MD