Use of Digestible Amino Acids and the Concept of Ideal Protein in Feed Formulation for Broilers

2005 Poultry Science Association, Inc. Use of Digestible Amino Acids and the Concept of Ideal Protein in Feed Formulation for Broilers R. L. Dari,* A. M. Penz Jr.,*, A. M. Kessler, and H. C. Jost Nutron Alimentos Ltd., Campinas, SP, Brazil 13091-611; and Departmento de Zootecnia, Universidade Federal do Rio Grande do Sul, Porto Alegre-RS, Brazil 91540-000 Primary Audience: Nutritionists, Researchers SUMMARY The objective of this study was to evaluate diet formulation based on digestible amino acids (DAA), the formulation of low protein diets supplemented with synthetic amino acids, and L-Thr supplementation to increase the Thr:Lys ratio from 67:100 to 70:100. Two experiments were carried out with Hubbard male broilers from 3 to 6 wk of age. In experiment 1, corn-soybean meal diets containing 20% CP were used. In experiment 2, 20% CP diets were formulated with corn, soybean meal, wheat bran, feather meal, and meat meal. In both experiments, body weight gain and economic evaluations were better for broilers fed diets formulated on DAA. Carcass yields and carcass composition were not significantly affected by formulation procedures. In experiment 2, birds fed diets based on DAA had improved feed efficiency compared with those fed total amino acids (TAA). In experiment 1, a reduction of CP from 20 to 18.2% did not affect broiler performance. It did, however, result in fatter carcasses, lower percentages of breast meat, and lower economic evaluation. In both experiments, performance and economic evaluation were not affected by the Thr:Lys ratio. In experiment 1, however, abdominal fat and carcass fatness were reduced, and, in both experiments, carcass protein level was higher with a Thr:Lys ratio of 70:100 than with 67:100 ratio (P < 0.05). Key words: broiler, amino acid, digestible amino acid, protein, ideal protein, carcass composition, formulation 2005 J. Appl. Poult. Res. 14:195 203 DESCRIPTION OF PROBLEM There are very few comprehensive studies testing the use of digestive amino acids (DAA) under practical conditions. However, some work demonstrates better broiler performance when DAA levels are taken into consideration in feed formulation [1, 2, 3, 4]. The interest in DAA formulation arises from advantages of feeding chickens less dietary pro- tein to support the desired performance. Some of these advantages are maximization of the use of these amino acids (AA) for protein synthesis and not as energy source, decreased environmental pollution, reduced feed cost, and decreased requirements for the limiting amino acid. On the other hand, some researchers conclude that it is impossible to determine the requirements for each DAA under each specific field situation due to the large number of environmental, health, 1 To whom correspondence should be addressed: rdari@nutron.com.br.

196 nutritional, genetic, and even market factors that interact and interfere with the determination of an optimal level for each AA in the diet. As a solution for part of this problem, the concept of ideal protein was conceived in which the requirements of all essential DAA are given as percentages of the digestible Lys requirement [5]. Two experiments were carried out to test the hypothesis of the efficiency of amino acid (AA) digestibility coefficients in feed formulation. In experiment 1, low CP diets, based on corn and soybean meal, were tested. In experiment 2, complex diets, containing ingredients with lower AA digestibility, were tested. The possibility of reducing CP level in diets formulated to supply AA requirements through the use of synthetic AA was evaluated. We verified the efficiency of using the DAA ratio, according to ideal protein for broilers proposed in studies by Baker and Han [6]. MATERIALS AND METHODS A total of 2,880 male 1-d-old Hubbard chicks was used. During the initial phase, chicks were fed a starter diet and water ad libitum. At 21 d of age, birds were individually weighed and separated into 4 weight groups. Then, 30 birds were distributed per box and received experimental diets. Each treatment had 8 replicates (2 replicates of each weight group). Experiment 1 Six diets based on corn and soybean meal were formulated; the compositions are presented in Table 1. Treatment 1 (T1), used as control, was formulated to contain digestible LYS and sulfur amino acids (SAA) in the ratio recommended by Illinois ideal protein for broilers (IICP [6]) or SAA equal to 75% of Lys. The other nutrient levels were established according to NRC [7]. Treatment 2 (T2) was different from the control in L-Thr supplementation, aiming at supplying Thr as a proportion of Lys level, according to IICP (Thr:Lys, 70:100). Treatments 3 and 4 (T3 and T4, respectively) were different from the control as they were formulated to supply 18.2% CP. This level was chosen because under 18.2% CP, Trp level is marginal according to the NRC [7]. The difference between T3 and T4 JAPR: Research Report was that T3 was formulated based on total amino acids (TAA), containing the same total Lys, SAA and Thr levels as the control (T1), and treatment T4 was formulated based on DAA, containing the same digestible LYS, SAA, and THR levels as the control (T1). Treatments 5 and 6 (T5 and T6) were similar to T3 and T4 but used T2 as a reference not T1. Hence, T5 had the same TAA levels as T2 and T6 and the same DAA levels as T2. Experiment 2 Diets for T1 and T2 were same as T1 and T2 in experiment 1 (Table 1). Treatments 3 to 6 (T3, T4, T5 and T6) contained 6.5% wheat bran, 5.0% meat meal, and 5.0% feather meal in addition to corn and soybean meal. Treatments 3 and 4 had the same nutrient levels as T1, but T3 was formulated on a TAA basis and supplied the same total Lys, SAA, and Thr levels as T1. Treatment 4 was formulated on a DAA basis to provide the same digestible Lys, SAA, and Thr levels as T1. Treatments 5 and 6 were similar to T3 and T4 but used T2 as reference not T1. Hence, T5 had the same TAA levels as T2 and T6 and the same DAA levels as T2. The levels of DAA in the ingredients were obtained by multiplying TAA (Table 2) analyzed levels by their respective coefficients of digestibility according to the tables published by Heartland Lysine, Inc. [8] (Table 3). The average weight gain, feed intake, feed conversion (FC) and FC adjusted for the same weight gain (AFC) were determined for each replication. The adjustment of the AFC was made by using an equation that gives the FC as a function of the body weight. For each replication a specific equation was calculated using data of body weight and FC measured weekly. At 42 d of age, 2 birds from each experimental unit were selected within the range of average weight for the pen ± 10 g and slaughtered to evaluate carcass composition. Carcass yield (CARCY), (carcass weight as a % of body weight), breast yield (BY) and deboned breast yield (DBY), abdominal fat deposition (AF), including fat around the gizzard (all expressed as a % of carcass weight) were determined. The bioeconomic index (BEI) [9] was used to evaluate the effect of the different diets on the ratio of feed cost to revenue generated per bird.

DARI ET AL.: FEED FORMULATION FOR BROILERS 197 TABLE 1. Composition of diets of experiments (Exp) 1 and 2 Exp 1 and 2 Exp 1 Exp 2 T1 1 T2 T3 T4 T5 T6 T3 T4 T5 T6 Corn (8.9% CP) 61.38 61.39 64.47 64.46 64.47 64.46 64.10 64.09 64.10 64.09 SBM (45.5% CP) 31.79 31.74 26.63 26.75 26.58 26.71 13.80 13.68 13.75 13.64 Wheat bran (13.3% CP) 6.50 6.50 6.50 6.50 Meat meal (57.0% CP) 5.00 5.00 5.00 5.00 Feather meal (80.1% CP) 5.00 5.00 5.00 5.00 Soybean oil 3.75 3.75 3.75 3.75 3.75 3.75 3.75 3.75 3.75 3.75 Dicalcium phosphate 1.17 1.17 1.21 1.21 1.21 1.21 0.11 0.11 0.11 0.11 Limestone 1.20 1.20 1.24 1.24 1.24 1.24 0.87 0.87 0.87 0.87 Salt 0.32 0.32 0.32 0.32 0.32 0.32 0.16 0.16 0.16 0.16 Premix 2 0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.26 DL-Met 0.13 0.13 0.20 0.18 0.20 0.18 0.06 0.11 0.06 0.11 L-Lys HCl 0.18 0.15 0.18 0.15 0.27 0.28 0.27 0.28 L-Thr 0.03 0.09 0.07 0.11 0.09 0.02 0.04 0.05 0.06 Caulin 0.01 1.65 1.61 1.68 1.63 0.10 0.15 0.12 0.17 Calculated nutritional composition (%) ME (kcal/kg) 3,100 3,100 3,100 3,100 3,100 3,100 3,100 3,100 3,100 3,100 CP (%) 20.0 20.0 18.2 18.2 18.2 18.2 20.0 20.0 20.0 20.0 Analyzed CP (%) 19.0 18.6 17.6 17.5 18.6 18.2 18.6 18.5 17.9 18.5 Calcium (%) 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Analyzed calcium (%) 0.78 0.77 0.76 0.74 0.84 0.74 0.95 0.95 0.91 0.97 Available phosphorus (%) 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 Analyzed phosphorus (%) 0.48 0.49 0.47 0.46 0.47 0.47 0.56 0.54 0.54 0.54 Sodium (%) 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Analyzed sodium (%) 0.15 0.14 0.14 0.13 0.16 0.13 0.13 0.13 0.12 0.14 Choline (mg/g) 1.57 1.57 1.44 1.45 1.44 1.45 1.35 1.35 1.35 1.35 Total Lys (%) 1.10 1.10 1.10 1.07 1.10 1.07 1.10 1.10 1.10 1.10 Digestible Lys (%) 0.91 0.91 0.94 0.91 0.95 0.91 0.91 0.91 0.91 0.91 Total Met + Cys (%) 0.81 0.81 0.81 0.80 0.81 0.80 0.81 0.86 0.81 0.86 Digestible Met + Cys (%) 0.68 0.68 0.70 0.68 0.70 0.68 0.63 0.68 0.63 0.68 Total Thr (%) 0.75 0.78 0.75 0.74 0.78 0.76 0.75 0.77 0.78 0.80 Digestible Thr (%) 0.61 0.64 0.63 0.61 0.65 0.64 0.60 0.61 0.62 0.64 1 T = treatment. 2 Supplied per kilogram of diet: vitamin A, 7,000 UI; vitamin D3, 1,400 UI; vitamin E, 20 mg; vitamin K 3, 1.5 mg; vitamin B 1, 0.6 mg; vitamin B 2, 5.0 mg; vitamin B 6, 0.6 mg; vitamin B 12,10µg; pantothenic acid, 10 mg; niacin, 23 mg; folic acid, 0.25 mg; biotin, 20 µg; choline, 300 mg; Fe, 25 mg; Zn, 40 mg; Mn, 60 mg; Cu, 6 mg; I, 0.38 mg; Se, 0.18 mg; growth promoters: virginiamycin, 20 ppm, and furamisol, 25 ppm; and anticoccidiostat: salinomycin, 60 ppm.

198 JAPR: Research Report TABLE 2. Analyzed values (%) of amino acids for feather meal, meat and bone meal, corn, soybean meal, and wheat bran Feather meal Meat meal Corn Soybean meal Wheat bran Lys 2.64 2.97 0.26 2.95 0.48 Met 0.92 0.80 0.19 0.65 0.18 Cys 3.59 0.48 0.18 0.78 0.28 Thr 3.72 1.75 0.29 1.81 0.39 Trp 0.60 0.35 0.05 0.67 0.15 BEI = weight gain (feed cost/live broiler market price) feed consumption. To analyze body composition, birds were frozen and ground in a meat grinder to obtain a homogeneous mass, from which a sample of approximately 250 g was taken to determine moisture, CP, and crude fat (CF) of the carcasses [10]. The CF level was determined in 20 carcasses, chosen as representative, to obtain the prediction equation of CF levels of the remaining carcasses. CF = 76.66 0.471(H) 1.753(CP); r 2 = 0.52. RESULTS AND DISCUSSION Experiment 1 The reduction of CP from 20 to 18.2% (Table 4, contrast 1) did not significantly (P > 0.05) influence bird performance. Diets with 18.2% CP had increased (P = 0.08) feed intake, caused exclusively by increased feed intake for diets formulated on a DAA basis. Similar results have been observed in previous studies [11, 12]. On the other hand, Reginatto [13], working with diets with ME:CP ratios of 160 to 181 during the grower stage (22- to 42-d-old birds), found that the reduction in CP dietary levels impairs broiler performance, despite maintaining uni- form Lys and DAA levels. All studies found in the literature in which CP levels were reduced kept TAA levels constant. The reduction of CP from 20 to 18.2%, but maintaining the same TAA levels in the T3 and T5 diets, produced lower weight gain and feed intake than the T4 and T6 diets, which had the same DAA levels as the T1 and T2 diets, respectively (Table 4, contrast 2). FC and AFC were not influenced by the treatments. These results are rather surprising as the T3 and T5 diets had higher digestible SAA, Lys, and Thr levels than the T4 and T6 diets, respectively (Table 1). It was expected that birds on T3 and T5 would have the same performance as those on T4 and T6. Some studies suggest that the DAA requirements are related to the level of dietary CP [14, 15]. A reduction in the CP level would also reduce DAA requirements. According to this, SAA, Lys, and Thr requirements for birds fed T3, T4, T5, and T6 diets (with 18.2% CP) should be lower than those for birds fed the T1 and T2 diets (with 20% CP). If this reduction in DAA requirements really occurred, added to the fact that T3 and T5 diets contained higher levels of DAA than T1 and T2, it is possible that there was a disproportion among DAA that impaired bird performance due to excessive SAA, Lys, and Thr levels relative to the other AA. The CARCY was not influenced by treatments. However, the 18.2% CP level caused TABLE 3. True digestibility (%) of essential amino acids for poultry 1 Ingredient Lys Met Cys Thr Corn 80.8 91.4 82.9 82.6 Soybean meal (44%) 83.4 82.6 73.8 80.9 Wheat bran 74.7 79.3 75.7 74.6 Meat meal 74.5 80.9 57.6 74.2 Feather meal 65.2 74.4 62.0 73.6 1 Heartland Lysine Inc. [8].

DARI ET AL.: FEED FORMULATION FOR BROILERS 199 TABLE 4. Performance (21 to 42 d of age), carcass composition and bioeconomic index of broilers in experiment 1 18.2% CP 20.0% CP Thr + Thr F-test for contrasts 3 Thr 1 + Thr 2 Total Dig 4 Total Dig Level of significance Performance T1 T2 T3 T4 T5 T6 C1 C2 C3 CV (%) Weight gain, g 1,539 1,518 1,509 1,538 1,505 1,550 0.804 0.010 0.706 2.5 Feed intake, g 3,154 3,171 3,186 3,210 3,150 3,214 0.082 0.020 0.731 1.6 Feed conversion (feed/gain) 2.05 2.09 2.11 2.09 2.09 2.07 0.160 0.192 0.870 2.3 Adjusted feed conversion 2.05 2.10 2.12 2.09 2.11 2.07 0.252 0.112 0.783 2.9 Carcass composition (%) Carcass yield 74.96 74.92 74.97 75.14 75.09 75.33 0.605 0.638 0.792 1.6 Boned breast yield 22.09 21.75 20.89 21.17 21.59 21.51 0.035 0.766 0.602 4.4 Breast meat yield 17.76 17.41 16.86 17.13 17.24 17.51 0.058 0.253 0.517 3.8 Abdominal fat 2.53 2.43 2.99 3.04 2.73 2.38 0.046 0.617 0.023 17.9 Moisture 63.61 63.27 61.26 62.48 62.66 63.01 0.014 0.105 0.180 2.1 Carcass crude protein 16.76 17.23 16.65 16.82 17.03 17.12 0.638 0.546 0.033 3.5 Carcass crude fat 17.34 16.84 18.36 17.77 17.29 16.99 0.090 0.192 0.007 5.4 Economic evaluation Bioeconomic index 11.92 10.81 9.87 10.86 9.93 10.94 0.006 0.011 0.289 9.6 1 Thr = without Thr supplementation to increase the Thr:Lys ratio. 2 + Thr = with Thr supplementation to increase the Thr:Lys ratio to 70:100. 3 Contrasts (C): C1 = treatment (T) 1 and T2 vs. T3, T4, T5, and T6 (20% CP vs. 18.2% CP); C2 = T3 and T5 vs. T4 and T6 (formulation based on total amino acids vs. digestible amino acids); C3 = T1, T3, and T4 vs. T2, T5, and T6 (Thr supplementation according to NRC [7] vs. Baker and Han [6]). 4 Dig = digestible.

200 lower BY and higher AF. Although not statistically significant, DBY was also decreased due to a reduction in CP level (Table 4, contrast 1). The reduction of dietary CP level from 20 to 18.2% promoted lower carcass moisture level. Carcass protein was not influenced by treatments, and, despite the low statistical significance, abdominal fat increased (P = 0.09) as the level of dietary CP decreased. These results are consistent with those obtained by Reginatto [13], who observed that diets with reduced CP levels produce carcasses with a higher percentage of fat and lower percentage of protein. The increase in AF caused by 18.2% CP diets agrees with results published by other authors [15, 16], who reported a reduction in CP level causes an increase in ME:CP ratio, which was 155 in 20% CP diets and increased to 170 in 18.2% CP diets in our study. Moreover, body fat level is highly influenced by the nutritional diet composition. Fat deposition in the carcass increases as the ME:CP ration increases [17, 18]. In this experiment, CP level was reduced, but SAA, Lys, and Thr levels were kept constant in the diets. In the literature, all studies show that DAA supplementation of low protein diets is not enough to decrease AF in birds. Formulation based on DAA or TAA did not significantly influence (P > 0.05) carcass yield or carcass composition (Table 4, contrast 2). Economic evaluation indicated that there was a highly significant (P < 0.01) reduction in BEI promoted by the decrease in diet CP (contrast 1). This CP reduction impaired BEI, particularly due to the lower economic evaluations of the T3 and T5 diets as a consequence of lower weight gain and higher feed intakes as compared with the T4 and T6 diets (Contrast 2). Contrast 3 compared T1, T3, and T4, formulated to supply Thr requirements according to the NRC [7], with T2, T5, and T6, formulated to contain Thr in the adequate ratio in relation to Lys level according to Baker and Han [6]. Contrast 3 was not significant for any performance parameter or for CARCY, BY, DBY, or BEI (P > 0.05). However, there was a significant (P < 0.05) reduction in AF. Carcass composition was also significantly influenced by the increase in Thr levels in T2, T5, and T6 as compared with T1, T3, and T4. The CP level increased JAPR: Research Report and CF level decreased when the Thr:Lys ratio was increased from 67:100 to 70:100. Experiment 2 The inclusion of ingredients with less digestible AA to diets significantly (P < 0.01) influenced bird performance (Table 5, contrast 1). The T1 and T2 diets, containing only corn and soybean meal, promoted better weight gain, FC, and AFC than the T3, T4, T5, and T6 diets, which all contained 6.5% wheat bran, 5.0% feather meal, and 5.0% meat meal. On the other hand, there was no significant effect on feed intake. Formulation based on DAA significantly improved performance for diets containing ingredients with lower AA digestibility compared with formulations based on TAA (Contrast 2). T3 and T5 diets, which had the same total SAA, Lys, and Thr, levels as corn-soybean meal diets, T1 and T2, respectively, resulted in lower weight gain, feed intake, FC, and AFC than T4 and T6, formulated on a DAA basis and which contained the same SAA, Lys, and Thr as T1 and T2, respectively. The T3, T4, T5, and T6 diets, containing 6.5% wheat meal, 5.0% feather meal, and 5.0% meat meal, promoted higher CARCY than the T1 and T2 diets, which were based on cornsoybean meal. However, those diets caused higher AF and lower BY and DBY. Rostagno et al. [4] also observed a lower percentage of breast with skin and bones and higher AF with the inclusion of low AA digestibility plant and animal ingredients in diets. However, they did not find changes in CARCY. The inclusion of lower AA digestibility ingredients caused lower moisture and CP and higher CF in bird carcass (contrast 1). The diet formulation on a DAA basis did not have a significant effect on carcass composition parameters in broilers consuming diets with lower AA digestibility ingredients as compared with those fed diets formulated on TAA basis (contrast 2). These results differ from those obtained by Rostagno et al. [4] for BY. In that study, there was a significant increase of 0.6% in the percentage of breast meat with skin and bones due to DL-Met and L-Lys supplementation in low digestibility ingredients to match digestible SAA and Lys levels of the control diet based

DARI ET AL.: FEED FORMULATION FOR BROILERS 201 TABLE 5. Performance (21 to 42 d of age), carcass composition and bioeconomic index of broilers in experiment 2 CS + alternative ingredients 2 CS 1 Thr + Thr F-test for contrasts 5 Thr 3 + Thr 4 Total Dig 6 Total Dig Level of significance Performance T1 T2 T3 T4 T5 T6 C1 C2 C3 CV (%) Weight gain 1,539 1,518 1,451 1,518 1,469 1,516 0.001 0.0002 0.862 2.3 Feed intake 3,154 3,171 3,125 3,199 3,146 3,170 0.874 0.015 0.824 1.7 Feed conversion 2.05 2.09 2.15 2.11 2.14 2.09 0.001 0.007 0.671 2.2 Adjusted feed conversion 2.05 2.10 2.18 2.12 2.17 2.10 0.001 0.004 0.583 2.7 Carcass composition (%) Carcass yield 74.96 74.92 76.02 76.31 76.52 75.63 0.032 0.881 0.632 2.3 Boned breast yield 22.09 21.75 21.20 21.29 21.22 20.94 0.035 0.511 0.808 5.2 Breast meat yield 17.76 17.41 16.92 16.99 16.75 16.78 0.006 0.288 0.856 4.6 Abdominal fat 2.53 2.43 3.01 3.05 3.27 2.96 0.001 0.847 0.528 17.9 Moisture 63.61 63.27 62.24 61.68 61.83 61.23 0.002 0.304 0.616 2.48 Carcass crude protein 16.76 17.23 16.43 16.78 16.89 16.82 0.072 0.600 0.022 2.72 Carcass crude fat 17.34 16.84 18.55 18.21 17.75 18.47 0.004 0.656 0.309 6.49 Economic evaluation Bioeconomic index 11.92 10.81 10.88 11.55 10.84 11.58 0.611 0.044 0.180 8.5 1 CS = corn-soybean meal based diet. 2 CS + alternative ingredients = diet with wheat bran, meat and bone meal and feather meal. 3 Thr = without Thr supplementation to increase the Thr:Lys ratio. 4 + Thr = with Thr supplementation to increase the Thr:Lys ratio to 70:100. 5 Contrasts (C): C1 = treatment (T) 1 and T2 vs. T3, T4, T5, and T6 (corn-soybean meal based diets vs. complex diets); C2 = T3 and T5 vs. T4 and T6 (formulation based on TAA vs. DAA); C3 = T1, T3, and T4 vs. T2, T5, and T6 (Thr supplementation according to NRC [7] vs. Baker and Han [6]). 6 Dig = digestible.

202 JAPR: Research Report on corn-soybean meal. On the other hand, there was no effect of the formulation based on DAA on CARCY and AF in that study [4]. Economic evaluation through the BEI showed that the inclusion of lower AA digestibility ingredients in T3, T4, T5, and T6 did not significantly influence profitability of the activity as compared with T1 and T2, based on cornsoybean meal (contrast 1). The DAA-based formulation had a significant effect on the BEI (contrast 2). The T3 and T5 diets, formulated on a TAA basis, produced lower profitability than the T4 and T6 diets that were formulated on a DAA basis. In spite of the diet formulation on a DAA basis with AA of low digestibility being more expensive due to a higher supplementation of synthetic AA, it promoted higher profitability. Rostagno et al. [4] found an increase of US$3/ton in the diet cost when formulating on DAA basis. However, the production cost of 1 kg of body weight, 1 kg of carcass weight, or 1 kg of breast meat was lower than the cost generated with the formulation based on TAA. As in the results obtained in experiment 1, supplementation with L-threonine did not influence broiler performance as compared with T1, T3, and T4 (contrast 3). It also did not significantly change CARCY, BY, DBY, AF, moisture, or CF. However, there was a significant (P < 0.05) increase in CP promoted by T2, T5, and T6 with a Thr:Lys ratio of 70:100 as compared with T1, T3, and T4, which contained lower Thr levels. It is interesting to highlight that diets formulated on DAA levels (T4 and T6), containing not only higher Thr levels but also higher SAA levels as compared with diets formulated on a TAA basis (T3 and T5) did not change CP levels. Due to these observations, it is difficult to interpret the increase in CP caused by the increase of Thr level in relation to Lys level. The supplementation of T2, T5, and T6 with L-Thr to maintain digestible the Thr:Lys ratio at 70:100 did not significantly change BEI as compared with T1, T3, and T4. Taking into consideration that there was no improvement in performance due to the maintenance of an optimum ratio between Thr and Lys levels, the lack of an increase in the BEI was also expected. CONCLUSIONS AND APPLICATIONS 1. Diet formulation with reduced CP level results in acceptable performance. Under these conditions, formulations based on DAA balance promote better weight gain than those based on TAA levels. 2. The reduction of the protein level in diets supplemented with synthetic AA increases carcass fat and decreases bone in breast meat yield. 3. The use of lower AA digestibility ingredients requires formulation based on DAA to obtain performances closer to those achieved with diets based on corn-soybean meal. 4. Formulation based on DAA promotes higher profitability for broiler production. 5. There is an indication that Thr supplementation to maintain a Thr:Lys ratio of 70:100 may promote leaner carcasses. Nevertheless, it should be the subject of additional studies to gather more evidence. REFERENCES AND NOTES 1. Smith, R. E. 1968. Assessment of the availability of amino acids in fish meal, soybean meal and feather meal by chick growth assay. Poult. Sci. 47:1624 1630. 2. Elwell, D., and J. K. Soares Jr. 1975. Amino acid availability: a comparative evaluation of several assay techniques. Poult. Sci. 54:78 85. 3. Fernández, R. S., Y. Zhang, and C. M. Parsons. 1995. Dietary formulation with cottonseed meal on a total amino acid versus a digestible amino acid basis. Poult. Sci. 74:1168 1179. 4. Rostagno, H. S., J. M. R. Pupa, and M. Pack. 1995. Diet formulation for broilers based on total versus digestible amino acids. J. Appl. Poult. Res. 4:1 7. 5. Baker, D. H., and T. K. Chung. 1992. Ideal protein for swine and poultry. Pages 1 16 in Biokyowa Technical Review 4. Biokyowa Publ. Co., Chesterfield, MO. 6. Baker, D. H., and Y. Han. 1994. Ideal amino acid profile for chicks during the first three weeks posthatching. Poult. Sci. 73:1441 1447.

DARI ET AL.: FEED FORMULATION FOR BROILERS 203 7. National Research Council. 1994. Nutrient Requirements of Poultry. 9th ed. National Academy Press. Washington, DC. 8. Heartland Lysine, Inc. 1995. True digestibility of essential amino acids for poultry. Heartland Lysine Inc., Chicago. 9. Guidoni, A. L., C. R. de M. Godoi, and C. Bellaver. 1994. Uso do Índice Nutricional Bio-Econômico como medida do desempenho nutricional animal. Page 32 in Anais da XXXI Reunião Anual da Sociedade Brasileira de Zootecnia, Maringá. ed. SBZ, Viçosa, Brazil. 10. Association of Official Analytical Chemists. 1975. Official Methods of Analysis. 12th ed. AOAC, Washington, DC. 11. Han, Y., H. Suzuky, C. M. Parsons, and D. H. Baker. 1992. Amino acid fortification of a low-protein corn and soybean meal diets for chicks. Poult. Sci. 71:1168 1178. 12. Moran, E. T., Jr., R. D. Bushong, and S. F. Bilgili. 1992. Reducing dietary crude protein for broilers while satisfying amino acid requirement by least-cost formulation: Live performence, litter composition and yield of fast-food carcass cuts at six weeks. Poult. Sci. 71:1687 1694. 13. Reginatto, M. F. 1996. Efeito da redução dos níveis de proteína bruta das dietas sobre o desempenho e a composição da carcaça de frangos de corte. Dissertação de Mestrado em Zootecnia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil. 14. Morris, T. R., I. Al-Azzawi, R. M. Gous, and G. L. Simpson. 1987. Effects of protein concentration on responses to dietary lysine by chicks. Br. Poult. Sci. 28:185 195. 15. Mendonça, C. X., and L. S. Jensen. 1989. Influence of protein concentration on the sulphur-containing amino acid requirement of broiler chickens. Br. Poult. Sci. 30:889 898. 16. Griffiths, L., S. Lesson, and J. D. Summers. 1977. Fat deposition in broilers: Effect of dietary energy to protein balance, and early life caloric restriction on productive performance and abdominal fat pad size. Poult. Sci. 56:638 646. 17. Bartov, I. 1979. Nutritional factors affecting quantity and quality of carcass fat in chickens. Fed. Proc. 38:2627 2639. 18. Pesti, G. M. 1982. Characterisation of the response of male broiler chickens to diets of various protein and energy contents. Br. Poult. Sci. 23:527 537.