Marginality and Needs of Dietary Valine for Broilers Fed Certain All-Vegetable Diets 1

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1 2007 Poultry Science Association, Inc. Marginality and Needs of Dietary Valine for Broilers Fed Certain All-Vegetable Diets 1 A. Corzo,* 2 M. T. Kidd,* W. A. Dozier III, and S. L. Vieira *Department of Poultry Science, Mississippi State University, Mississippi State 39762; USDA, Agricultural Research Service, Mississippi State, MS 39762; and Department of Animal Science, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil Primary Audience: Nutritionists, Feed Formulators SUMMARY Valine is likely the fourth limiting amino acid in most diets based on corn and soybean meal (C/SBM). However, the exact needs for Val are not well known, and information regarding it is sparse. A series of studies was conducted to validate the limitation of Val in all-vegetable diets fed to broilers, and subsequently to quantify an adequate ratio to Lys in high-yield late-developing broilers (Ross Ross 708) from 21 to 42 d. A preliminary study was designed to evaluate the supplementation of different amino acids likely to be fourth limiting on a C/SBM-based diet, where Lys, TSAA, and Thr were supplemented but no other critical amino acids were given minimums in the formulation. Results obtained for BW gain, abdominal fat weight, and abdominal fat percentage showed that birds were more responsive (P < 0.05) to L-Val supplementation. A followup study using a corn-peanut meal (C/PM)-based diet formulated to be deficient in Val validated (P < 0.05) a Val deficiency based on poor growth performance and resulted in an immediate return to good performance when this amino acid was supplemented. Furthermore, the C/PM diet was compared with a nutritionally similar C/SBM diet, and no difference was observed in the performance of broilers fed these diets, thus validating the ability of the C/PM-based diet to support adequate growth of these broilers. This C/PM-based diet was used to feed gradual concentrations of Val, from levels that would be considered deficient (0.59% digestible) up to adequate (0.84% digestible Val). Results indicate that a ratio of Val to Lys of 78, or a minimum dietary value of 0.74% digestible Val (0.82% total Val), should be adequate for this high-yield broiler grown from 21 to 42 d of age. Key words: breast meat yield, broiler, lysine, valine 2007 J. Appl. Poult. Res. 16: doi: /japr DESCRIPTION OF PROBLEM With the availability of Lys, Met, and Thr as feed grade amino acids ready for supplementation, constraints on dietary CP supply in broiler diets can be alleviated during times of increasing cost of soybean meal or animal protein by-products. Because L-Thr is now being accepted and used worldwide, the focus is now set on satisfying the needs of the fourth limiting amino acid 1 This is journal article number J11064 from the Mississippi Agricultural and Forestry Experiment Station, supported by MIS Use of trade names in this publication does not imply endorsement by the Mississippi Agricultural and Forestry Experiment Station or USDA-Agricultural Research Service of the products or of similar ones not mentioned. 2 Corresponding author: acorzo@poultry.msstate.edu

2 CORZO ET AL.: VALINE NEEDS OF GROWING BROILERS 547 in the diet if an adequately balanced dietary protein is to be fed. Regardless of whether that fourth limiting amino acid need is being satisfied in the formulation by a ratio to Lys (ideal protein) or as a nutrient minimum, the identity of this amino acid will depend completely on the feed ingredients that will constitute the diet. Recently, Kidd and Hackenhaar [1] created scenarios that varied in the type of feed ingredients being used, and hypothesized which would be the next limiting amino acid after Thr for each of those conditions. The authors suggested that when using corn and soybean meal (C/SBM) as the primary protein contributing ingredients in a broiler diet, Val was the fourth limiting amino acid based on their nutrient matrix values for dietary nutrients and nutrient ratio requirements [1]. The importance of maintaining adequate levels of dietary Val when reducing dietary CP, particularly in those diets based on C/SBM, has been described previously [2, 3, 4, 5, 6, 7]. When supplementing a C/SBM-based diet with Lys, Met, and Thr, dietary CP decreases, which often results in a concomitant decrease in diet cost. However, the ability of a diet to support optimal broiler performance will largely rely on maintaining adequate levels of those limiting amino acids subsequent to Thr. For that purpose, a series of studies was conducted to validate the importance of dietary Val in C/SBM-based diets and assess its need in a high-yield, late-developing broiler strain cross. MATERIALS AND METHODS Bird Husbandry For all studies, the following experimental conditions applied. Ross Ross 708 [8] 1-d-old male chicks were used. They were randomly distributed into floor pens in a closed-sided house equipped with thermostatically controlled heating, curtains, and cross-ventilation. Built-up litter was used in all pens, and pens were equipped with a nipple drinker line (3 nipples/ pen) and a hanging feeder (22.5 kg capacity). Feed and water were offered ad libitum. The lighting program consisted of 23 h of light and 1 h of dark. Ventilation was accomplished by negative air pressure. Chicks were vaccinated for Marek s disease (via in ovo administration at d 18), Newcastle disease, and infectious bronchitis (via coarse spray at hatch). From placement to 21 d of age, the birds received common C/SBM feeds formulated to meet or exceed nutrient recommendations [9], and feeds were provided in crumbled form. At 21 d of age, bird numbers were equalized among all pens (12 birds/pen; 0.1 m 2 /bird), and treatments were assigned to pens to provide a similar distribution of average bird weight at the start of the experiments. Evaluation Criteria The mean bird weight of all pens was recorded at the initiation (21 d) and termination (42 d) of the experimental phase for all experiments. Feed consumption and mortality were recorded. Feed conversion was corrected for mortality and represents grams of feed consumed by all birds in a pen divided by grams of BW gain per pen plus the BW of the birds that died. For experiments 1 and 3, 6 birds per pen were weighed at d 42 and cooped 12 h before processing. Carcass and abdominal fat weights were obtained and recorded. Carcasses were chilled for 4 h and the breast muscles (boneless-skinless) were manually deboned, weighed, and recorded. Statistical Analyses Data obtained from each experiment were evaluated by ANOVA by using a randomized complete block design. Pen was used as the experimental unit for analysis. Percentage data for mortality were transformed to arcsine square root percent for analysis. All data were analyzed by the GLM procedure of SAS [10]. Treatment effects were tested and means were separated by using a Tukey test with an α of For experiment 3, data were evaluated for linear, quadratic, or cubic responses. Only linear and quadratic effects are displayed, because significance (P > 0.05) was not observed in higher order polynomials. Regression analysis was used to estimate Val optimization (95% of the maximum response) whenever a significant quadratic response (P < 0.05) was observed. Diets and Experiments Calculated total and digestible amino acid values of feed ingredients used in all studies

3 548 JAPR: Research Report Table 1. Experimental diet composition (%, as-is) Ingredient CS-1 1 Test 2 CS-2 3 C/PM 4 Corn Soybean meal Peanut meal Poultry fat Dicalcium phosphate Limestone Salt Filler Vitamin-mineral premix DL-Met L-Lys Sacox L-Thr Choline Cl, 60% L-Ile L-Trp Calculated composition 8 CP, % ME, kcal/kg 3,100 3,100 3,125 3,125 Calcium, % Available phosphorus, % Choline, ppm 1,531 1,500 1,500 1,500 Digestibility, % Lys TSAA Thr Ile Val Arg Trp Gly + Ser Diet represents the control treatment (experiment 1). 2 Diet represents the test diet used in experiment 1; it also served as the diet by which the remaining dietary treatments were manufactured by supplementing their respective amino acids at the expense of the inert filler (sand). 3 Treatment represents the corn-soybean meal (CS)-based dietary treatment that served as a positive control (experiment 2). 4 Treatment represents the basal corn-peanut meal (C/PM)-based dietary treatment ( Val and +Val; experiment 2); the C/ PM diet also served as the diet used to titrate Val in experiment 3. 5 Filler represented inert space (sand) in the diet, to which L-Val, L-Ile, L-Arg, or Gly was added at its expense to derive the projected dietary treatments. 6 The vitamin and mineral premix contained (per kg of diet): retinyl acetate, 2,654 g; cholecalciferol, 110 g; DL-αtocopherol acetate, 9.9 mg; menadione, 0.9 mg; B 12, 0.01 mg; folic acid, 0.6 mg; choline, 379 mg; D-pantothenic acid, 8.8 mg; riboflavin, 5.0 mg; niacin, 33 mg; thiamin, 1.0 mg; D-biotin, 0.1 mg; pyridoxine, 0.9 mg; ethoxiquin, 28 mg; manganese, 55 mg; zinc, 50 mg; iron, 28 mg; copper, 4 mg; iodine, 0.5 mg; selenium, 0.1 mg; myco-lock adsorbent (0.05% of diet); and santoquin (0.02% of diet). 7 Dietary inclusion of 60 g of salinomycin sodium per kg of feed. 8 Total analyzed amino acid composition of the experimental diets. Experiment 1: CS-1 (0.72% Ile, 0.79% Val, 1.14% Arg, and 1.59% Gly + Ser); test (0.67% Ile, 0.74% Val, 1.09% Arg, and 1.56% Gly + Ser). Experiment 2: CS-2 (1.05% Lys, 0.84% TSAA, 0.73% Thr, 0.76% Ile, and 0.81% Val); C/PM (1.06% Lys, 0.84% TSAA, 0.71% Thr, 0.75% Ile, and 0.64% Val). Experiment 3: C/PM (0.66% Val). were obtained from Ajinomoto Heartland Inc. [11] (true digestibility of essential amino acids for poultry). Composite samples of dietary treatments were obtained and analyzed for protein bound and supplemented amino acids [12] to ensure that calculated and analyzed total amino acid values were in agreement. Experiment 1 was designed to measure amino acid supplementation to a diet that was formulated to meet Lys, TSAA, and Thr needs of growing broilers, but that disregarded the amino acid levels of other potential limiting amino acids (Table 1). Supple-

4 CORZO ET AL.: VALINE NEEDS OF GROWING BROILERS 549 mentation was done by adding L-Ile, L-Arg, L- Val, or Gly to a test diet at the expense of an inert filler (sand). A diet with a higher CP that ensured that all the other (Ile, Arg, Val, Gly + Ser) limiting amino acids would be supplied at adequate levels served as the control (CS-1). Diets were fed in pellet form. The 6 treatments were replicated 6 times, with each experimental unit consisting of a floor pen ( m) composed of 12 broilers. Experiment 2 was designed to validate a deficiency in dietary Val, and to observe whether L-Val supplementation would result in the return of satisfactory performance. This study was also intended to validate the use of a corn-peanut meal (C/PM)-based diet as a dose-response diet, to be used in experiment 3, by comparing it with the performance obtained by birds fed a C/SBMbased diet with similar nutritional characteristics (CS-2). Diets were fed in pellet form. A total of 3 treatments were fed, each replicated 6 times, with each experimental unit consisting of a floor pen ( m) composed of 12 broilers. The final study (experiment 3) attempted to estimate the optimal Val-to-Lys ratio of broilers fed a dose-response diet deficient in dietary Val (0.59% digestible Val), consisting of 6 different graded levels of dietary Val accomplished by the addition of L-Val at 0.05% of the diet at the expense of an inert filler (sand). The doseresponse diet was a C/PM-based diet fed in pellet form and formulated to minimize Val content while ensuring the minimal levels of all other essential amino acids in a manner that would meet or exceed current recommendations [9]. However, dietary Lys was formulated to be slightly marginal (0.95% digestible) so that an overestimation of the Val-to-Lys ratio would not occur. A total of 6 progressive dietary Val levels were replicated 8 times, with each experimental unit consisting of a floor pen ( m) composed of 12 broilers. All animal procedures were approved by the university s Institutional Animal Care and Use Committee. RESULTS AND DISCUSSION Experiment 1: Marginality of Val in C/SBM-Based Diets Total amino acid analyses of the experimental diets showed that the test diet had marginal dietary Ile, Val, Arg, and Gly + Ser levels compared with those observed in the control diet (Table 1, footnote 8). The reduction in CP can lead to other amino acids becoming limiting when those are not considered during formulation. The effects of feeding a high-cp diet, a low-cp diet (test) supplemented with Lys, Met, and Thr but with limiting levels of other potential amino acids, and their subsequent individual additions to that low-cp test diet are displayed in Table 2. It should be noted that only those parameters that resulted in a significant treatment effect during experiment 1 are displayed. A depression in growth and feed conversion concurrent with an increase in abdominal fat absolute and relative weights was the result of feeding the test diet when compared with the control and some of the other dietary treatments. These data illustrate that amino acid minima or ratios should be used during formulation to prevent depression of growth and feed conversion when feeding a reduced dietary CP in an attempt to decrease cost, nitrogen excretion, or both. Interestingly, only the addition of dietary Val resulted in broilers with BW gain, abdominal fat weight, and abdominal fat percentage similar to those fed the control diet (Table 2). Even though those broilers supplemented with L-Val failed to separate themselves statistically from most of the other supplemented amino acids, it was the only dietary treatment that resulted in intermediate responses that were similar to those seen in broilers fed the control diet. Even though data suggest that a nitrogen response may have been observed for most of the supplemented amino acids used in this study, it was only Val supplementation that statistically equaled the control group, indicating that, perhaps more than a nitrogen response, a dietary limitation likely occurred. The composite of responses elucidates the importance of Val as a potential fourth limiting amino acid in C/SBMbased diets, particularly when a reduction in CP takes place. Similar observations have been reported previously [2, 5], in agreement with the limitation for Val when feeding C/SBM-based diets. Values and responses very similar to those reported here for abdominal fat percentage were previously documented [3]. This similarity in abdominal fat percentage between the control diet and the test Val-supplemented diet can be

5 550 JAPR: Research Report Table 2. Live performance and abdominal fat percentage of broiler chickens fed supplemental dietary levels of Val, Ile, Arg, or Gly (experiment 1) 1 Abdominal fat Treatment 2 BW gain, g FCR 3 Weight, g Percentage CS-1 1,662 a 1.88 c 31 c 1.88 d Test 1,462 c 2.18 a 37 ab 2.51 ab Test + Val 1,593 ab 2.05 b 34 bc 2.17 cd Test + Ile 1,567 b 2.03 b 39 ab 2.52 ab Test + Arg 1,537 bc 2.02 b 40 a 2.65 a Test + Gly 1,493 c 2.03 b 37 ab 2.39 abc SEM P a d Values with a different superscript within each column differ (P 0.05). 1 Values are the observed means of 6 replicate units per treatment mean. 2 Treatments: CS-1 diet (20% CP, 0.81% digestible Val, 0.73% digestible Ile, 1.15% digestible Arg, and 1.69% total Gly + Ser); test diet (17.5% CP, 0.69% digestible Val, 0.62% digestible Ile, 0.98% digestible Arg, and 1.44% total Gly + Ser); test diet % L-Val = 0.79% digestible Val; test diet % L-Ile = 0.72% digestible Ile; test diet % L-Arg = 1.08% digestible Arg; test diet % Gly = 1.54% Gly + Ser. 3 Values represent the feed conversion values after being corrected for mortality. partially explained by the unique ability of this amino acid to reduce certain lipogenic pathways [13]. Experiment 2: Val Deficiency and Dose- Response Diet Validation The diets used for the second study were a C/SBM-based diet and a nutritionally similar diet based on C/PM. The C/PM diet was formulated to validate a nutritional deficiency of Val. As expected, total dietary Val values differed when comparing the experimental diets used in this second study (Table 1). One can observe how the nutrient composition of the CS-2 diet and the C/PM diet differed only in their dietary Val levels (Table 1, footnote 8). Table 3 shows how growth, in the form of BW gain and feed conversion, was impaired by the C/PM Val-deficient diet. Data in Table 3 also demonstrate how the Val deficiency was overcome in this same C/PM diet with L-Val supplementation at the expense of an inert filler. The Val deficiency, and its subsequent correction via L-Val supplementation, was further demonstrated when comparing those responses against the growth obtained by broilers fed a nutritionally similar CS- 2-based diet. Equally as important as validating a Val deficiency with the use of this C/PM-based diet was the fact that L-Val supplementation corrected this deficiency, as judged by comparison with the CS-2-based diet. The similar responses observed between the broilers fed the CS-2 diet and those fed the nutritionally Val-adequate C/ PM diet validate the ability of the latter to sup- Table 3. Live performance of broiler chickens fed basal and supplemental dietary levels of Val (experiment 2) 1 Treatment 2 BW gain, g Feed intake, g FCR 3 CS-2 1,570 ab 3, ab C/PM Val 1,480 b 2, a C/PM + Val 1,611 a 3, b SEM P a,b Values with a different superscript within each column differ (P 0.05). 1 Values are the observed means of 6 replicate units per treatment mean. 2 Treatments: corn-soybean meal (CS-2)-based diet (0.74% digestible Val and 0.95% digestible Lys); corn-peanut meal (C/ PM)-based diet Val (0.59% digestible Val and 0.95% digestible Lys); C/PM-based diet + Val (0.74% digestible Val and 0.95% digestible Lys). 3 Values represent the feed conversion values after being corrected for mortality.

6 CORZO ET AL.: VALINE NEEDS OF GROWING BROILERS 551 port adequate growth and feed efficiency. Furthermore, this diet allowed for an estimation of dietary Val needs via the dose-response methodology as in experiment 3. The ability of a C/ PM-based diet to support satisfactory growth when compared with more conventional diets is in agreement with previous work that used a C/PM-based diet during Thr-based studies in broilers [14]. For that purpose, experiment 3 used this C/PM diet as a way to estimate the Val needs of broilers as a proportion of dietary Lys. Experiment 3: Val Needs Relative to Lys The third study was designed to extrapolate a dietary Val value expressed relative to Lys, therefore expressing its requirement by using the ideal protein concept. Because of the lack of data regarding Val nutritional needs and the fact that its nutritional adequacy is always met by the inclusion of proteinaceous feed ingredients such as soybean meal, it was the objective of this study to obtain such a ratio, foreseeing its practicality and applicability in the industry. For that purpose, the C/PM-based diet formulated to obtain this ratio was set to meet or exceed nutrient recommendations [9] for all limiting amino acids involved, except for Val. Actual total Val analysis of the experimental basal diet showed that the C/PM diet used for titration was deficient in dietary Val (0.66% total Val; Table 1). The calculated digestible Val value (0.59%) matches the reported total Val value of the experimental C/PM diet. Results for BW gain showed how a quadratic response was observed with dietary Val (Table 4). Regression analysis revealed that a Val-to- Lys ratio of 78 was optimal for maximizing BW gain under these experimental conditions (Table 5). Baker et al. [15] reported a similar Val-to- Lys ratio (77.5), using BW gain and feed efficiency as evaluation criteria. However, it should be noted that Baker et al. used a different broiler strain cross and estimated this ratio at a younger age. Mack et al. [16] fed graded levels of Val, among other amino acids, and estimated an ideal ratio of Val to Lys of 81. Although the work by Mack et al. closely resembled the age used during our experiment, the bird strain used did not, and that may explain the slight difference in ratio. Feed conversion was improved and displayed a linear effect with increasing Val supplementation (Table 4). As expected, increased dietary Val supplementation led to a linear effect for Val intake. No effect derived from dietary Val status was observed for the incidence of mortality. After processing the broilers, a linear increase with Val supplementation was observed for carcass weight, but not yield (Table 6). Perhaps this effect closely reflects the response observed for BW gain. In contrast to the abdominal fat responses observed in the first study, no effect was observed for abdominal fat weight or percentage caused by dietary Val (Table 6). Removal of breast muscles showed numerous effects attributable to dietary Val (Table 7). Quadratic effects for both types of pectoral muscles (fillets: pectoralis major; tenders: pectoralis minor) and their composite were seen. Yield values displayed significant quadratic responses for fillets, tenders, and breast meat yield only when proportionate to carcass weight. Total breast meat yield value expressed relative to the live BW reached borderline significance (P = 0.07), and its quadratic response yielded a Val optimization ratio to Lys similar to that seen when expressed relative to the carcass weight. The absolute weight of these muscles and their composite was maximized with Val-to-Lys ratios between 76 and 77, whereas their yield was optimized between 72 and 74 (Table 5). A similar effect was observed previously [16], in which Val was optimized with a lower amount for breast meat yield compared with BW gain and feed conversion. Furthermore, the resultant Valto-Lys ratio of Mack et al. [14] was considerably less for breast meat yield because they reported a higher need for Lys for optimization of breast meat yield. This is not unusual because of the demanding role of Lys in protein accretion and maintenance in the breast muscle of chickens [17, 18]. Thus, the Lys roles for maintenance change considerably when comparing growth vs. breast meat, but the Val maintenance need for breast meat tissue did not appear to increase proportionally to the Lys needs, perhaps explaining why the resultant Val-to-Lys ratios were lower when considering breast meat yield as the evaluation criterion. It can be concluded that Val is likely the fourth limiting amino acid in C/SBM-based diets, and particular attention should be given to the resultant dietary Val level when at-

7 552 JAPR: Research Report Table 4. Live performance of broilers fed diets with various levels of dietary Val (experiment 3) 1 Val intake, Dietary Val, 2 % BW gain 3 FCR 4 g/bird Mortality, % SEM Probability Val linear Val quadratic Values are the observed means of 8 replicate units per treatment mean. 2 Treatments are expressed on a digestible basis. 3 Values represent the BW gain per bird, expressed in kg. 4 Values represent the feed conversion values after being corrected for mortality. Table 5. Quadratic regression equations of measurements having significant quadratic response by broiler males after receiving progressive dietary levels of Val Maximum Response criterion Equation 1 response 2 Val:Lys BW gain, kg y = (Val) (Val) Fillet weight, kg y = (Val) (Val) Tender weight, kg y = (Val) (Val) Total breast weight, kg y = (Val) (Val) Fillet yield, % y = (Val) (Val) Tender yield, % y = (Val) (Val) Total breast meat yield, % y = (Val) (Val) Prediction equation based on total dietary Val. 2 Digestible dietary Val requirement estimates are 95% of the maximum response. Table 6. Carcass and abdominal fat weights of broilers fed diets with various levels of dietary Val 1 Carcass Abdominal fat Dietary Val % 2 Weight, kg Yield, 3 % Weight, g Amount, 4 % SEM Probability Val linear Val quadratic Values are the observed means of 8 replicate units per treatment mean. 2 Treatments are expressed on a digestible basis. 3 Values are expressed as the carcass weight relative to the full-fed live BW. 4 Values are expressed as the abdominal fat weight relative to the full-fed live BW.

8 CORZO ET AL.: VALINE NEEDS OF GROWING BROILERS 553 Table 7. Breast meat weights of broilers fed diets with various levels of dietary Val 1 Fillet Tender Total breast meat Dietary Val, 2 % Weight, g Yield, % Weight, g Yield, % Weight, g Yield, 3 % Yield, 4 % SEM Probability Val linear Val quadratic Values are the observed means of 8 replicate units per treatment mean. 2 Treatments are expressed on a digestible basis. 3 Values are expressed as the total breast meat weight relative to the carcass. 4 Values are expressed as the total breast meat weight relative to the full-fed live BW. tempting to reduce CP. Furthermore, Val needs may be of greater relevance in certain regions of the world where the use of animal by-products in the manufacture of poultry feeds is prohibited. We demonstrated that if a certain dietary Val level is not considered in the formulation, the efficiency of a diet could lead to a decrease in production. A Val-to-Lys ratio of 78 (0.74% digestible Val; 0.82% total Val) is recommended for this broiler strain under this time frame, closely agreeing with the recommendations by Baker et al. [15]. CONCLUSIONS AND APPLICATIONS 1. Dietary Val is the likely fourth limiting amino acid in C/SBM-based diets and C/PM-based diets. 2. Based on the present results, the Val-to-Lys recommendation is 78 (0.74% digestible Val; 0.82% total Val) for high-yielding Ross Ross 708 male broilers from 21 to 42 d of age. REFERENCES AND NOTES 1. Kidd, M. T. and L. Hackenhaar Dietary threonine for broilers: Dietary interactions and feed additive supplement use. CAB Rev. 1. No Edmonds, M. S., C. M. Parsons, and D. H. Baker Limiting amino acids in low-protein corn-soybean meal diets fed to growing chicks. Poult. Sci. 64: Mendoca, C. X., and L. S. Jensen Influence of valine level on performance of older broilers fed low protein diet supplemented with amino acids. Nutr. Rep. Int. 40: Han, Y., H. Suzuki, C. M. Parsons, and D. H. Baker Amino acid fortification of a low protein corn-soybean meal diet for maximal weight gain and feed efficiency of the chick. Poult. Sci. 71: Fernandez, S. R., S. Aoyagi, Y. Han, C. M. Parsons, and D. H. Baker Limiting order of amino acids in corn and soybean meal for growth of the chick. Poult. Sci. 73: Corzo, A., E. T. Moran Jr., and D. Hoehler Valine needs of male broilers from 42 to 56 days of age. Poult. Sci. 83: Thronton, S. A., A. Corzo, G. T. Pharr, W. A. Dozier III, D. M. Miles, and M. T. Kidd Valine requirements for immune and growth responses in broilers from 3 to 6 weeks of age. Br. Poult. Sci. 47: Aviagen Inc., Huntsville, AL. 9. NRC Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 10. SAS Institute SAS Proprietary Software, Release 8.1. SAS Inst. Inc., Cary, NC. 11. Ajinomoto Heartland Inc., Chicago, IL. 12. Llames, C. R., and J. Fontaine Determination of amino acids in feeds. Collaborative Study. J. AOAC Int. 77: Taylor, W. M., and M. L. Halperin Effect of valine on the control of fatty acid synthesis in white adipose tissue of the rat. Can. J. Biochem. 53: Kidd, M. T., S. P. Lerner, J. P. Allard, S. K. Rao, and J. T. Halley Threonine needs of finishing broilers: Growth, carcass, and economic responses. J. Appl. Poult. Res. 8: Baker, D. H., A. B. Batal, T. M. Parr, N. S. Augspurger, and C. M. Parsons Ideal ratio (relative to lysine) of tryptophan,

9 554 JAPR: Research Report threonine, isoleucine, and valine for chicks during the second and third weeks posthatch. Poult. Sci. 81: Mack, S., D. Bercovici, G. DeGroote, B. Leclercq, M. Lippens, M. Pack, J. B. Schutte, and S. Van Cauwenberghe Ideal amino acid profile and dietary lysine specification for broiler chickens of 20 to 40 days of age. Br. Poult. Sci. 40: Tesseraud, S., M. Larbier, A. M. Chagneau, and P. A. Geraert Effect of dietary lysine on muscle protein turnover in growing chickens. Reprod. Nutr. Dev. 32: Tesseraud, S., S. Temim, E. Le Bihan-Duval, and A. M. Chagneau Increased responsiveness to dietary lysine deficiency of pectoralis major muscle protein turnover in broilers selected on breast development. J. Anim. Sci. 79: