Lysine and Arginine Requirements of Broiler Chickens at Twoto Three-Week Intervals to Eight Weeks of Age

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1 Lysine and Arginine Requirements of Broiler Chickens at Twoto Three-Week Intervals to Eight Weeks of Age M. C. Labadan, Jr., 1 K.-N. Hsu, and R. E. Austic 2 Department of Animal Science, Cornell University, Ithaca, New York ABSTRACT Four experiments were conducted to determine minor) were not significantly higher than those from body the arginine and lysine requirements of male chickens for 2- to 3-wk intervals from the time of hatching weight gain. However, they tended to be higher than for feed efficiency for 0-to-2 and 2-to-4-wk-old broilers. until 8 wk of age. Weight gain, breast muscle growth, and Lysine and arginine requirements, as percentages of total feed efficiency were used as response for each interval. amino acid in the diet, for maximum breast muscle Dietary requirements for lysine and arginine were estimated by broken-line regression analysis of responses to growth were, respectively, 1.32 ± 0.01% and 1.27 ± 0.00% to 2 wk of age, 1.21 ± 0.06% and ND for 2 to 4 wk of age, 0.99 ± 0.02% and 0.97 ± 0.02% for 3 to 6 wk of age, and 0.81 six or seven dietary levels of each amino acid. Dietary ± 0.01% and 0.83 ± 0.02% for 5 to 8 wk of age. Calculated crude protein levels were 22, 21, 20, and 18% in four digestible lysine and arginine requirements were, respectively, 1.24 and 1.19% to 2 wk of age, 1.11% and ND for consecutive experiments from 0 to 2, 2 to 4, 3 to 6, and 5 to 8 wk of age. An occasional estimate of requirement 2 to 4 wk of age, 0.92% and 0.91% for 3 to 6 wk of age, was not determined (ND) because the response did not and 0.75 and 0.78% for 5 to 8 wk of age. The requirements conform to the regression model. The values for lysine and arginine requirements determined from breast muscle gain (weight gain of pectoralis major plus pectoralis for lysine and arginine were similar except for the earliest age group for which the lysine requirement appeared to be slightly higher than that of arginine. (Key words: body weight, feed efficiency, breast muscle, yield, broiler) 2001 Poultry Science 80: INTRODUCTION Several studies have been carried out to determine the lysine requirements of modern fast-growing broiler chickens. Modern statistical methods have been applied in most of these to obtain estimates of the requirement based on growth rate, feed efficiency, and other measures. Recent studies of Morris et al. (1987), Morris and Abebe (1990), and Surisdiarto and Farrell (1991) confirmed the positive relationships of the lysine requirement to dietary protein level, as had been indicated in the early research of Grau and Kamei (1950). Their studies demonstrated the linearity of the relationship between lysine requirement and dietary protein level and support the view that the lysine requirement of 3-wk-old broilers fed a diet containing 23% CP ranges from 1.26 to 1.33% for maximum weight gain and feed efficiency. However, Han and Baker (1991) studied fast- and slow-growing broiler chicks fed a diet containing 23% CP and found the requirement of 8- to 21-d old chicks 2001 Poultry Science Association, Inc. Received for publication March 13, Accepted for publication December 18, Present address: MML DC Building, Celery Road, FTI Complex, Taguig, Metro Manila, Philippines. 2 To whom correspondence should be addressed: rea2@cornell.edu. to be not greater than 1.17% (1.01% digestible) lysine for maximal weight gain and 1.41% (1.21% digestible) lysine for maximal feed efficiency for both strains. These estimates of requirement are substantially higher than the 1.10% of the diet estimated by the National Research Council (NRC, 1994) for broilers to 3 wk of age fed a diet containing 23% CP. Han and Baker (1994) studied the lysine requirement of both sexes during the period from 3 to 6 wk of age. The requirement for lysine in a diet containing 20% CP for maximum weight gain was 0.99% for males and 0.91% for females; the requirement for optimum feed efficiency for males was 1.03% and for females is 0.99% lysine in the diet. The authors concluded that the requirement for maximum breast meat yield was not significantly different from requirement for maximum feed efficiency. These lysine requirement values are similar to those of the NRC (1994) that estimated the lysine requirement for 3- to 6-wk old broilers at 1.00% of a 20% CP diet and the lysine requirement for 6- to 8-wk old broilers at 0.85% of an 18% CP diet. Several studies on breast meat yield suggest that lysine requirements of broilers are higher than indicated by NRC (1984, 1994). Hickling et al. (1990) compared the lysine requirement (1.20% starter and 1.00% grower) estimated by the NRC (1984) and 106, 112, and 118% of the NRC level at 100 and 112% of the NRC (1984) methionine level 599

2 600 LABADAN ET AL. TABLE 1. Experimental design 1 Dietary crude Dietary lysine Dietary arginine Experiment no. Period protein (%) (%) (%) wks wks wks wks Six equally spaced dietary levels of each amino acid were used for all the experiments except for Experiment 1, which had seven dietary levels. for broilers to 6 wk of age. There were no responses in body weight and feed efficiency to 6 wk, but increasing lysine levels at the higher dietary methionine level produced a cubic regression response in breast meat yield (P < 0.05), with yield increasing as lysine increased to 112% of the NRC (1984) (1.34% of the starter diet; 1.18% of the grower diet). Moran and Bilgili (1990) reported that 0.85% total lysine was inadequate for broilers 28 to 42 d old. Supplementation of L-lysine HCl to provide 0.95 and 1.05% total lysine did not increase body weight but improved feed conversion and increased breast muscle yield. Acar et al. (1991) conducted experiments on lysine requirement of 6- to 8-wk-old broilers of two different male broiler strains. Neither strain responded in growth, feed efficiency, or breast meat yield to dietary levels from 0.75 to 1.15% total lysine in the diet. However, a strain lysine interaction was observed for breast weight. Bilgili et al. (1992) suggested that the lysine requirement during the finisher period (6 to 8 wk) for optimum breast muscle yield may be higher than the 0.85% estimated by the NRC (1984). Similar evidence of an increased lysine requirement above NRC (1994) estimated requirements after 3 wk of age was provided by Renden et al. (1994). Holsheimer and Ruesink (1993) reported that higher than 1.15% dietary lysine in the starter period (to 14 d of age) resulted in higher breast muscle yield at 49 d of age, irrespective of dietary lysine level in the range of 1.10 to 1.30% from 15 to 49 d of age. Summers et al. (1988) observed no difference in breast muscle yield in their study of 6-wk-old broilers when a diet with 17% CP and containing 0.88% lysine was supplemented with 0.32% lysine. There have been a few studies of the arginine requirements of modern commercial broilers. Burton and Waldroup (1979) reported an arginine requirement of 1.40% for chicks from 1 to 28 d old that were fed a diet containing 21% CP. This study, however, showed no significant difference in 4-wk body weights and feed to gain ratios of chicks fed 1.25 and 1.40% arginine in the diet. Based on their statistical analysis, the requirement of 1.40% does not seem to be justified. Cuca and Jensen (1990) estimated the arginine requirements for growth to be from 1.10 to 1.28% of the diet and for maximum feed efficiency from 0.96 to 1.28% of the diet. Kessler and Thomas (1976) used growth and feed efficiency as well as feather loss to estimate the requirements of 4- to 7-wk-old broilers. They found the 3 ConAgra, Inc., Seaford, DE arginine requirement of male broilers to be 1.13% arginine in the diet. The National Research Council estimated the arginine requirement of broilers to be 1.25% of the diet to 3 wk, 1.10% from 3 to 6 wk, and 1.00% from 6 to 8 wk of age (NRC, 1994). The present study was conducted to determine, in experiments carried out simultaneously with similar diets, the lysine and arginine requirements of broilers from 0 to 8 wk. It was designed to determine the relative lysine and arginine requirements of broilers at different ages and to utilize breast muscle growth as a measure of performance. MATERIALS AND METHODS General Procedures All experiments were conducted with male (Ross male Avian female) commercial broiler chicks 3 that were maintained in Petersime battery brooders with raised wire floors, feed troughs, and trough waterers. Prior to each experiment, the broilers were grouped by weight and randomly distributed to pens in such a way as to reduce variation in mean chick weights per pen. A completely randomized design was utilized in all the experiments. Feed and water were given ad libitum, and 23 h daily lighting was provided. The temperature inside the brooders was 35 C and was decreased weekly by 2.5 C until the third week, when a temperature around 22 C was maintained. After the second week, the birds were transferred to three-tier Petersime battery finishing cages with raised wire floors, feed trough, and nipple-type drinkers. Four experiments were conducted, one each for broilers from 0 to 2, 2 to 4, 3 to 6, and 5 to 8 wk of age. Arginine and lysine experiments were done simultaneously for each 2-to-3-wk interval. The trials consisted of the treatments shown in Table 1. Quadruplicate samples of each basal diet were hydrolyzed by heating samples for 24 h in sealed tubes with 6 N HCl. Amino acids were then analyzed by ion-exchange chromatography. Chromatography was done with an HPLC, using o-phthalaldehyde derivatization, fluorescence detection, and an automatic peak integration system. Protocols for all experiments were approved by the Cornell University Institutional Animal Care and Use Committee. Experiment 1 This experiment was conducted to determine the lysine and arginine requirements broiler chicks to two wk of

3 LYSINE AND ARGININE REQUIREMENTS 601 age. Two basal diets (Table 2) composed of practical and purified ingredients were formulated to satisfy the amino acid requirements according to NRC (1994) estimates of requirements, except for the levels of lysine and arginine, which were expected to be limiting. The diets were similar except for the reduction in casein and increases in other protein sources in the second basal diet to make it lysine limiting. Lysine and arginine were supplemented as L- lysine HCl and L-arginine (free base), respectively, in all experiments. There were seven dietary treatments each for lysine and arginine. Each treatment had four replicates of four chicks. Chicks were received by mail 2 d after hatching. Their initial body weights averaged 33 g. Experiment 2 This experiment was conducted to determine the lysine and arginine requirements of 2- to 4-wk-old broilers. As in Experiment 1, two basal diets (Table 2) limiting in lysine or arginine were formulated to satisfy the other essential amino acids according to NRC (1994) estimates of requirements. There were six dietary treatments each for the lysine and arginine series. Each treatment had four replicates of four chicks. Chicks were 15 d old at the beginning of the experiment, and their initial mean body weights were 408 g. Prior to this experiment, the chicks were fed a 22% CP practical diet that would satisfy their nutritional requirements according to the NRC (1994), except for lysine, which was based on NRC (1984). Experiment 3 The lysine and arginine requirements of 3- to 6-wk-old broilers were determined in this experiment. Unlike the previous experiments, a single basal diet (Table 2) was formulated to be deficient in lysine and arginine but ade- TABLE 2. Composition of basal diets (%) Experiment 1 Experiment 2 Experiment 3 Experiment 4 Ingredients 22% CP 22% CP 21% CP 21% CP 20% CP 18% CP Corn, ground Corn gluten meal Soybean meal (48% CP) Menhaden meal (60% CP) Cerelose Cellulose Peanut meal Casein Corn oil Vitamin premix Mineral premix L-Lysine HCl DL-Methionine L-Arginine L-Threonine L-Tryptophan L-Isoleucine L-Valine Calculated composition M.E. Kcal/kg 3,200 3,200 3,200 3,200 3,200 3,200 Arginine, % Arginine, % (digestible) Glycine, % Serine, % Histidine, % Isoleucine, % Leucine, % Lysine, % Lysine, % (digestible) Methionine, % Cystine, % Phenylalanine, % Tyrosine, % Threonine, % Tryptophan, % Valine, % Analyzed composition Arginine, % Lysine, % Vitamin premix provides per kilogram of diet: vitamin A, 4,500 IU; vitamin D 3, 2,250 ICU; vitamin E, 50 IU; thiamin HCl, 15 mg; riboflavin, 15 mg; nicotinic acid, 50 mg; folic acid, 6 mg; pyridoxine, 6 mg; biotin, 0.6 mg; vitamin B 12, 0.02 mg; choline Cl, 2,500 mg; d-calcium pantothenate, 20 mg; menadione sodium bisulfite, 1.5 mg; butylated hydroxytoluene, 100 mg; glucose to make 12 g. 2 Mineral premix provides per kilogram of diet: CaCO 3, 25.6 g; CaHPO 4 2H 2 O, 5.6 g; KH 2 PO 4, 14 g; NaCl, 5.1 g; MnSO 4 H 2 O, 0.33 g; FeSO 4 7H 2 O, 0.33 g; KI, g; CuSO 4 5H 2 O, 0.05 g; ZnO, 0.1 g; CoCl 2 6H 2 O, g; NaMoO 4 2H 2 O, g; Na 2 SeO 3, g.

4 602 LABADAN ET AL. TABLE 3. Response of 0- to 2-wk-old broilers to arginine and lysine (Experiment 1) Arginine Lysine Weight Breast Feed Dietary Weight Breast Feed Dietary gain muscle intake Gain:feed lysine gain muscle intake Gain:feed 1 arginine (%) (g) (g) (g) (g:g) (%) (g) (g) (g) (g:g) Pooled SEM Arginine 1.24 ± ± 0.00 ND ± 0.04 Lysine 1.28 ± ± 0.01 ND 1.21 ± 0.02 requirement 2 requirement 2 1 Mean of four replicates of four chicks from 2 to 24 d; mean initial body weight was 33 g per chick. 2 Requirement ± SE based on broken-line regression analysis. 3 Not determined. quate in all other essential amino acids according to NRC (1994) estimates of requirements. The diets in the lysine series were supplemented with L-arginine to provide 1.15% arginine in all the diets. The diets in the arginine series were supplemented with L-lysine HCl to provide 1.15% lysine in all the diets. Six dietary treatments each for lysine and arginine were randomly allocated with four replicates of four chicks. The chicks were 22 d old at the beginning of the experiment, and the starting weight of the broilers was 870 g. Chicks were fed practical diets, with 22% CP for 2 wk and then a 21% CP diet during the third week. Both diets were formulated to satisfy the nutritional requirements as estimated by the NRC (1994) except lysine, which was based on NRC (1984). Experiment 4 An 18% CP basal diet (Table 2) was formulated for the determination of the lysine and arginine requirements of 5- to 8-wk-old broilers. The diets in the lysine series were supplemented with L-arginine to provide 1.05% arginine in all the diets. The diets in the arginine series were supplemented with L-lysine HCl to provide 1.05% lysine in all the diets. Six dietary levels each for lysine and arginine were randomly allocated with four replicates of four birds. The broilers were 36 d old at the start of this experiment, and the average initial weight of the birds was 1,675 g. Chicks were fed a practical 22% CP diet for the first 2 wk, then a 20% CP diet prior to the experiment. Both diets were formulated to satisfy the nutritional requirements according to the NRC (1994) except for lysine, which was based on NRC (1984). Measured Variables Body Weight Gain, Feed Consumption, and Feed Efficiency. The initial weights of the birds were taken at the 4 Minitab Inc., State College, PA SAS Institute, Inc., Cary, NC start of each experiment. At the end of all the experiments, final weights of the broilers were recorded, and initial weights were subtracted from the final weights to obtain weight gain. Feed consumption was measured, corrected when necessary for mortality, and the feed efficiency (g gain/g feed) was calculated. Breast Muscle Growth. In Experiments 1 through 3, birds were euthanized by CO 2 asphyxiation. Four people per replicate were trained to perform the removal of breast muscle. Special care was taken to reduce variation and maintain consistency among the four individuals. Each individual prepared breast muscle from one chick per replicate. The skin was removed from the breast area, and the left breast muscle (pectoralis major and pectoralis minor muscles) was then excised and stripped from the carcass, pooled by pen, and then weighed. In Experiment 4, legbanded birds were transferred to the slaughter facility at the Poultry Research Farm. After slaughter, bleedout, defeathering, and evisceration, the carcasses were split in half. The breast muscle on the left side of the carcass was then excised and stripped from the carcass. The broilers from the arginine treatments were slaughtered first, and the birds from the lysine treatments were slaughtered on the following day. Statistical Analyses Data in all experiments were subjected to a one-way analysis of variance using Minitab Data Analysis software. 4 Lysine and arginine requirements were estimated from weight gain, feed:gain, and breast meat weight using a single slope broken-line regression procedure (Robbins et al., 1979) and SAS software. 5 RESULTS Experiment 1 (0 to 2 wk) There were significant (P < 0.01) effects of dietary arginine and lysine levels on weight gain, breast muscle weight, and feed efficiency (Table 3). Feed intake was not

5 LYSINE AND ARGININE REQUIREMENTS 603 TABLE 4. Response of 2- to 4-wk-old broilers to arginine and lysine (Experiment 2) Arginine Lysine Weight Breast Feed Dietary Weight Breast Feed Dietary gain muscle intake Gain:feed lysine gain muscle intake Gain:feed arginine (%) (g) (g) (g) (g:g) (%) (g) (g) (g) (g:g) , , , , , , , , , , , , Pooled SEM Arginine NE 3 NE ND ± 0.01 Lysine 1.13 ± ± 0.06 ND NE requirement 2 requirement 2 1 Mean of four replicates of four chicks from 15 to 28 d; mean initial weight was 408 g per chick. 2 Requirement ± SE based on broken-line regression analysis. 3 Not estimated. Data did not conform to the regression model. 4 Not determined. different (P > 0.05) among arginine levels or among lysine levels. The arginine requirements for maximum weight gain, breast muscle weight, and feed efficiency were 1.24, 1.27, and 1.28% of the diet, respectively. The lysine requirements for maximum weight gain, maximum breast muscle weight, and maximum feed efficiency were 1.28, 1.32, and 1.21% lysine, respectively. Experiment 2 Average body weight gains, breast muscle weights, and feed intakes did not differ significantly (P > 0.05) among the dietary arginine levels (Table 4). Feed efficiency, however, was affected by dietary arginine (P < 0.01). According to the broken-line regression analysis, maximum feed efficiency occurred at 1.05% dietary arginine. Data for weight gain and breast muscle weight were not appropriate for the regression analysis because no plateaus in response were observed. There were no significant effects (P > 0.05) of lysine on weight gain, feed consumption, or feed:gain (Table 4). Only breast muscle weights were affected (P < 0.01) by increasing lysine levels. The lysine requirements for maximum weight gain and breast muscle weight were 1.13 and 1.21%, respectively. Feed efficiency responses were not appropriate for regression analysis. Experiment 3 Weight gain, breast muscle weight, feed intake, and feed efficiency (Table 5) were significantly affected by dietary arginine (P < 0.01). The arginine requirements for weight gain, breast muscle weight, and feed efficiency determined by broken-line regression were 0.92, 0.97, and 0.95% of the diet, respectively. The lysine requirements for maximum weight gain, breast muscle weight, and feed efficiency were 0.99, 0.99, and 1.00% of the diet, respectively. Experiment 4 In 5- to 8-wk-old broilers, body weight gain, feed efficiency, and feed consumption did not differ (P > 0.05) among the arginine levels (Table 6). The arginine requirement for maximum breast muscle weight was 0.83% of the diet. Requirements were not estimated for weight gain TABLE 5. Response of 3- to 6-wk-old broilers to arginine and lysine (Experiment 3) Arginine Lysine Weight Breast Feed Dietary Weight Breast Feed Dietary gain muscle intake Gain:feed lysine gain muscle intake Gain:feed arginine (%) (g) (g) (g) (g:g) (%) (g) (g) (g) (g:g) , , , , , , , , , , , , , , , , , , , , , , , Pooled SEM Arginine 0.92 ± ± 0.02 ND ± 0.03 Lysine 0.99 ± ± 0.02 ND 1.00 ± 0.02 requirement 2 requirement 2 1 Mean of four replicates of four chicks from 22 to 42 d; mean initial weight was 870 g per chick. 2 Requirement ± SE based on broken-line regression analysis. 3 Not determined.

6 604 LABADAN ET AL. TABLE 6. Response of 5- to 8-wk-old broilers to arginine and lysine (Experiment 4) Arginine Lysine Weight Breast Feed Dietary Weight Breast Feed Dietary gain muscle intake Gain:feed lysine gain muscle intake Gain:feed arginine (%) (g) (g) (g) (g:g) (%) (g) (g) (g) (g:g) , , , , , , , , , , , , , , , , , , , , , , , , Pooled SEM Arginine NE ± 0.02 ND 4 NE Lysine 0.81 ± ± 0.01 ND NE requirement 2 requirement 2 1 Mean of four replicates of four chicks from 36 to 56 d; mean initial weight was 1,675 g per chick. 2 Requirement ± SE based on broken-line regression. 3 Not estimated. Data did not conform to the regression model. 4 Not determined. and feed efficiency because the data did not conform to the regression model. The lysine requirements for maximum weight gain and breast muscle weight were 0.81% of the diet for both variables. Feed efficiency data were not appropriate for regression analysis. A summary of the estimated requirements for arginine and lysine are presented in Table 7. The regression equations for the one-slope regression analyses that generated the estimated requirements are presented in Table 8. Mortality Rate The average mortality rate for all the experiments was 2.7%. No effects of dietary lysine or arginine level were observed. DISCUSSION The estimated lysine requirements of 1.28, 1.32, and 1.21% for weight gain, breast muscle weight, and feed efficiency for broilers to 2 wk of age indicate that the lysine requirement is higher than 1.10% as suggested by the NRC (1994). These results are similar to those of others for total TABLE 7. Summary of lysine and arginine requirements (based on total amino acids) 1 Requirement (% of diet) Age Amino acid Weight gain Breast muscle Feed:gain 0 2 wk Arginine 1.24 ± ± ± 0.04 Lysine 1.28 ± ± ± wk Arginine * * 1.05 ± 0.01 Lysine 1.13 ± ± 0.06 * 3 6 wk Arginine 0.92 ± ± ± 0.03 Lysine 0.99 ± ± ± wk Arginine * 0.83 ± 0.02 * Lysine 0.81 ± ± 0.01 * 1 Requirement ± SE based on broken-line regression method of Robbins et al. (1979). *Data were not appropriate for regression analysis. dietary lysine (Morris et al., 1987; Morris and Abebe, 1990; Han and Baker, 1991; Surisdiarto and Farrell, 1991; Holsheimer and Ruesink, 1993). The lysine requirements for broilers at 2 to 4 wk of age were also slightly above the NRC (1994) recommendation of 1.10% for 0- to 3-wk-old broilers. The lysine requirements of 3- to 6-wk-old broilers, however, were similar to the NRC (1994) estimate of 1.00% for 3 to 6 wk, and the requirements that were determined by Han and Baker, All the variables used to predict the lysine requirement of 5- to 8-wk-old broilers resulted in estimates of the requirement that are slightly lower than the NRC (1994) requirement of 0.85% for 6- to 8-wk-old broilers. Increasing dietary lysine levels above 0.81% produced no response in body weight, breast muscle weight, or feed efficiency. Bilgili et al. (1992), Renden et al. (1994), and Hickling et al. (1990), however, observed responses in breast muscle yield at dietary lysine levels higher than 0.82%. The arginine requirements for body weight gain and breast muscle growth of 1.24 and 1.27% closely resemble the NRC (1994) requirement of 1.25% for 0 to 3 wk of age and are consistent with the results of Cuca and Jensen (1990) based on body weights and feed conversion. The arginine requirements for maximum weight gain, breast muscle growth, and feed efficiency of 3- to 6-wk-old broilers were lower than the value (1.10%) estimated by the NRC (1994). The arginine requirement of 5- to 8-wk-old broilers was markedly lower than the NRC (1994) estimate of 1.00%. Chickens fed practical diets based on corn and soybean meal and containing the crude protein levels indicated by the NRC (1994) would not be expected to be arginine deficient unless the dietary lysine level is greatly in excess of the requirement. Methionine is first-limiting, and lysine and arginine may be co-second limiting amino acids (Edmonds et al., 1985); thus, methionine is usually added, and lysine is frequently added, to practical diets in synthetic form. The data suggest that in a typical corn-soybeanbased diet, the diet could be formulated (with methionine and lysine supplements) to protein levels as low as 21.5,

7 LYSINE AND ARGININE REQUIREMENTS 605 TABLE 8. Regression equations 1 predicting the arginine and lysine requirements in Tables 3 through 6 Weight gain Breast muscle weight Feed efficiency Age Amino acid Regression 2 Regression 2 Regression wk Arginine y = (1.24 x) y = (1.27 x) y = (1.28 x) Lysine y = (1.28 x) y = (1.32 x) y = (1.21 x) 2 4 wk Arginine NE NE y = (1.05 x) Lysine y = (1.13 x) y = (1.21 x) NE 3 6 wk Arginine y = 1, ,928.1(0.92 x) y = (0.97 x) y = (0.95 x) Lysine y = 1, (0.99 x) y = (0.99 x) y = (0.99 x) 5 8 wk Arginine NE y = (0.83 x) NE Lysine y = 1, ,847.2(0.81 x) y = (0.81 x) NE 1 From one-slope broken-line regression analyses. 2 x = dietary arginine or lysine concentration (% of diet). y = weight gain (grams), breast muscle weight (grams) or feed efficiency (g gain/g feed consumed). 3 NE = Not estimated because data did not conform to the regression model. 19, 16, and 14% CP for 0 to 2-, 2 to 4-, 3 to 6-, and 5- to 8- wk-old broilers before arginine would become limiting in these diets. The lysine and arginine requirements as a percentage of CP content decreased as the age of broilers increased. Expressed as a percentage of CP, lysine and arginine requirements for all three variables were 6.0% (lysine) and 5.8% (arginine) in the 22% CP diet, 5.8% (lysine) in the 21% CP diet, 5.0% (lysine) and 4.8% (arginine) in the 20% CP diet, and 4.4% (lysine) and 4.3% (arginine) in the 18% CP diet. The requirements were slightly different from those of the NRC (1994) that estimated similar requirements for arginine and lysine based on a percentage of dietary CP for the entire growth period (5.5% arginine and 4.8% lysine). Excessive dietary lysine increases the requirement of chicks for arginine (Jones, 1964; D Mello and Lewis, 1970; Allen et al., 1972). Therefore, the surfeit of lysine content of the experimental diets might have resulted in overestimates of the arginine requirement. The ratio of lysine concentration in the diet to the estimated arginine requirement for maximum breast muscle yield is shown in Table 9. The ratio ranged from 1.13 to 1.26 for the ages for which the arginine requirement could be determined. There was little excess of lysine for 0 to 2 wk of age because the ratio was only 1.13, and the ratio of requirements of lysine to arginine was The lysine excess was higher at later ages. TABLE 9. Lysine:arginine ratios based on total arginine requirements 1 Dietary Dietary lysine Arginine Lysine:arginine Interval CP (%) level 2 (%) requirement (%) ratio wk wk wk wk Arginine requirements based on breast muscle growth; arginine requirement for breast muscle growth was not estimated for 2 to 4 wk. 2 Dietary lysine level in the diets used for investigation of the arginine requirement. 3 Dietary lysine level/arginine requirement. Published data (D Mello and Lewis, 1970) on the lysinearginine antagonism in broilers suggests that the arginine requirement may increase 0.1% of the diet for each 0.25% of dietary lysine in excess of the lysine requirement. This finding could mean that the arginine requirements for 0 to 2-, 3 to 6-, and 5- to 8-wk-old broilers are overestimated; the actual arginine requirements may be 0.04, 0.06, and 0.09%, respectively, lower than determined by regression analysis in these experiments. However, the lower estimates would be applicable only to diets with an ideal balance of lysine and arginine. Breast muscle growth has become a variable of interest in recent years because of the high economic value of this portion of the poultry carcass (Sibbald and Wolynetz, 1986; Hickling et al., 1990; Moran and Bilgili, 1990; Acar et al., 1991; Bilgili et al., 1992; Holsheimer and Ruesink, 1993; Renden et al., 1994). Breast muscle is 30% of the total edible meat and 60% of edible protein in the carcass (Summers and Leeson, 1985). The data from these experiments indicate that increasing dietary lysine and arginine supplementation increased breast muscle growth, but the levels required to maximize breast muscle weight during the first 2-wk overlap in their 95% confidence intervals with the requirements for maximum growth rate. It is interesting, however, that the lysine requirement for maximum breast muscle weight at 0 to 2 wk and 2 to 4 wk tended to be higher than the lysine requirement for maximum weight gain or feed efficiency. There was no evidence, for lysine or arginine, of a difference between the requirements for growth and those for breast muscle weight of 3 to 6- or 5- to 8-wk-old broilers. The estimated lysine requirement for breast muscle growth of the 0- to 2-wk-old broiler (1.32 ± 0.01%) based on breast muscle growth is substantially higher than the NRC (1984) or NRC (1994) estimates. The digestibility of ingredients was not determined in these experiments. However, digestible lysine and arginine requirements have been calculated from tables of feedstuff composition and amino acid digestibility in the NRC (1994) publication. The calculated digestible lysine and arginine requirements, based on breast muscle growth were 1.24 and 1.19% to 2 wk of age, 1.11% and ND for 2 to 4 wk of age, 0.92 and 0.92% for 3 to 6 wk of age, and 0.75 and

8 606 LABADAN ET AL. 0.78% for 5 to 8 wk of age, respectively. The digestible lysine requirements for 2 to 4- and 3- to 6-wk-old broilers, respectively, was close to the values of 1.12 and 0.87% reported by Han and Baker (1993, 1994) for 1 to 3- and 3- to 6-wk-old broilers. The regression analysis used in these experiments predicted the lysine and arginine requirements using brokenline regression that generally underestimates the actual requirements (Robbins et al., 1979). Thus, a margin of safety above the estimated requirements should be considered if the present data are used as a basis for formulation of broiler diets. ACKNOWLEDGMENTS The authors thank Archer Daniels Midland Company for funding in support of this project and ConAgra, Inc. for donating the chicks used in these experiments. The authors also acknowledge the assistance of Barbara Smagner in the preparation of the manuscript for publication. REFERENCES Acar, N., E. T. Moran, Jr., and S. F. Bilgili, Live performance and carcass yield of male broilers from two commercial strain crosses receiving rations containing lysine below and above the established requirement between six and eight weeks of age. Poultry Sci. 70: Allen, N. K., D. H. Baker, H. M. Scott, and H. W. Norton, Quantitative effect of excess lysine on the ability of arginine to promote chick weight gain. J. Nutr. 102: Bilgili, S. F., E. T. Moran, Jr., and N. Acar, Strain cross response of heavy male broilers to dietary lysine in the finisher feed: Live performance and further-processing yields. Poultry Sci. 71: Burton, E. M., and P. W. Waldroup, Arginine and lysine needs of young broiler chicks. Nutr. Rep. Int. 19: Cuca, M., and L. S. Jensen, Arginine requirement of starting broiler chicks. Poultry Sci. 69: D Mello, J.P.F., and D. Lewis, Amino acid interactions in chick nutrition. 3. Interdependence in amino acid requirements. Br. Poult. Sci. 11: Edmonds, M. S., C. M. Parsons, and D. H. Baker, Limiting amino acids in low-protein corn-soybean meal diets fed to growing chicks. Poultry Sci. 64: Grau, C. R., and M. Kamei, Amino acid imbalance and the growth requirements for lysine and methionine. J. Nutr. 41: Han, Y., and D. H. Baker, Lysine requirement of fast and slow growing broiler chicks. Poultry Sci. 70: Han, Y., and D. H. Baker, Effects of sex, heat stress, body weight and genetic strain on the dietary lysine requirement of broiler chicks. Poultry Sci. 72: Han, Y., and D. H. Baker, Digestible lysine requirement of male and female broiler chicks during the period three to six weeks posthatching. Poultry Sci. 73: Hickling, D., W. Guenter, and M. E. Jackson, The effects of dietary methionine and lysine on broiler chicken performance and breast meat yield. Can. J. Anim. Sci. 70: Holsheimer, J. P., and E. W. Ruesink, Effect on performance, carcass composition, yield, and financial return of dietary energy and lysine levels in starter and finisher diets fed to broilers. Poultry Sci. 72: Jones, J. D., Lysine-arginine antagonism in the chick. J. Nutr. 84: Kessler, J. W., and O. P. Thomas, The arginine requirement of the 4 7 week old broiler. Poultry Sci. 55: Moran, E. T., Jr., and S. F. Bilgili, Processing losses, carcass quality, and meat yields of broiler chickens receiving diets marginally deficient to adequate in lysine prior to marketing. Poultry Sci. 69: Morris, T. R., and S. Abebe, Effects of arginine and protein on chick s responses to dietary lysine. Br. Poult. Sci. 31: Morris, T. R., K. Al-Azzawi, R. M. Gous, and G. L. Simpson, Effects of protein concentration on responses to dietary lysine by chicks. Br. Poult. Sci. 28: National Research Council, Nutrient Requirements of Poultry. 8th rev. ed. National Academy of Sciences, Washington, DC. National Research Council, Nutrient Requirements of Poultry. 9th rev. ed. National Academy of Sciences, Washington, DC. Renden, J. A., E. T. Moran, Jr., and S. A. Kincaid, Lack of interactions between dietary lysine or strain cross and photoschedule for male broiler performance and carcass yield. Poultry Sci. 73: Robbins, K. R., H. W. Horton, and D. H. Baker, Estimation of nutrient requirements from growth data. J. Nutr. 109: Sibbald, I. R., and M. S. Wolynetz, Effects of dietary lysine and feed intake on energy utilization and tissue synthesis by broiler chicks. Poultry Sci. 65: Summers, J. D., and S. Leeson, Broiler carcass composition as affected by amino acid supplementation. Can. J. Anim. Sci. 65: Summers, J. D., S. Leeson, and D. Spratt, Yield and composition of edible meat from male broilers as influenced by dietary protein level and amino acid supplementation. Can. J. Anim. Sci. 68: Surisdiarto, and D. J. Farrell, The relationship between dietary crude protein and dietary lysine requirement by broiler chicks on diets with and without the ideal amino acid balance. Poultry Sci. 70: