The activity of and requirements for selected amino acids in growing female swine. 2. Methionine and cystine

The methionine/cystine efficiency of ten protein sources including that of different charges of the same protein source was ascertained in N balance experiments with a total of 60 female pigs in the live weight range of 35-50 kg. The variability of the derived sulfur amino acids (SAS) efficiency coefficient (Csas) ranged between 0.64... 0.91 based on the SAS efficiency of casein as a standard. There was an analogous differentiation for the derived requirement values on the basis of the analysed methionine/cystine values of the proteins. For a protein retention of 100 g/day and a live weight of 40 kg, 6.2g methionine/cystine was ascertained based on the highest SAS efficiency (Csas = 1) as yet.     

The efficiency of and requirements for selected amino acids in growing female pigs. 3. Threonine

With the help of an N utilization model by Gebhardt (1963) and its further development the threonine efficiency coefficients (kThr) of wheat, barley, maize, rye and peanut oil meal of different charges with a supply of L-lysine monohydrochloride, DL-methionine and DL-tryptophan was ascertained with a total of 59 female pigs of the local breed (35-45 kg live weight) by means of an N balance method. The variation range of kThr was between 0.61 and 0.87 based on a threonine effectivity of wheat gluten with lysine as standard. The derived threonine requirement for 100 g daily protein retention with a live weight of 40 kg was ascertained as 6.9 g (kThr = 1) and 9.6 kg (kThr = 0.71 as mean values of the protein sources studied). The proof of threonine limitation in the protein sources was provided by the supplementation of DL threonine.     

Results of the effectiveness and requirements of selected amino acids on growing female swine. 5. Combinations of protein sources for the derivation of lysine effectiveness using the difference method

On the basis of 87 N balance trials with growing female pigs the possibility of deriving lysine effectivity coefficients according to the difference method for proteins rich in lysine, based on proven additive relations for amino acid effectivity coefficients (Liebert et al., 1987b). The results from 9 proteins of various charges show that nutrition-physiologically relevant conclusions for lysine effectivity could be drawn under the conditions chosen. Thus the range of application of the chosen method of the registration of the effective amino acid quota in feed proteins could be significantly extended.     

Effect of nonessential amino acids on nitrogen retention in growing pigs fed on a protein-free diet supplemented with sulphur amino acids, threonine and tryptophan

Two N balance experiments were conducted on growing pigs to study the effect of essential and nonessential amino acids added to a protein-free diet on N retention. In Expt. 1, the addition of sulphur amino acids, threonine and tryptophan to a protein-free diet at levels two times the maintenance requirements reduced (p > 0.1) daily N loss from –131 to –108 mg/kg^0.75. A further addition of nonessential amino acids equivalent to 250 mg N/kg^0.75/d resulted in a marked increase (p < 0.01) in daily N retention to 28 mg/kg^0.75. In Expt. 2, nonessential amino acids were added to a protein-free diet supplemented with sulphur amino acids, threonine and tryptophan at levels corresponding to 100, 200 and 300 mg N/kg^0.75/d. N retention increased linearly as dietary nonessential N increased. The slope of the best-fit regression line indicated that the marginal efficiency of nonessential N utilization for protein accretion was 0.26. The results suggest that nonessential amino acids may be a limiting factor for the re-utilization of amino acids released by body protein breakdown or that they may serve as precursors for de novo synthesis of amino acids by gut microorganisms, thus contributing to the amino acid requirements of the pig.     

Efficiency of amino acid utilization in the growing pig at suboptimal levels of intake: lysine, threonine, sulphur amino acids and tryptophan

A series of N balance experiments using growing pigs was conducted to study the efficiency of utilization of lysine, threonine, sulphur amino acids and tryptophan and to estimate their maintenance requirements. Purified diets based on casein and crystalline amino acids as the sole source of N contained graded levels of each amino acid, corresponding to expected protein accretion rate of 0, 33, 66, 99 and 132 g/day, respectively. N retention increased linearly (p < 0.01) as the dietary concentration of the limiting amino acid increased. Based on linear regression equations relating amino acid deposition in body protein to amino acid intake, marginal efficiencies of ileal digestible amino acid utilization were calculated to be lysine 0.91, threonine 0.83, sulphur amino acids 0.85 and tryptophan 0.66. Extrapolating the regression equations to zero N retention, the daily requirements of amino acids for N equilibrium were estimated to be (mg/kg(0.75)) lysine 39, threonine 49, sulphur amino acids 46 and tryptophan 16.     

Effects of dietary methionine and lysine sources on nutrient digestion, nitrogen utilization, and duodenal amino acid flow in growing goats

This study investigated the effects of supplementation of various sources of Met and Lys on nutrient digestion, N utilization, and duodenal AA flows in growing goats. Four 4-mo-old Liuyang Black wether goats were used in a 4 x 4 Latin square experiment and were assigned to 4 dietary treatments: (1) control, (2) control + lipid-coated Met-Zn chelate and Lys-Mn chelate (PML), (3) control + Met-Zn chelate and Lys-Mn chelate (CML), and (4) control + dl-Met, l-Lys-HCl, ZnSO(4).7H(2)O, and MnSO(4).H(2)O (FML). Compared with control, PML reduced (P < 0.05) ruminal NH(3) concentration, urinary N excretion, and plasma urea N concentration and increased (P < 0.05) the activity of ruminal endo-1,4-beta-d-glucanase and beta-glucosidase, the duodenal flow of N, N retention (g/d as well as % of absorbed N), the duodenal flows of Met, Lys, His, Val, and total essential AA, and plasma concentrations of Lys, Val, Phe, and total essential AA. Supplementing Zn-Met and Mn-Lys chelates had similar (P > 0.05) but lesser effects on these measures compared with PML, and the effects on most of the measures were not statistically significant (P > 0.05) when compared with control. Supplementing free-form Met and Lys had no effects compared with control (P > 0.05). The results indicate that lipid coating and chelating of AA provide a protection, and to a lesser extent by only chelating, of the AA from microbial degradation in the rumen and possibly has effects on rumen fermentation, which increases MP supply. This technology could improve productive performance and be of potential benefit to ruminant production if cost-effective products are developed.     

Apparent digestibility of nitrogen and amino acids in protein feedstuffs by growing pigs

Eight digestion trials were conducted with pigs fitted with ileal T-cannulas to determine the apparent digestibilities of N and amino acids in common protein feedstuffs. Trial-to-trial variation was minimal as determined by the variation in digestibilities for soybean meal, which was evaluated in each trial. Apparent digestibilities varied widely; ileal N digestibility ranged from 88 to 63%, and ileal lysine digestibility ranged from 93 to 40%. In general, ring-dried blood meal, corn gluten meal, Menhaden fish meal, poultry-by-product meal and extruded whole soybeans were the most digestible, followed by canola meal, sunflower meal, peanut meal and meat and bone meal. Cottonseed meal and feather meal were the least digestible. Mean values for each feedstuff agree well with published data. Variation in digestibilities among samples of the same feedstuff was greater for the meat and bone meals. Regression of ileal essential amino acid digestibilities on ileal and fecal N digestibility indicated that amino acid digestibilities can be predicted more precisely from ileal N digestibility than from fecal N digestibility. However, neither ileal nor fecal N digestibility could be used with a high degree of certainty to predict ileal amino acid digestibilities.     

Performance dependent lysine requirement of fattening pigs. 3. Effect of amino acid and energy intake on fat, protein and lysine deposition of swine

The gain in structural matter had a linear course with a corresponding feeding intensity and depending on the period of fattening. However, the animals given high-energy diets deposited 130 g protein per day during the first fattening period, this deposition being compensated in the course of further growth by a considerably lower deposition in the sense of aequifinality. Up to a live weight of 70 kg, animals subjected first to restricted feeding and then to fully balanced feeding revealed the highest protein deposition during the last period of fattening, this fact emphasizing the leanmeat character of the animal material used. The daily fat deposition was found clearly determined by energy intake and independent of amino acid supply. Lysine conversion was influenced by the intake of lysine and energy. Under feeding to norm it reached some 40 and 30% during the first and second periods of fattening, respectively.     

An estimate of the methionine requirement and its variability in growing pigs using the indicator amino acid oxidation technique

Although AA requirements for the mean of a population of growing pigs have been established using traditional methods, there are no estimates of the variability within the population and whether this variation differs among AA. With the increased use of supplemental Lys in pig diets, there will be an increased need to supplement Met, commonly the second or third limiting AA in corn-soybean diets. The indicator AA oxidation method allows repeated measurements in a short period of time so that the AA requirement can be determined for individual pigs at a similar physiological stage. The objective of this study was to determine the mean Met requirement in individual gilts and to estimate the related variability. Six individually housed female pigs (initial BW = 8.8 kg, SD 1.5) each received diets providing 6 levels of dl-Met. The isonitrogenous and isoenergetic diets contained 0.187, 0.250, 0.290, 0.320, 0.350, and 0.377% Met (analyzed, as-fed basis). Cysteine (0.48%) and Lys (1.44%) concentrations were similar for all diets. Pigs were adapted for 6 d to the basal corn-soybean meal diet (0.187% Met), which was offered at 95 g/kg(0.75) of BW to ensure complete consumption of the test diets. During 4-h oxidation studies, 313.4 kBq, (SD 35.6) of L-[1-(14)C]Phe was mixed with each of 8 half-hourly meals, and expired CO(2) was collected. The breakpoint in Phe oxidation, representing the Met requirement, and its variability, was determined using 2-phase linear regression. Phenylalanine oxidation decreased as the Met content increased from 0.187 to 0.29%. Phenylalanine oxidation was not different (P > 0.2) for diets ranging from 0.320 to 0.377% Met. The dietary Met requirement varied from 0.320 to 0.373% for individual pigs. The mean Met requirement for individual pigs was determined to be 0.340% of diet (SD = 0.024%, CV= 7.1%), with 0.340, 0.364, and 0.388% covering the requirement of 50, 66, and 95% of the population, respectively. The present mean population estimate was similar to the recommended dietary Met concentration of 0.325% for pigs of this BW and feed intake. To maximize profitability, Met levels in starter pig diets should be determined, depending on the cost of crystalline Met and the fraction of the population whose requirement is to be met.     

氨基酸蛋白粉替代鱼粉对生长畜肥猪的影响

选用45日龄、体质量相近、健康的杜×长×大三元杂交猪125头,研究氨基酸蛋白粉替代鱼粉对生长育肥猪生长性能及饲养成本的影响.研究结果表明,氨基酸蛋白粉与鱼粉在设定的范围内(3%)对生长育肥猪生长性能的影响差异不显著,即添加一定比例的氨基酸蛋白粉或鱼粉(1%～3%)均可显著提高生长育肥猪的生长性能,添加氨基酸蛋白粉和鱼粉均可显著降低饲养成本(P＜0.05);在第二阶段添加3%的氨基酸蛋白粉替代鱼粉可以降低饲养成本.     

Ileal digestibility of protein and amino acids from canola meal in weaned piglets and growing pigs

Two experiments were conducted to measure the apparent ileal digestibility coefficients (AID) of protein and amino acids from canola meal (CM) and a pelleted canola meal (PCM) and their effect on specific activity (SA) of pancreatic proteases in weaned piglets and growing pigs. In experiment one, 24 piglets weaned at 17 days and weighing 5.5 kg were used. Treatments were a reference diet with 200 g of crude protein (CP) kg^− 1 elaborated with casein (C) as the sole protein source, a diet containing C–CM and a diet containing C–PCM. These diets were obtained using the reference diet plus 100 g kg^− 1 of CM or PCM that substituted an isoproteic mixture of casein and maize starch from reference diet, so that the AID coefficients for their protein and amino acids could be calculated by difference. In experiment two, nine castrated pigs weighing 39.5 kg were used. Treatments were a reference diet with 160 g of CP kg^− 1 elaborated with casein (C) as the sole protein source, diet C–CM and diet C–PCM. These diets were obtained using the reference diet plus 300 g kg^− 1 of CM or PCM that substituted an isoproteic mixture of casein and maize starch from reference diet. In piglets, the AID coefficients for casein were highest (P < 0.05), those of PCM were intermediate, and those of CM were the lowest. In older pigs, the AID coefficients for casein were highest, and those of CM and PCM were similar (P > 0.05). The SAs of chymotrypsin, trypsin and carboxypeptidases A and B were lower in piglets than in heavier pigs. Moreover, the SAs of trypsin, chymotrypsin, and carboxypeptidase B were lower (P > 0.05) in animals fed casein. The results showed in piglets that whereas CM was less digestible, pelleted canola meal improved protein and amino acid ileal digestibility, resulting in similar AID coefficients to those of growing pigs.     

精油对生长猪蛋白质和氨基酸等回肠末端表观消化率的影响

试验旨在通过采用T型瘘管法,研究精油对生长猪蛋白质和氨基酸等回肠末端表观消化率的影响。试验选用6头(杜×长×大)去势公猪([28.6±1.3)kg],采用3×3双拉丁方试验设计,分别饲喂正对照日粮:玉米-豆粕型基础日粮+抗生素;负对照日粮:无抗基础日粮;精油组日粮:负对照+0.01%精油。每个试验期为7 d,前5 d为适应期,后2 d为食糜收集期。结果表明,在日粮中添加精油可提高(P<0.05)蛋白质、能量、精氨酸、赖氨酸、亮氨酸、色氨酸、蛋氨酸、丙氨酸、总必需氨基酸、总氨基酸的回肠末端表观消化率,并有提高干物质、苏氨酸、天冬氨酸、丝氨酸和酪氨酸表观消化率的趋势(P<0.10)。在日粮中添加0.01%的精油可提高生长猪蛋白质、能量、总必需氨基酸和总氨基酸的回肠末端表观消化率,并有提高干物质表观消化率的趋势。     

Effects of porcine somatotropin administration on the responses to dietary lysine and a near-ideal blend of amino acids for growing pigs

Two experiments were conducted to assess the effects of porcine ST (pST) on the responses to a near-ideal blend of AA for pigs from 22 to 60 kg BW. Eighty Hampshire × Yorkshire gilts (40 gilts/experiment) were individually penned and assigned to a 4 × 2 factorial arrangement of treatments, consisting of 4 diets with and without pST injection. A fortified corn-soybean meal basal diet was formulated to contain 1.50% total Lys and Thr, Met, and Trp were added to obtain a near-ideal blend of these AA relative to Lys. In 3 additional diets, Lys was reduced to 1.25%, 1.00%, or 0.75% by diluting the basal diet with cornstarch, cellulose, and sand, such that the diets also contained the same ratios of AA. Pigs that received pST were administered a daily intramuscular injection of 2 mg of pST. Data from the 2 experiments were pooled. Administration of pST increased ADG (P < 0.01), G:F (P < 0.01), and LM area (P < 0.01), and decreased ADFI (P < 0.03), last rib backfat (P < 0.01), and 10th rib backfat (P < 0.01). Also, estimated carcass muscle and calculated lean gain increased (P < 0.01) in pST-treated pigs. Administration of pST also increased (P < 0.01) the percentage, total gain and accretion rate of water, protein, and ash in the carcass, and decreased (P < 0.01) the percentage, total gain, and accretion rate of carcass fat. Growth rate, G:F, and carcass traits improved (P < 0.01), percentage of carcass proteinand water increased (P < 0.01), and carcass fat percentage decreased (P < 0.01) with increasing dietary Lys. The percentage, total gain, and accretion rate of carcass protein increased to a greater extent in pST-treated pigs than in untreated pigs, resulting in a pST × Lys interaction (P < 0.05). The results indicated that pST improves performance, leanness, and protein accretion in pigs from 22 to 60 kg BW, and that these responses to dietary Lys and a near-ideal blend of AA is greater in growing pigs treated with pST than untreated pigs.     

Digestibility of amino acids in corn, corn coproducts, and bakery meal fed to growing pigs

The objectives of this experiment were to determine the apparent ileal digestibility and the standardized ileal digestibility (SID) of CP and AA in bakery meal, corn gluten meal, corn gluten feed, corn germ meal, and hominy feed and to compare these values with the apparent ileal digestibility and SID of CP and AA in corn and distillers dried grains with solubles (DDGS). Eight growing barrows (initial BW: 82.5 ± 5.5 kg) were randomly allotted to an 8 × 8 Latin square design with 8 diets and 8 periods. Diets contained corn, DDGS, bakery meal, corn gluten meal, corn gluten feed, corn germ meal, or hominy feed as the sole source of protein and AA. An N-free diet was used to measure basal endogenous losses of AA and protein. Pigs were fed experimental diets for eight 7-d periods, with ileal digesta being collected on d 6 and 7 of each period. Results indicated that the SID of Lys in corn gluten meal (78.7%) was greater (P < 0.01) than in DDGS, bakery meal, corn germ meal, and hominy feed (46.0, 48.4, 68.4, and 58.8%, respectively). The SID of all indispensable AA except Arg, Leu, and Met in bakery meal were not different from those in DDGS. The SID of Arg, His, Leu, and Met in corn gluten feed were less (P < 0.01) than in corn, but the SID of all other indispensable AA in corn gluten feed were not different from those in corn. However, for most indispensable AA, the SID in corn gluten feed was not different from the SID in DDGS. The SID of all indispensable AA in corn germ meal, except Arg, His, Leu, and Met, were not different from the SID in corn. Likewise, the SID of all indispensable AA in corn germ meal, except Arg and Leu, were not different from those in DDGS. The SID of Ile, Met, Phe, and Val in hominy feed were less (P < 0.01) than in corn, but the SID of the remaining indispensable AA in hominy feed were not different from the SID of indispensable AA in corn. All indispensable AA in hominy feed also had SID values that were not different from the SID values of AA in DDGS, except for Arg and Lys, which had greater (P < 0.01) SID than in DDGS. In conclusion, bakery meal had SID values of most AA that were less than in corn, but corn gluten meal had SID values for most AA that were greater than the SID of AA in corn, bakery meal, and corn coproducts.     

The effectiveness of and requirements for selected amino acids in growing female swine. 6. Summarizing discussion, evaluation and recommendations for use of the method presented

Physiologically based statements on the effectivity of lysine, methionine/cystine and threonine of protein sources as well as on the requirement of these amino acids depending on performance were derived on the basis of a total of 568 N balance measurings at growing female fattening pigs in the live weight range between 30 and 50 kg (Liebert, 1986) with the application of the N utilization model by Gebhardt (1963) as well as of particular further developments by the linking of N utilization and the utilization of the respective limiting amino acid. By means of combining protein sources with known amino acid effectivity, the additivity principle for content values of effective amino acid in the feed protein (c.k) suggested as criteria was verified. On the whole, it could thus be proved that the suggested method can decisively contribute to the elaboration of a closed system of quality assessment and requirement assessment depending on performance as well as of supply covering requirements of growing pigs. The advantages in particular over the 'slope ratio' method are emphasized.     

Influence of dietary protein level and the amino acids methionine and lysine on leather properties of blue fox (Alopex lagopus) pelts.

The influence of dietary protein, methionine, and lysine on leather quality in blue fox pelts was studied. The pelt material originated from animals in two consecutive feeding trials (Exp. 1 and Exp. 2) with three protein levels: conventional, slightly lowered, and very low. The two lowest protein diets were fed as such or as supplemented with methionine or with lysine (lysine only in Exp. 2). The following physical leather properties were measured: breaking load (BRL), tensile strength (TEN), relative elongation at break (PEB), straining of skins at pelting, and shrinkage at dressing. A decline in the dietary protein content reduced BRL and, hence, leather firmness, and increased straining and the corresponding shrinking in Exp. 1. The supplemented methionine tended to improve leather strength and elasticity by increasing TEN and PEB in Exp. 1, whereas lysine elicited no response. Methionine supplementation at the slightly lowered protein level increased BRL in both experiments by almost 10% as compared with the respective non-supplemented diet. We conclude that with high protein quality diets, a level of 200 g/kg DM (as digestible protein) appears to be adequate for producing pelts with firm, elastic leather, provided that an adequate amount of methionine is included in the diet.     

Influence of the dietary ratio between sulphur containing amino acids and lysine on performance of growing-finishing pigs fed diets with various lysine concentrations.

This study was conducted to determine the optimal ratio between sulphur containing amino acids and lysine in diets for growing-finishing pigs. Therefore, a total of five trials was carried out in which growing-finishing pigs (live weight range between 53 and 105 kg) were fed diets with various concentrations of lysine (0.62, 0.70 and 0.78%) and various ratios between sulphur containing amino acids to lysine. The diets contained 12.9 MJ ME per kg and 13.5% CP; the ratio between sulphur containing amino acids to lysine was adjusted by individual supplementation of the diets with DL-methionine. Increasing dietary levels of lysine from 0.62 to 0.78% continuously increased daily body weight gains and improved feed conversion efficiency as well as carcass characteristics. There was no significant interaction between the dietary lysine supply and the ratio between sulphur containing amino acids to lysine on animal performance parameters. This means that the effect of the ratio of sulphur containing amino acids to lysine was similar for various dietary lysine concentrations. The optimum ratio between sulphur containing amino acids to lysine according to quadratic regression analysis was 0.60, for both, growth and feed conversion. Reducing the ratio between sulphur containing amino acids to lysine from 0.59 to 0.53 and 0.47 reduced body weight by 3 and 12%, resp., and elevated the feed conversion ratio by 2 and 12%, resp. An increase of the ratio between sulphur containing amino acids to lysine from 0.59 to 0.65 failed to increase the animal performance. In contrast to animal performance parameters, optimum carcass characteristics (eye muscle area, fat area above eye muscle, meat-fat ratio and lean percentage) were achieved already at a ratio of sulphur containing amino acids to lysine of 0.53.     

Involvement of food intake in the decreased energy retention associated with single deficiencies of lysine and sulphur-containing amino acids in growing chicks.

1. Growth and energy utilisation were determined in growing chicks fed ad libitum on diets deficient either in lysine (5.95 g/kg) or in sulphur-containing amino acids (SAA, 3.5 g/kg). Food intake, body weight gain, energy retained as protein and as fat, and total energy retention were significantly (P less than 0.05) reduced by single deficiencies of either lysine or SAA. 2. Another two experiments were conducted to determine if the decreased total energy retentions in chicks fed on diets deficient in lysine (experiment 3) or SAA (experiment 4) were associated with reduced food intake, by using tube-feeding to control the amount and pattern of food consumption. Chicks fed on diets deficient in lysine or SAA retained less energy as protein and more energy as fat than the control chicks. Neither total energy retention nor heat increment was affected by these deficiencies. Total energy retention was proportional to metabolisable energy (ME) intake alone. 3. It is concluded that the decreased total energy retentions caused by single deficiencies of lysine and SAA were associated with decreased food intake.     

Muscle growth and plasma concentrations of amino acids, insulin-like growth factor-I, and insulin in growing pigs fed reduced-protein diets

Twenty barrows were used to determine if partial replacement of protein-bound AA with crystalline AA (CAA) reduces AA use for muscle tissue and whole-body growth. Barrows (44.2 +/- 1.3 kg of BW) were assigned to 4 diets in a randomized complete block design. Diets consisted of 16.1% CP with no CAA, and 12.8, 10.1, and 7.8% CP containing CAA. As the CP concentration decreased, CAA were gradually increased to meet requirements on a true ileal digestibility basis. Barrows were weighed on d 0 and 13. Blood samples were collected before the morning feeding on d 0, 6, and 12 (prefeeding), and 2 h after the morning feeding on d 13 (postfeeding). Pigs were euthanized on d 13, and liver and right LM were removed and weighed. The reduction in the dietary CP concentration linearly decreased (P < 0.01) ADG, G:F, LM weight, and the CP content of LM. Reducing the CP concentration decreased pre- and postfeeding plasma concentrations of IGF-I (linear, P < 0.01) and insulin (linear, P < 0.10). The reduction in the dietary CP concentration increased prefeeding plasma concentrations of Ala, Gln, Gly, and total AA but decreased Arg, Asn, His, Ile, Phe, Trp, and Tyr (linear, P < 0.05). Plasma concentration of total indispensable AA decreased initially and increased thereafter as the dietary CP concentration decreased from 16.1 to 7.8% (quadratic, P < 0.01). The reduction in the dietary CP concentration increased postfeeding plasma concentrations of Ala, Lys, Met (linear, P < 0.01), and Gly (linear, P = 0.073) and decreased Asn, Ser, Tyr, Arg, His, and Leu (linear, P < 0.05). Plasma concentrations of Ile, Phe, Thr, Trp, and Val decreased initially and increased thereafter as the dietary CP concentration decreased from 16.1 to 7.8% (quadratic, P < 0.05). In muscle tissue, concentrations of free Ala, Asp, Glu, Gln, Gly, and Lys increased (linear, P < 0.05) as the dietary CP concentration decreased. Concentrations of free His, Ile, Phe, Thr, Trp, and Val in muscle tissue decreased initially and increased thereafter as the dietary CP concentration decreased from 16.1 to 7.8% (quadratic, P < 0.05). In summary, the reduction in the dietary protein-bound AA decreased whole-body and LM growth, altered the free AA pool profile in muscle tissue, and decreased plasma insulin and IGF-I. As the replacement of protein-bound AA with CAA increased, 1) free Ala and Gln in muscle tissue increased, indicating an increase of muscle tissue protein breakdown; and 2) utilization of indispensable AA in muscle tissue decreased.