Essential and Nonessential Amino Acid Composition of Pigs from Birth to 145 Kilograms of Body Weight, and Comparison to Other Studies 1,2

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1 Essential and Nonessential Amino Acid Composition of Pigs from Birth to 145 Kilograms of Body Weight, and Comparison to Other Studies 1,2 D. C. Mahan 3 and R. G. Shields, Jr. 4 Animal Sciences Department, The Ohio State University, and The Ohio Agricultural Research and Development Center, Columbus ABSTRACT: The amino acid composition of the body components (carcass, hair, whole blood, and a composite of the other body tissues) were determined from a total of 81 crossbred pigs at 10 weight intervals from birth to 145 kg body weight. Body component amino acid compositions (g/100 g protein) were multiplied by their respective protein contents, resulting in calculated whole-body amino acid compositions. From 8.5 to 145 kg body weight, the amino acid compositions were similar within each body component but differed between body components. There was a higher concentration of carcass lysine, arginine, and histidine ( P <.01) in the carcass, and isoleucine ( P <.12), threonine ( P <.15), and methionine ( P <.08) tended to be higher than in the composite of the other body tissue. Whole blood was, however, higher in leucine, valine, and lysine, and hair was higher in cystine than the carcass. The relative concentration of lysine in the whole body increased to about 37 kg body weight and reached a plateau, whereas the other essential amino acids increased to 8.5 kg and then reached a plateau. Tryptophan, however, decreased from birth to 8.5 kg and then remained at a similar concentration to 145 kg body weight. Whole-body amino acid composition of pigs in our study was generally similar to that noted in other scientific reports, but there was a wide variation in amino acid values between studies. Key Words: Amino Acids, Lysine, Growth, Development, Pigs 1998 American Society of Animal Science. All rights reserved. J. Anim. Sci : Introduction Munks et al. (1945) had suggested the idea of evaluating the amino acid requirements of laying hens based on their body tissue composition. Mitchell (1950) subsequently adopted this concept for all nonruminants but recommended that the dietary amino acid requirements be expressed as a ratio of each to one specific amino acid. Lysine has thus been used as the reference amino acid because its maintenance requirement is considered low (Baker, 1997). However, because of the unknown bioavailabilities of the essential amino acids of the different feedstuffs 1 Salaries and research support provided by state and federal funds appropriated to The Ohio Agric. Res. and Dev. Center, The Ohio State Univ., manuscript no Appreciation is expressed to R. Sabine, G. Smith, and D. Hickman for data and tissue collection, to Analytical Bio Chemistry Laboratories for the amino acid analyses, and to M. Milligan for typing the manuscript. 3 To whom correspondence should be addressed: Anim. Sci. Dept., The Ohio State Univ., 2027 Coffey Rd., Columbus. 4 Present address: Heinz Pet Products, Newport, KY. Received May 16, Accepted September 26, used in swine diet formulations, this concept was never widely applied by nutritionists until recently. In 1980, Cole suggested that the ratio of dietary amino acids relative to lysine be used to formulate swine diets and originated the term ideal protein. In 1981, the British Agriculture Research Council (ARC) adopted this concept in making dietary amino acid recommendations for swine. Because the ideal protein concept is largely based on the body s amino acid composition, several studies have evaluated the effect of sex, body weight, and genotype on whole-body amino acid composition of pigs. With increasing emphasis on reducing environmental N pollution, there is a need to provide combinations of dietary protein sources and synthetic amino acids that will minimize N content in the excrement. This along with the use of computer modeling and the trend toward phase feeding of pigs has brought about a resurrection of the initial concept proposed by Munks et al. (1945) and Mitchell (1950). Thus, we evaluated the relative amino acid composition of different body components of pigs at intervals from birth to 145 kg BW, calculated the whole-body amino acid content from these components, and then compared the results to other scientific studies. 513

2 514 Materials and Methods The total body tissue from 81 crossbred ([Hampshire Yorkshire] Duroc) pigs that had been used in a previous study were used to determine the amino acid composition at various stages of development (Shields et al., 1983). Nine pigs were killed at birth, and eight each at weaning (28 d), 20 kg BW, and at about 15-kg weight increments to a final weight of 145 kg. Gilts and barrows were represented equally within each weight group except for neonatal pigs. The selection of pigs, their management, and feeding regimen were previously reported (Shields et al., 1983). Slaughter techniques involved removal of the hair, blood, and digesta from the intestinal tract. This process was followed for all pigs between 8.5 to 145 kg BW, whereas neonatal pigs did not have their hair and blood removed when killed. The head, internal body organs, forelegs, and body trim ( HOLT) were combined and kept separate from the carcass, weighed, and frozen until later analyzed. The carcass and HOLT were ground and mixed separately and a homogenous sample was obtained, dried, defatted, and analyzed for amino acids. The equipment and procedures used for grinding the carcass and HOLT and the method of subsample collection were previously described (Shields et al., 1983). Blood was not collected at slaughter, but whole blood samples were obtained from the vena cava from a set of six fed pigs from the nine weight groups. These samples were pooled within group, frozen, and later analyzed for their protein and amino acid concentrations. Hair samples were obtained from three pigs of three weight groups (20, 80, and 140 kg BW) pooled within weight group, washed with alcohol and ether, dried, and analyzed for crude protein and amino acids. The whole blood, hair, carcass, and HOLT were analyzed for their amino acids by gas-liquid chromatography as outlined by Kaiser et al. (1974). In this procedure the use of ultrasonication under vacuum to remove dissolved air before acid hydrolysis (6 N HCl) has prevented the oxidation of the sulfur amino acids. Tryptophan was analyzed separately after hydrolysis in an alkaline medium. Protein content of the various body components was determined with the Kjeldahl procedure (AOAC, 1980). The protein content of the carcass and HOLT was previously reported (Shields et al., 1983) but is included herein for completeness. The content of each individual amino acid was subsequently calculated on a grams/100 grams of protein basis for each body component. The average amino acid composition of whole blood and hair was used to calculate whole-body amino acid composition from 8.5 to 145 kg BW. We assumed that hair represented.25% of total body weight and that total blood volume declined from 7 to 4% from 8 to 145 MAHAN AND SHIELDS kg BW based on the data of Kauffman et al. (1986). The quantity of body protein in each body component was multiplied by its relative amino acid compositions to calculate whole-body amino acid composition. The amino acid composition data from 8.5 to 145 kg BW were analyzed as a 2 9 factorial experiment in a split-plot design with pig weight as the main plot and body component as the subplot. The data were analyzed by the General Linear Models procedure of SAS (1985). The neonatal pigs were excluded from this analysis because their hair and blood had not been separated when the animals were killed. Amino acid composition of each component was evaluated by regression analysis over the nine weight groups. Because there was no major effect of pig weight on amino acid composition, the comparison of the four body components (carcass, HOLT, blood, and hair) were analyzed as a completely randomized design with the least squares analysis of variance procedure of SAS (1985). Treatment contrasts were analyzed by LSD only after a significant treatment response ( P <.05) occurred. The real mean and SE of each component are reported in tabular form. During the course of laboratory analyses, the sex identification was lost and could not be used in the statistical model. Our previous results, however, had demonstrated no difference in protein content between the sexes when carcasses were adjusted to a dried, fat-free basis. Siebrits et al. (1986) and Kyriazakis et al. (1993) also indicated no difference in the relative whole-body amino acid composition between the sexes. Results The essential and nonessential amino acid composition in the carcass and HOLT body components from 8.5 to 145 kg BW are presented in Tables 1 and 2, respectively. Individual essential and nonessential amino acid compositions within the carcass and HOLT, when expressed on a grams/100 grams of protein basis were similar within each body component between 8.5 and 145 kg BW (Table 1). There was, however, a difference in amino acid compositions between the two body components. The concentrations of arginine, histidine, and lysine were higher ( P <.01) in the carcass than in the HOLT body component, and isoleucine ( P <.12), methionine ( P <.08), and threonine ( P <.15) also tended to be higher (Table 1). The only nonessential amino acid that differed between these two body components was glutamic acid, which was higher ( P <.01) in the carcass (Table 2). When the amino acids (g/100 g protein) in the carcass and HOLT were summed, the carcass had an approximately 10% higher ( P <.01) total essential amino acid content (Table 1). Although the carcass contained bone and skeletal muscle, the latter tissue was considered to compromise the major portion of

3 PIG AMINO ACID COMPOSITION 515 Table 1. Essential amino acid composition of body components of pigs from 8 to 145 kg body weight (g/100 g protein) Amino acid and Live wt, kg: body component Empty body wt, kg: Avg SEM Arg Carcass HOLT a b His Carcass HOLT b Ile Carcass HOLT Leu Carcass HOLT Lys Carcass HOLT b Met Carcass HOLT Phe Carcass HOLT Thr Carcass HOLT Trp Carcass HOLT Val Carcass HOLT Total Carcass b HOLT a HOLT = head, internal organs, forelegs, and body trim. b Significant responses ( P <.01) between the carcass and HOLT. this component. These results therefore imply that 1) genotypes that develop more muscle have a higher dietary requirement for all essential amino acids and 2) there are specific essential amino acids necessary in higher quantities for muscle than for nonmuscular tissue development. Kyriazakis et al. (1993) also reported that the concentration of whole-body lysine and histidine increased during the period of rapid muscle development. Average essential and nonessential amino acid compositions of the carcass, HOLT, whole blood, and hair, when expressed on a grams/100 grams of protein basis, are presented in Table 3. Amino acid values for the carcass and HOLT components were derived from the weight groups between 8.5 and 145 kg BW (Tables 1 and 2, respectively). The water content of whole blood declined linearly ( P <.01) from 84.6 to 77.5% from 8.5 to 145 kg BW, similar to that of wholebody water (Shields et al., 1983). When the amino acid composition from whole blood was compared (g/ 100 g protein) at the various weights, the amino acid compositions were similar ( P >.15). There was no difference in the water content and amino acid composition of pig hair between the three weight groups ( P >.15), and the values were averaged. Although many of the blood amino acid compositions differed from the carcass and HOLT, whole blood leucine and valine concentrations were twofold higher ( P <.05) than those in the carcass or HOLT. Lysine and phenylalanine were higher ( P <.05) in whole blood than in the carcass and HOLT body components. Arginine, isoleucine, and methionine were lower ( P <.05), but hydroxyproline was markedly lower ( P <.05) in whole blood than in the carcass and HOLT. Cystine was 10-fold higher ( P <.05) in pig hair than in the carcass and HOLT body components. Lysine, histidine, methionine, tryptophan, and phenylalanine concentrations were lower ( P <.05) in

4 516 MAHAN AND SHIELDS Table 2. Nonessential amino acid composition of body component of pigs from 8 to 145 kg body weight (g/100 g protein) Amino acid and Live wt, kg: body components Empty body wt, kg: Avg SEM Ala Carcass HOLT a Asp Carcass HOLT Cys Carcass HOLT Glu Carcass HOLT b Gly Carcass HOLT Hpr Carcass HOLT Pro Carcass HOLT Ser Carcass HOLT Tyr Carcass HOLT Total Carcass HOLT a HOLT = head, internal organs, forelegs, and body trim. b Significant response ( P <.01) between the carcass and HOLT. pig hair than in the carcass and HOLT, but valine and threonine were higher ( P <.05). Because hair and blood contain and retain amino acids, they are important tissues for use in analyzing the amino acid composition of the whole body, and in subsequently estimating the pig s total amino acid requirement at various stages of growth. Multiplication of the protein content of each body component (Table 4) by the relative amino acid composition of the four body components (Table 3) should reflect the body amino acid composition of the whole pig. The relative contribution in weight of the carcass component to the whole body from 8.5 to 145 kg BW increased from 66 to 77% on a whole-body protein basis, whereas the HOLT component decreased from 28 to 15% (Table 4). Consequently, those essential amino acids needed for carcass muscle are required at a higher dietary concentration as the rate of muscle mass increases, whereas those needed for the noncarcass proteins decline with increasing pig weight. The calculated whole-body amino acid composition, expressed on a grams/100 grams of protein basis, from birth to 145 kg BW is presented in Table 5. Many of the amino acids responded in a cubic manner ( P <.05) as pig weight increased. Most of the essential amino acids, except tryptophan, increased from birth to weaning (8.5 kg BW) and then generally reached a plateau to 145 kg BW. Tryptophan was highest in the neonates but declined by 8.5 kg and reached a plateau at 145 kg BW. The reason for its initially higher concentration in the neonates is unclear. Generally, the individual nonessential amino acids in the neonates were similar to those of the 8.5-kg pigs and the overall average (Table 5). The sums of the essential and the nonessential amino acids at each weight increment are reported in Table 5. The essential amino acids increased from birth to 8.5 kg BW and then reached a plateau at 145 kg, whereas the nonessential amino acid were similar from birth to 145 kg BW. The nonessential amino acids generally had a 1.25-fold higher concentration in the whole body than the essential amino acids at each weight interval and were generally parallel to each other (Figure 1). Approximately 92% of the amino

5 PIG AMINO ACID COMPOSITION 517 Table 3. Relative composition of essential and nonessential amino acids in various body components of pigs (g/100 g protein) Amino acid Carcass SE Head, legs, organs, trim SE Whole blood SE Hair SE No. of observations Essential amino acids Arg 6.5 a a b a.02 His 3.7 a a b c.02 Ile 3.9 a a b a.02 Leu 7.1 a a b a.07 Lys 7.6 a b c d.12 Met 1.9 a a.1.8 b.02.5 b.05 (Met + Cys) 3.0 a a b c.29 Phe 3.8 ad a c d.05 (Phe + Tyr) 6.8 a a b a.04 Thr 4.0 a a a b.10 Trp 1.1 a a a.03.3 b.03 Val 4.7 a a b c.08 Nonessential amino acids Ala 6.6 a a b c.04 Asp 8.9 a a b c.05 Cys 1.1 a a a b.28 Glu 13.7 a b c a.12 Gly 9.1 a a b b.32 Hpr 3.0 a a.4.1 b.01.1 b.01 Pro 6.2 a a b a.12 Ser 3.9 a ab b c.11 Tyr 3.0 a a a a.03 a,b,c,d Means within a row with different superscripts differ ( P <.05). acids (essential and nonessential) were recovered from the neonates, whereas close to 100% were accounted for with the heavier pigs. This implies that nonprotein fractions may be present in the developing fetus during late gestation and at birth in the young pig. Dickerson and Widdowson (1960) had also reported that nonprotein N was higher in neonatal pigs than in pigs either 4 to 6 wk of age or in adults. The relative amount of total body lysine (g/100 g protein) increased from birth to approximately 37 kg BW and reached a plateau at 145 kg BW ( P <.05). The increasing lysine content in growing pigs is attributed to its higher concentration in the carcass and in whole blood. The other essential amino acids, except tryptophan, increased to 8.5 kg BW and generally reached a plateau at 145 kg BW. These results support the concept of higher dietary lysine requirement, and perhaps other amino acids, during the period of rapid muscle growth relative to the other essential amino acids. Munks et al. (1945) had reported a higher arginine, histidine, lysine, and threonine content in chicken muscle than in egg protein, suggesting a higher dietary requirement for these amino acids during the period of muscle formation. Discussion Figure 1. Quantitative relationship of essential ( ) and nonessential ( ) amino acids in pigs from birth to 145 kg body weight. Each body protein has its individual specific amino acid composition, turnover rate, and maintenance need, and the rate and priority of development of each proteinaceous tissue also varies with the other body tissues as the animal grows. The amino acid composition of the whole body thus reflects the accumulated

6 518 MAHAN AND SHIELDS Table 4. Quantity of protein in various body components Weight, kg Body components No. of Empty Head, legs, Whole pigs Live body Carcass organs, trim Blood Hair Total Protein content, kg total quantity of amino acids retained in all body components to a particular stage of development but does not reflect the transfer between and within the various proteinaceous tissues or the pig s maintenance needs. Our data suggest that because of the high cystine content in pig hair, the requirement for the sulfur amino acids is higher for maintenance, a conclusion also reported by Baker (1997). In our study, the pattern of amino acids in the carcass was similar between 8.5 and 145 kg BW, with carcass lysine, histidine, arginine, methionine, threonine, and isoleucine concentrations generally higher than the HOLT body components. Other studies have, however, reported similar or lower lysine contents in the carcass than in whole body lysine values (Bikker et al., 1994; Hahn and Baker, 1995). Our results Table 5. Amino acid composition of whole pigs from birth to 145 kg body weight (g/100 g protein) Amino Live wt, kg: acid Empty body wt, kg: Avg a SEM Essential amino acids Arg c His d Ile c Leu c Lys d Met (Met + Cys) c Phe (Phe + Tyr) Thr Trp d Val c Total b c Nonessential amino acids Ala Asp d Cys Glu d Gly c Hpr c Pro c Ser c Tyr c Total a The average and SEM values excludes the data from 1.5-kg neonatal pigs. b Total excludes (Met + Cys) and (Phe + Tyr) values. c Cubic response ( P <.05). d Quadratic response ( P <.05).

7 PIG AMINO ACID COMPOSITION 519 suggest, however, that lean genotypes may have a higher dietary requirement for these six amino acids relative to the other essential amino acids during the period of rapid muscle growth. Jelić (1977), Madsen and Mortensen (1979), and Dueé et al. (1980) had previously reported that the lysine concentration in muscle protein averaged 8.9 g/100 g muscle protein, whereas Edmunds et al. (1979) had reported a value of 6.0 g/100 g muscle protein. Kyriazakis et al. (1993) had demonstrated higher lysine and histidine concentrations with increasing body protein. The results of Campbell et al. (1988) and Bikker et al. (1994) suggests that as muscle accretion increases, energy can become a limiting factor for muscle formation. Dietary arginine, histidine, and isoleucine are generally at substantially higher concentrations in most swine dietary protein mixtures relative to the pig s requirement for these amino acids. In contrast, because dietary lysine, threonine, tryptophan, and methionine concentrations are provided at concentrations closer to the pig s requirement in most cereal grain-oilseed mixtures, they are more likely to be limiting. The results of Hahn and Baker (1995) demonstrated increased N retention and carcass protein when finisher pigs of a lean genotype were fed diets that contained higher concentrations of methionine, threonine, and tryptophan when the lysine requirement had been met. The requirements for these three amino acids were therefore higher for older than for younger pigs. These authors attributed the response to the higher maintenance need for these amino acids. Our results suggest that at least part of this response may also have been due to the higher dietary requirement for these amino acids from the higher deposition of carcass protein as pigs get older. Although sex can affect the quantity of protein deposited, differences in whole-body amino acid composition (g/100 g protein) have not been demonstrated between boars and gilts (Siebrits et al., 1986; Kemm et al., 1990) or between pigs of a lean or fatter genotype (Dueé et al., 1980; Siebrits et al., 1986). The results from several studies (Dueé, 1980; Siebrits et Table 6. Comparison of whole-body essential amino acid composition of pigs from literature sources Bikker Kyriazakis Chung Kemm Batterham Campbell Moughan Siebrits Amino This et al. et al. and Baker et al. et al. et al. and Smith et al. acid report a (1994) b (1993) c (1992) d (1990) e (1990) f (1988) g (1987) h (1986) i Avg g/100 g protein Arg NR NR NR 6.5 His Ile Leu Lys Met NR 1.9 (Met + Cys) NR 3.1 Phe (Phe + Tyr) Thr Trp 1.1 NR.8.8 NR NR.8.7 NR.8 Val Ratio to Lys Arg NR NR NR 1.00 His Ise Leu Met NR (Met + Cys) NR Phe (Phe + Tyr) Thr Trp.15 NR NR NR NR.13 Val NR = not reported. a A total of 71 barrows and female pigs were used that weighed from 8.5 to 145 kg body weight. b A total of 95 female pigs were used that weighed from 20 to 45 kg body weight. c A total of 75 male and female pigs were used that weighed 32 kg body weight. d A total of 20 pigs were used that weighed from 10 to 20 kg body weight. e A total of 72 male and female pigs were used that weighed 20, 30, or 90 kg body weight. f A total of 16 male and female pigs were used that weighed 20 and 45 kg body weight. g A total of 43 male pigs that weighed 8 and 20 kg body weight. h A total of 20 male pigs that weighed 20 and 45 kg body weight. i A total of 100 male and female pigs were used that weighed 30 to 110 kg body weight.

8 520 al., 1986; Kemm et al., 1990; Kyriazakis et al., 1993) have indicated that whole-body amino acid composition was similar over a wide weight range. Dietary protein level was also found to have no influence on the relative amino acid composition (Kemm et al., 1990). Although the relative composition of amino acids (g/100 g protein basis) may be similar in the pig, the scientific literature abounds with evidence that the quantity of protein and thus the quantity of individual amino acids required and their deposition is influenced by sex, genotype, dietary protein level, and pig age. It would therefore seem that the greatest determinant in estimating the dietary amino acid requirement for pigs is an accurate estimate of the quantity of total protein deposited at each production stage, and then to determine the lysine requirement with the other amino acids in slight excess. The ratio of amino acids from body composition studies in relation to the lysine requirement, with an adjustment for maintenance requirement, has been used to establish the ideal protein concept and the dietary essential amino acid needs of pigs (Baker, 1997). These ratios can only be considered as estimates because tissue turnover rates and maintenance needs are not accurately known. Hahn and Baker (1995) subsequently determined that threonine, methionine, and tryptophan were needed at a higher ratio to lysine in older than in younger pigs. This suggests that the ratio and ideal protein (amino acid) profile may differ with pig weight. Our results also suggest that with increasing deposition of carcass protein and a declining noncarcass protein component the ideal ratio may change with pig weight, age, and most probably genotype. When the results of several body compositional studies are compared, a wide difference exists between the relative (g/100 g protein basis) amino acid compositions (Table 6). The subsequent results demonstrated that the whole-body lysine concentration varied by approximately 14% (average 6.4 g/100 g protein), suggesting that analytical differences between laboratories for amino acids, protein, and animals occur. This could be attributable to differences in sample homogeneity, incomplete hydrolysis of body proteins, or other differences in analytical methodology. The relative ranking between the amino acids was, however, generally similar within each study. When the amino acids were compared on a ratio basis (using lysine as the reference), there still remained a wide discrepancy between laboratories, but the data range seemed to be somewhat closer for most amino acids. The combined results from these studies and our experiment suggest that because 1) amino acid composition analyses differ between laboratories, 2) tissue turnover rates of amino acids are unknown, 3) the priority of tissue development may differ with MAHAN AND SHIELDS different growth rates at different body weights and perhaps with different genotypes, and 4) the maintenance needs of pigs are not known at the various ages or body weights, the use of computer modeling to determine amino acid requirements is subject to much error until these variables can be more accurately assessed. If muscle tissue requires more lysine, and perhaps more methionine, threonine, and tryptophan, than other tissues, then pigs that have higher rate of development of this tissue would not only have a higher dietary requirement for these amino acids, but their dietary amino acid ratios may differ from those of pigs of a fatter genotype. Body amino acid composition data, however, provide a desirable starting point from which the ratio of body amino acids can be used to estimate the dietary level that should be initially evaluated when determining the dietary amino acid requirement levels. Implications Amino acid composition of pig carcasses and the other noncarcass components was similar within each component from weaning to 145 kg body weight. The sum of the essential amino acid concentrations in the carcass was approximately 10% greater than the sum of the essential amino acids in the composite of the head, internal organs, and forelegs. Consequently, when muscle accretion increases, the necessary dietary lysine level, and perhaps that of methionine, threonine, and tryptophan, may be higher than that of other essential amino acids. Comparing whole-body amino acid compositions from several scientific studies showed a wide difference in the relative concentrations between studies. Literature Cited AOAC Official Methods of Analysis (13th Ed.). Association of Official Analytical Chemists, Washington, DC. ARC The Nutrient Requirements of Pigs. Agricultural Research Council, Commonwealth Agricultural Bureaux, Slough, U.K. Baker, D. H Ideal amino acid profile for swine and poultry and their application in feed formulation. Biokyowa Tech. Rev. No. 9. pp Batterham, E. S., L. H. Anderson, D. R. Baigent, and E. White Utilization of ideal digestible amino acids by growing pigs: Effect of dietary lysine concentration on efficiency on lysine retention. Br. J. Nutr. 64: Bikker, P., M.W.A. Vergstegen, and M. W. Bosch Amino acid composition of growing pigs is affected by protein and energy intake. J. Nutr. 124: Campbell, R. G., M. R. Taverner, and C. J. Rayner The tissue and dietary protein and amino acid requirement of pigs from 8 to 20 kg live weight. Anim. Prod. 46: Chung, T. K., and D. H. Baker Efficacy of dietary methionine utilization by young pigs. J. Nutr. 122: Cole, D.J.A The amino acid requirement of pigs. The concept of an ideal protein. Pig News Info. 1:

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