USE OF THE IDEAL PROTEIN CONCEPT FOR PRECISION FORMULATION OF AMINO ACID LEVELS IN BROILER DIETS'

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1 61997 Applied Poultry Science, Inr USE OF THE IDEAL PROTEIN CONCEPT FOR PRECISION FORMULATION OF AMINO ACID LEVELS IN BROILER DIETS' JASON L. EMMER? Department of PouItry Science, POSCBuilding, 1260 West MapIe Street, University of Arkansas, Fayetteville, AR Phone: (50I) FM: (501) DAWD H. BAKER Department of Animal Sciences, Universiv of Illinois, Urbana, IL Primary Audience: Nutritionists, Research Scientists, Veterinarians DESCRIPTION OF PROBLEM Sophisticated computer feed formulation programs have made precision nutrition a realistic goal. Such programs can assess numerous parameters, including nutritive quality of feed and feed ingredients and economic factors. Growing concerns about the environmental impact of animal production may lead to the addition of environmental factors such as nitrogen and phosphorus pollution as parameters in feed formulation schemes in the future. Because it provides a precise ratio of amino acids andminimizes nitrogen excretion, the ideal protein concept can play an integral role in precision nutrition, particularly as nontraditional protein-containing ingredients become increasingly available. ILLINOIS IDEAL CHICK PROTEIN Illinois Ideal Chick Protein (IICP) is based on a concept developed by H. H. Mitchell and H. M. Scott at the University of Illinois in the late 1950s and early 1960s. The 1 Presented at the 1997 Poultry Science Association Informal Poultry Nutrition Symposium: "Precision Nubition for Poultry. " 2 To whom correspondence should be addressed

2 ~ ~~ EMMERT and BAKER Symposium 4.63 basic goal is to provide a blend of indispensable amino acids that exactly meets an animal's requirement for protein accretion and maintenance, with no deficiencies and no excesses. The ideal protein concept uses lysine as a reference amino acid, with the requirements for all other indispensable amino acids expressed as a percentage of lysine. Lysine was chosen as a reference amino acid for several reasons: 1) in practical broiler diets, lysine is the second-limiting amino acid after SAA, and lysine supplementation is economically feasible, 2) lysine analysis in feedstuffs is straightforward, 3) dietary lysine is used only for protein accretion and maintenance (i.e., it has no precursor role), and 4) lysine requirement data for a variety of dietary, environmental, and body compositional circumstances are readily available. Table 1 shows a portion of the IICP profile, including those amino acids typically considered most important in practical broiler diets (lysine, SAA, threonine, valine, arginine). For further information regarding the development of IICP, see Baker and Han [l] and Baker [2]. The use of lysine as a reference amino acid is one of the most beneficial aspects of IICP, because solid requirement data are not available for most amino acids, especially beyond 21 days of age and under varying dietary and environmental conditions. Therefore, it makes sense to use the large body of literature to set ideal ratios of each essential amino acid to lysine rather than attempt to determine individual requirements under every conceivable condition. Use of IICP allows for easy formu- lation of diets 1) for males or females, 2) high or low in metabolizable energy or crude protein, 3) fed to strains with high or low lean growth potential, and 4) fed under different environmental conditions. In addition, it minimizes nitrogen pollution and prevents overor under-fortification of diets with amino acids. The nature of IICP requires that some important issues be considered. First, the lysine requirement is very important, because it is the basis for setting requirements for all other indispensable amino acids. Consideration of amino acid digestibility is also very important. All of the ideal ratios are based on digestible levels of dietary amino acids. Using this basis eliminates differences in absorption and utilization from various sources. In a cornsoybean meal diet, use of total vs. digestible amino acid levels is of less significance, due to the similarity in digestibility values among indispensable amino acids of importance in this type of diet [3]. However, even in this case, use of digestible amino acid levels is recommended, particularly if crystalline amino acids are being used. For example, if a particular corn-soybean meal diet requires a total level of 1.26% lysine for maximal performance (equivalent to 1.12% digestible lysine, based on a digestibility of 89% [3]), one could formulate the diet to contain 1.26% total lysine from corn and soybean meal. Alternatively, a portion of the lysine requirement could be fulfilled with crystalline lysine, which is 100% digestible. If the diet was formulated on a total basis, and contained 1.00% lysine from corn TABLE 1. Universitv of Illinois ideal ratios for selected amino acids at three growth periods AMINO ACID^ OTO 21 DAY? 21 TO 42 DAYS^ 42 TO 56 DAYS' IDEAL RATIO IDEAL RATIO IDEAL RATIO 70 of Lysine % of Lysine 70 of Lysine Lysine Methionine + Cystine Methionine Cystine Threonine Valine Arginine 1M)

3 464 IDEAL PROTEIN CONCEPT and soybean meal, 0.26% crystalline lysine would be required. However, this would result in a digestible lysine content of 1.15% (1.00 x 89% x 100%), which exceeds the digestible lysine requirement. Use of digestible amino acid levels is advisable to avoid over-fortification when using crystalline amino acids. In addition, future use of alternative protein sources, such as rendered animal meals, will likely require diet formulation on a digestible basis, as amino acid digestibility values of alternative ingredients will likely differ substantially from those of corn and soybean meal. IICP offers an advantage here by allowing for incorporation of alternative ingredients without requiring the determination of total amino acid requirements for these diets. PREDICTION OF REQUIREMENTS In addition to the benefits of using ideal ratios to formulate amino acid levels during the early growth period (0 to 3 wk), IICP can be beneficial in predicting amino acid requirements at later stages, during which accurate requirement information for most amino acids is lacking. Recently, discrepancies among the rates of decrease in the requirement for lysine, SAA, and threonine as chicks age from 0 to 8 wk prompted an examination of the threonine requirement at the later growth stages. As illustrated in Figure 1, the requirement for digestible lysine and SAA (shown here for mixed sex populations) decreases by approximately 30%, whereas the threonine requirement, as listed by the NRC [4], decreases by only 16%. Specifically, for Day 11, requirement values were: lysine, 1.07% [5]; sulfur amino acids, 0.7 7% [4]; threonine, 0.70% [4]; for Day 32 lysine, 0.865% [6]; sulfur amino acids, 0.62% [7]; threonine, 0.64% [4]; and for Day 49: lysine, 0.745% [4]; sulfur amino acids, 0.54% (estimated based on ideal ratios); threonine, 0.59% [4]. Use of IICP ratios yields threonine requirements that are lower than those listed by the NRC [4] and more in agreement with the expected decrease over the three growth periods (Table 2). To confirm the accuracy of threonine requirements predicted by IICP ratios, Webel et al. [8] conducted experiments to assess the threonine requirement for male Ross x Hubbard chicks during the 21 to 42 and 42 to 56 day growth periods. These chicks were found to require 0.61 and 0.52% digestible threonine to maximize weight gain and feed - = Lysine Sulfur amino acids \ Threonine AA reqt. (%) of diet) 0.7- FIGURE 1. Comparison of NRC [4] estimates of the decreasing threonine requirements in broilersfrom hatching to 49 days relative to best estimates of the decreasing lysine and SAA requirements during the same growth periods

4 EMMERT and BAKER Symposium 465 Day 21 to to 56 Decrease, %E DlGESIlBLE IDEAL DIGESTIBLE TOTAL LYSINE THREONINE THREONINE THREONINE REQUIREMENT RATIO REQUIREMENT REQUIREMENTB %of Diet % of Lysine % of Diet % of Diet 0.89' D efficiency during the 21 to 42 and 42 to 56 day growth periods, respectively. Comparison of determined and predicted requirements (Table 3) indicates that IICP ratios allowed for a very close approximation of the determined threonine requirements during later growth stages. Replacing NRC [4] threonine requirements with those determined by Webel et al. [SI leads to a percentage decrease of 27% from Day 0 to Day 56 in a mixed-sex population (Figure 2), which is in much closer agreement with the decrease in lysine and SAA requirements over thk same time period. Specifically, for Day 11, requirement values were: lysine, 1.07% [5]; sulfur amino acids, 0.77% [4]; threonine, 0.70% [4]; for Day 32: lysine, 0.865% [6]; sulfur amino acids, 0.62% [7]; threonine, 0.593% [ti]; for Day 49 lysine, 0.745% [4]; sulfur amino acids, 0.54% (estimated based on ideal ratios); threonine, 0.51% [8]. This offers further evidence that IICP can play an important role in predicting amino acid requirements, even at later stages of growth. PARTITIONING LYSINE AND THREONINE REQUIREMENTS During the development of IICP, it was assumed that the ideal ratios of certain amino acids (cystine, threonine, tryptophan, valine, arginine, isoleucine) would likely increase as a percentage of lysine during the periods 21 to 42 and 42 to 56 days. This was assumed primarily because it seemed probable that as buds age maintenance needs for these amino acids would increase faster than maintenance needs for lysine. Maintenance needs as a percentage of total amino acid requirements are minimal (probably 3 to 6%) for young birds, but they increase substantially as birds advance in age and weight. However, research using pigs and rats has long led to the belief that the percentage of lysine required for maintenance is very small and does not increase substantially as birds grow and age. Thus the ideal ratios of those amino acids TABLE 3. Comparison of the predicted and determined digestible and total threonine requirements at two growth periods PREDICTED THREONINE REQUIREMENT DETERMINED THREONINE REQUIREME& Dieestible TotalB Dieestible TotalB Day % of Diet 70 of Diet Yo of Diet 70 of Diet 21 to to

5 466 JAPR IDEAL PROTEIN CONCEPT Lysine - Sulfur amino acids - Threonine Digestible AA reqt. (%) of diet) contributing significantly to maintenance apparently increase with birds age. Recent studies with threonine [8, 91 have evaluated the percentage of the total requirement needed for maintenance during three growth periods (0 to 21, 21 to 42, and 42 to 56 days) by partitioning the total requirement into maintenance and accretion components. Threonine accretion and protein accretion have been evaluated, with both criteria leading to similar estimates of maintenance as a percentage of the total requirement (Table 4). As expected, the percentage of the total requirement needed for maintenance increased as the TABLE 4. Partitioning the digestible threonine requirement (mg/da~/kg. ~) into maintenance and accretion :omponents based on whole-body accretion studies rotala THREONINE REQUIREMENT Maintenance (based on zero threonine accretion)b Protein accretion Maintenance, Yo of total rotala Maintenance (based on B zero protein accretion) Protein accretion Maintenance, Yo of total 0 to 21 Days 21 to 42 Days 42 to 56 Days 718 I Obtained bv subtracting the maintenance requirement from the total requirement.

6 Symposium EMMERT and BAKER 467 chicks aged. Similar studies have been conducted with lysine [lo], which also appears to exhibit a substantial increase in maintenance as a percentage of the total requirement (Table 5). However, a sizable difference occurred depending on whether lysine or protein accretion was the response criterion. In agreement with previous research [2, 111, use of protein accretion led to very low estimates of maintenance as a percentage of the total requirement, regardless of the particular growth period. In contrast, use of lysine accretion as a parameter led to much larger estimates of maintenance as a percentage of lysine. This suggests that lysine needs for maintenance may be substantially higher than previously thought, and thus similar in magnitude to needs for other amino acids known to be important contributors to maintenance. REEVALUATION OF IDEAL RATIOS DURING LATER GROWTH STAGES Our recent broiler studies regarding threonine [8] and SAA [I requirements, and threonine and lysine needs for maintenance [8,9, 101, provide a basis for reevaluating the ideal ratios of these amino acids during the periods 21 to 42 and 42 to 56 days posthatching. Included in Table 6 are best estimates of the digestible lysine, threonine, and SAA requirements for the periods 21 to 42 and 42 to 56 days, with all values adjusted for mixed-sex feeding (male broiler chicks have higher amino acid requirements than females [5,6]). The sole exception is the 42- to 56-day requirement for SAA, which was estimated based on an assumed ideal ratio for SAA:lysine of 72% during the 21 to 42 day growth period. For SAA and threonine, new ratios have been calculated (Table 6) relative to the listed lysine requirements, and in each instance the calculated ratio is less than the ratio previously assumed (Table 1) in the IICP profile for birds beyond 21 days of age. Specifically, the ratio of threonine to lysine in the IICP profile had been assumed to increase from 67% during the 0 to 21 day growth period to 70% during the two later growth periods. Calculation of the threonine:lysine ratio using the values listed in Table 6 leads to a value of 68.5% for both later growth periods. This agrees with recent threonine requirement data of Kidd et al. [12]. The ratio of SAA to lysine in the IICP profile had been assumed to increase from 72% during the 0 to 21 day growth period to 75% during the two later growth periods. Calculation of the SAA ratio using the values listed in Table 6 leads to a value of 72% for both later growth periods. The apparent disagreement for older chicks between values listed in Table 6 and those in the IICP profile (Table 1) has several implications. As previously discussed, recent data indicate that the lysine requirement for TABLE 5. Partitioning the digestible lysine requirement (mg/da~/kg. ~) into maintenance and accretion

7 468 JAPR IDEAL PROTEIN CONCEPT TABLE 6. Calculated ideal ratios of threonine and SAA to lysine for broiler chicks during later growth periodsa Day 21 to 42 DIGFSIIBLE DlGESLlBLE PROPOSED DIGESIlBLE PROPOSED LYSINE THREONINE THREoNpE SAA SAA REQUIREMENP REQUIREMEN~ RATIO REQUIRE ME^ unod %of Diet 70 of Diet % of Lysine 70 of Diet to maintenance may be substantially greater than previously thought, suggesting that increasing the ratios of amino acids considered important for maintenance (namely SAA, threonine, and tryptophan) may not be appropriate. In the growing pig, the ideal ratios (relative to lysine) of threonine, SAA, and tryptophan for maintenanceper se are much higher than the ideal ratios for protein accretion per se [2, 111. It seemed a logical assumption that the same relationships would exist in growing broilers, but our recent evidence would suggest otherwise. The IICP ratios for the growth periods 21 to 42 and 42 to 56 days had been estimated based on assumptions and data [l] from the 0 to 21 day growth period. Further research is needed to empirically test ratios for later growth periods and to evaluate the lysine requirement for maintenance at all stages of growth. PREDICTION OF WEEKLY AMINO ACID REQUIREMENTS The potential exists to use digestible amino acid requirements for 0 to 21,21 to 42, and 42 to 56 day growth periods to predict requirements for narrower ranges of the growth curve. By generating regression equations using digestible requirements for known time periods, one can predict the requirement for specific amino acids at any point during growth. As an example, data for digestible lysine, SAA, and threonine requirements in Figure 2 have been used to generate linear regression equations for predicting digestible requirements for these amino acids at eight 1-wk intervals from 0 to 56 days of age. The regression equations and the resulting re- quirements are listed in Table 7. It should be noted that these requirements have not been validated with animal experiments. Rather, the example is intended to illustrate the potential for precisely estimating requirements over narrow age ranges. Requirements for narrow age ranges could be used in a phase-feeding scheme in which feed formulations are changed as frequently as is economically and physically feasible, be it weekly, semi-weekly, etc. Comparison of an eight-phase feeding scheme with a three-phase scheme reveals several important points. First, the three-phase scheme could result in under-fortification during the early portion of each growth period, and overfortification during the later portion of each growth period. Obviously, either scenario is undesirable whether due to poorer performance or cost inefficiency. Assuming equal feed intakes and growth performance, the feeding scheme involving eight diet changes could result in slightly lower intakes of undigested indispensable amino acids and nitrogen (data not shown), which could lead to less nitrogen output in excreta. However, the differences could be more substantial if the 8-wk scheme led to a more efficient use of feed or a decrease in the time required to reach a desired market weight, which could also lead to a significant economic savings. Empirical testing of schemes such as 8-wk phase feeding vs. more traditional feeding schemes is warranted, both to ascertain the validity of requirements determined with regression equations, and to evaluate the potential economic and environmental impact of such feeding.

8 EMMERT and BAKER Symposium 469 Day 0 to 7 14 to to to to to to 56 LYSINE W QUIREME~ SAA REQUIREMENTB THREONINE REQUIREMENT^ Digestible TotalD Digestible TotalE Digestible TotalF %of Diet % of Diet %of Diet % of Diet % of Diet % of Diet to 14 I 1.10 I 1.23 I I CONCLUSIONS AND APPLICATIONS 1. The IICP concept directly fits into the concept of precision nutrition for poultry. By setting amino acid requirements using ratios to lysine, and by adhering to use of digestible amino acid levels, the IICP concept eliminates over- and under-fortification of diets with amino acids of importance, in addition to lowering nitrogen excretion. 2. Accurate requirement estimates for amino acids other than lysine can be determined for later growth periods using IICF', but it is appropriate to confirm estimates for older birds with empirical data. 3. Recent data suggest that the lysine requirement for maintenance may be substantially greater than previously thought, bringing into question the validity of increasing the ratio of amino acids to lysine during later growth periods. New ratios for sulfur amino acids and threonine have been calculated for the 21 to 42 and 42 to 56 day growth periods, and these ratios are lower than those previously listed for IICF! 1. Baker, D.H. and Y. Han, Ideal amino acid profile for broiler chicks during the first three weeks posthatching. Poultry Sci Baker, D.H., Ideal amino acid profiles for swine and poultry and their application in feed formulation. BioKyowa Tech. Rev. 9:l Parsons, C.M., Amino acid digestibilities for poultry: Feedstuff evaluation and requirements. BioKyowa Tech. Rev. 1:l-15. REFERENCES AND NOTES 4. National Research Council, Nutrient Requirements of Poultry. 9th Rev. Edition. Natl. Acad. Press, Washington, DC. 5. Han, Y. and D.H. Baker, Effects of sex, heat stress, bodyweight, and genetic strain on the dietary I ine requirement of broiler chicks. Poultry Sci $8. 6. Ha4 Y. and D.H. Baker, Digestible lysine reouirement of male and female broilerchicks during the eked three to six weeks posthatching. Poultry-Sci. I!3:

9 470 IDEAL PROTEIN CONCEPT 7. Baker, D.H., S.R Fernandez, D.M. Webel, and C.M. Parsons, 19%. Sulfur amino acid requirement and cystine replacement value of broiler chicks during the period three to six weeks posthatching. Poultry Sci. 75: Webel, D.M, S.R Fernandez, C.M. Parsons, and D.H. Baker, Digestible threonine requirement of broiler chickens during the period three to six and six to eight weeks posthatching. Poultry Sci Edwards, H.M., 111, D.H. Baker, S.R Fernandez, and C.M. Parsons, Maintenance threonine requirement and efficiency of its use for accretion of whole-body threonine and protein in young chicks. Br. J. Nutr. 78: Edwards, H.M., 111, S.R. Fernandeg C.M. Parsons, and D.H. Baker, Maintenance lysine and threonine requirements of young chicks and efficiency of their utilization above maintenance. Poultry SCI. 75(Suppl): Fuller, M.F., Amino acid requirements for maintenance, body protein accretion, and reproduction in pigs. Pages in: Amino Acids in Farm Animal Nutrition. J.P.F. D Mello, ed. CAB Intl., Wellingford, Oxon, UK. 12. Kidd, M.T., B.J. Ken, and N.B. Anthony, DietaIy interactions between lysine and threonine in broilers. Poultry Sci. 76:60&614.