MODELLING FOR PRECISION NUTRITION^

Transcription

1 81997 Applied Poultry Science, Inc MODELLING FOR PRECISION NUTRITION^ GENE M. PESTI~ Department of Poultry Science, The University of Geolgia, Athens, GA Phone: (706) FM: (706) BILL R. MILLER Department of Agricultural and Applied Economics, The Univerrity of Georgia, Athens, GA Primary Audience: Nutritionists, Managers INTRODUCTION Bolden [l] outlined the changing emphases in poultry nutrition in the United States during the last four decades. In the 1960s the emphasis was on improving the growth rate of broilers; in the 1970s feed conversion ratio was emphasized; in the 1980s feed costfive weight became of primary importance; and now, in the late 199Os, feed cost/meat yield is of primary importance. During the same period of time, however, the model for feed formulation has remained essentially the same. Least-cost Linear programming feed formulation models that were applied in the 1960s are still being used in the late 1990s in exactly the same fashion. Experience has led more to refinements in specifications than to any development in techniques. LEASTCOST FEED FORMIJUTION The typical formulation model for poultry feed used today simply calculates the combination of ingredients that meet given specifications at the least cost [2]. Maximum performance of feed is an implied least-cost goal, yet there is no formal consideration of whether the given spc:cifications yield maximum performance. Maximum technical performance, however, does not necessarily yield maximum profits. Formulating feed usually involves specifying nutrient minimums per unit, and most software allows the spedication of ratios between nutrients as well. This model is assumed to result in maximum profits (through least-cost ration discovery), based on the belief that birds will eat the correct amount of nutrients as long as feed ingredients 1 Presented at the 1997 Poultry Science Association Informal Poultry Nutrition Symposium: "Precision Nutrition for Poultry. " 2 To whom correspondence should be addressed

2 484 JAPR ECONOMICAL NUTRITION MODELLING provide the right proportion of metabolizable energy. ECONOMIC FEEDING THEORY In 1953 HJ. Almquist [3] outlined wellknown economic principles that should be applied to feed formulation. In a paper addressing application of the law of diminishing returns in determining feed nutrient content, he explained, "The principles described are not new, but have been employed only rarely by workers in nutrition." Economists refer to these principles as static economic theory because the role of time is not explicit. Modem application of profit maximization theory includes time, or age of the chicken, as an important variable. Figure 1 shows a typical diminishing response curve that is expected from feeding broiler chickens and has been validated in experiments [3]. This curve is for one specific fmed technology of stock, housing type, etc., but with feed intake at various levels. The curve shows that broiler body weight increases at a decreasing rate with respect to feed intake. The body weight and feed intake axes are cor- related with bird age, although the relationships are not necessarily linear. An important measure of performance most often used by biologists is ONAB. This ratio defines feed conversion and is depicted as two linear segments. Marginal physical product (MPP, g gained/g feed intake) is depicted as the slope of the curve at three points to illustrate the diminishing returns phenomenon. The slopes decrease with feed intake, as shown in Figure 1; the values of the slopes are plotted on the MPP he in Figure 2. Multiplying MPP by the price of broilers produces the value of marginal product (VMP) curve, which describes the added dollar value of broiler meat expected from each additional unit of feed intake. Comparing the dollar value of an added unit of feed to the VMP curve determines the point of maximum economic efficiency. Basic economic logic holds that producers should be willing to continue investing in feed intake as long as the added value of broiler meat produced is greater than the added cost of feed required for production. When added feed cost becomes equal to added broiler meat value (VMP line intersects MPP, 2.E! n d 2. $4 4 I Feed Conversion Ratio as a Measure of Efficiency 1

3 Symposium PESTI and MILLER 485 Value of Marginal Product / Feed = Price x MPP Price of Feed Feed Intlake (-Age) FIGURE 2. The use of the marginal physical product (MPP) of feed in determining the most profitable level of feed intake; the scale for the Value of Marginal Product is not shown price, Figure 2) the birds should be slaughtered, before costs exceed returns. Applying value of returns/cost logic to Figure 2 will show that profit increases up to a certain feed intake, beyond which profits decrease (Figure 3). Industrial planning for profit requires some method of determining the feed intake and nutrient levels that will result in maximum profit (Figure 3). More importantly, if the feed intake that maximizes profit per bird per unit of time is known, then the goal of producers should be to maximize technical feed efficiency (minimize the feed conversion ratio) as illustrated in Figure 1, where ONOB is smaller than ONOC. Leastcost feed formulation models lower the price of feed (Figure 2) and are adequate for profit maximization only if the feed intake and nutrient levels that result in maximum feed efficiency are already known. The relationships illustrated in Figures 2 and 3 as related to the size of the bird may be used to determine the point of maximum economic profit (Figure 4). The point of maximum economic profit will not necessarily reflect minimum feed conversion ratio over all ages and body weights; it may in fact be achieved with diets that yield less than maximum growth rates (MPP) and maximum feed efficiency (ONOB). Distinguishing between maximum economic performance and maximum technical performance is important to understanding the difference between least cost and maximum profit feed formulation models. FORMULATION THEORY To understand why formulation models have not changed, an e:xplicit understanding of the underlying nutritional assumptions is necessary. Information iri the National Research Council Nutrient Requirements of Poultry Series has reflected prevailing formulation theories. From the 19r34 NRC [4]: "Birds tend to eat to satisfy their energy requirements if fed free choice"; "It is impossible to set an energy requirement in terms of kilocalories per kilogram of diet because birds adjust their feed intake to obtain the necessary daily requirement of energy"; "Consequently it is possible within limits to regulate the intake of all nutrients, except water, by including them in the diet in specific ratios to available energy." In 1994, however, the NRC [5] said: "Because

4 486 JAPR ECONOMICAL NUTRITION MODELLING Feed Intake (-&e) FIGURE 3. Theoretical representation of broiler production profitability as a function of feed intake and resultant body weight of the bird Feed Intake (-Age) FIGURE 4. The use of marginal analysis to determine the weight of broiler chicken that maximizes profits the preponderance of data shows that changes in feed intake usually are not proportional to changes in dietary energy concentration, the use of specific proteinlamino acid-to-dietary energy ratios in formulating poultry diets must be carefully evaluated and "It would be desirable to have mathematical models available that would facilitate the selection of most economical combinations of dietary concentrations of proteinlamino acids (and other nutrients) and energy to achieve poultry production goals." M.E. AND FEED INTAKE Perhaps the NRC [4,5] position changed because the data never supported the original hypothesis that birds can adjust feed intake to get just the right amount of energy each day. Such an assumption was convenient for the available feed formulation model, but data obtained did not provide a good fit. The review by Fisher and Wilson [6] clearly demonstrated that although broilers decrease consumption as energy level increases, the decrease is not enough to keep energy intake constant while the birds self-select the correct

5 PEST1 and MILLER Symposium 487 level of nutrients. In fact, as energy level increases, birds grow more, feed efficiency increases, and the birds display a wider range of increases in fat. Producers need a method of choosing the right energy level. DIMINISHING RETURNS TO THE CALORIE-PROTEIN AMINO ACIDS RATIO In the original paper on the calorieprotein ratio (cpr) [A, there was a very poor relationship between growth or feed consumption and the cpr and thus no obvious "optimum" cpr for broiler growth (no r values for the relationship were even given). However, there was an excellent relationship between cpr and various carcass parameters with excellent r values ( > 0.9) presented (although there was still no obvious "optimum" cpr). Carcass composition can be predicted very well from the cpr, but just as well (or better) from individual protein and energy levels. The idea of an optimal calorie-to-protein ratio is very convenient for least-cost hear programming models, but unfortunately the data never did support that hypothesis. Data from experiments conducted around the world with various protein and energy levels (not correlated) were used to compare the cpr model and a model with separate terms for dietary protein and energy levels. The separate terms model provides a much better prediction of both body weight and feed intake (Table 1). This indicates that knowing protein and energy levels of diets may allow the prediction of performance response. Experimental data have shown that trade-offs between protein and energy levels allow different energy-protein ratios to produce the same body weight [7]. Fixing the ratio between dietary protein and mergy levels is without further benefit for predicting efficient feed intake and resulting growth. Baker [8] published the results of an experiment to determine the chick's response to dietary lysine. As suggested by Figure 1, the gain response was sigmoidal in shape (Figure 5). Baker concluded, "A plot of gaidg lysine intake against dietary lysine concentration for the crjstalline lysine series indicates that lysine is not equally utilized at all dietary concentiations" (as plotted in Figure 6). Calculation of the MPP curve (the marginal gain curve, Figure 7) from Baker's data demonstrates that the diminishing returns phenomenon applies to amino acid nutrition exactly as m,ould be predicted. The MPP line in Figure 7 corresponds to the expected MPP line in Figure 2 lysine should be fed until its cost is equal to the added value of the resultant body weight gain. Feeding beyond that point would be uneconomical. DIMINISHING RETURNS MODELS OF FEED FORM~JLATION Researchers have proposed two models of feed formulation that relate the protein and energy levels of feed to broiler feed intake and body weight gains [9, :LO]. The model of Miller et al. [ 101 was based on experiments conducted in the 1980s; that of Gonzalez-Alcorta et al. (the Gonzalez ModA) [9] (Table 2) on a Author Year Gain = f(pe) Donaldson ad. [7l Yoshida ad. [ll] Petersen [12] Petersen [13] Jackson [14] Petersen [15] Pesti ad. [16] a id Sell ad. [18] Gain = f(pe)

6 438 JAPR ECONOMICAL NUTRITION MODELLING Gj W 80 E.a YO Dietary Lysine FIGURE 5. The diminishing returns function of chick body weight to dietary lysine level [8] YO Dietary Lysine FIGURE 6. Dietary lysine utilization as a function of dietary lysine level [8]

7 Symposium PEST1 and MILLER E.r( - m,h 80 0 E.r( ep ba 40 ba W YO Dietary Lysine FIGURE 7. Dietary lysine marginal utilization as a function of dietary lysine level [8] mathematical analysis of various published data sets from around the world (Table 3). Although the Gonzalez Model contained sigdicant linear and quadratic terms for the response to dietary protein, the response to protein appears linear in the ranges depicted in Figures 8 and 9. The response to energy, however, was clearly nonlinear for body weight gain. This model is quite different from typical least-cost feed formulation models in that it includes terms for responses to nutrients and time or age. In determining maximum profit diets to feed, the model can choose higher protein and energy level diets that will result in target market weights sooner, or lower protein and/or energy level diets that wil result in slower achievement of the same market weights (Figure 8). Feed intakes that result from providing different protein and energy levels are determined in the calculation of maximum profit diets (body weight x valuehnit - feed intake x codunit). Note that Figure 9 shows feed intakes at only one age. These formulaticln models are actually supersets of typical feed formulation models currently used in industry: They can contain all the linear constraints that least-cost models presently contain. Nutrient minimums and maximums can be specified as in current models. Therefore, the worst-case scenario for application of these maximum profit feed TABLE 2. Model of Gonzalez-Alcorta 191 for the response of broiler chickens to dietarq protein and energy levels Body Weight Feed Intake Intercept Protein Level Protein Level 2 Energy Level Energy Level 2 Age

8 490 JAPR ECONOMICAL NUTRITION MODELLING TABLE 3. Comparison of coefficients of determination for models of feed intake as functions of protein and enerav ratios or levels from various published experiments 191 formulation models will be the same as the result of applying the least-cost model! Applying these models thus offers potential improved profits, essentially without risk. Estimates of the magnitude of savings achievable with the Gonzalez Model as opposed to typical minimums set by a commer- cial company were on the order of 0.50 to 0.75$/bird [9] during a period of relatively stable chicken, corn, and soybean meal prices in For a complex slaughtering 1,000,000 birds/wk, feed savings alone could exceed $3OO,OOO/yr. Similar savings may result from increasing efficiencies of scheduling for pro- 2.2 n 2.1 v 2 M rci ; 2.0 h a i Protein (g/kg) FIGURE 8. The body weight response of broiler chickens to dietary protein and energy levels; from the Gonzalez Model [9]

9 PEST1 and MILLER 4.05 Symposium 491 h 3.95 ii? W 1 0 E.z 2 c., 3.85 E u z G f # # # - =]ME = 3.2 :.ME = 3.4 = = ME = Protein (g/kg) FIGURE 9. The feed intake response of broiler chickens to dietary protein and energy levels; from the Gonzalez Model [9] cessing and precisely filling marketing orders when feed formulation models are an integral part of planning for the entire enterprise. ALTERNATE MODELS It is important to recognize that the Gonzalez Model is quite different from models that are not based on observations of the diminishing returns phenomenon in growing broilers. Other models have attempted to find the minimum amount of nutrients that will result in maximum performance of the animal. The model of Hurwitz et al. [19], for instance, is based on the premise that birds have a "requirement" for energy, protein, and amino acids for maintenance and growth. Protein and amino acid requirements are calculated from knowledge of the amount of tissue gain and the efficiency of nutrient utilization. This model assumes a constant utilization of amino acids from natural feedstuffs of 85%. Contrary to Figure 1, ii: assumes that growth is not a consequence of nutrient levels, but that nutrient "requirement:;" are a consequence of growth. The idea of a requirement based on some constant rate of utilization is in contrast to the observations of Baker [8] (Figures 5,6, and 7) and many others, that imino acids and protein follow diminishing re turns functions so that marginal utilization diminishes with increasing levels. An economic feeding level occurs where the value of the marginal physical product equals marginal input cost. The model of Hurwitz et al. [19], however, considers MPP is a constant 85% until maximum performance is reached, at which point it immediately falls to zero (without intermediate values). If this type of model is used to determine the "requirement" for some sub-optimal rate of growth, the difference in requirements would be based on the constant marginal utilization rate (85% for

10 492 JAPR ECONOMICAL NUTRITION MODELLING instance), not on the appropriate varying marginal utilization rate (Figure 7). GENETIC DIFFERENCES IN RESPONSE There is now clear evidence that there are differences in the response of different genetic stocks to dietary protein and amino acid concentrations [20, 21, 221. Leclercq's lines selected to be fat or lean have quite different feed intakes (Figure 10) although they grow at almost identical rates (Figure 11). They therefore utilize nutrients including energy, protein, and amino acids at quite different rates. We recently found very similar results in comparing so-called "fast growing" and "high yield" commercial lines of broilers [22]. The genetic differences in utilization suggest that the utilization rate needs to be determined for each genetic stock. Using models that base "requirements" on rates of growth and constant utilization rates will not accurately represent the biological processes involved nor reflect economic realities. 2.0 m W 2.m a 1.6 ; * P4 1.0 d APPLYING PRECISION- ORIENTED MODELS Utilizing models such as this article proposes [9, 101 will require considerable effort. Research in determining the response of various genetic stocks under each fm's conditions will be necessary. Since genetic stocks, housing conditions, and even season constantly change, constant attention to refining maximum profit models will be necessary, as will coordination among production managers, nutritionists, and processing and marketing managers. INCREASING PRECISION IN THE FUTURE Feed formulation should be at the center of each firm's production models for short-, medium-, and long-term planning. Our initial models have been designed to maximize profits relative only to live weight gain. But al factors related to live weight production that are important to producers may be added to profit maximization models if actual price dif- - lgonzalez Model - Lean Line II Fat Line Protein (g/kg) FIGURE 10. The body weight response of chickens selected for high levies of carcass fat or lean to dietary protein level [20], with a comparison to the Gonzalez Model 19)

11 Symposium PEST1 and MILLER 493 IGonzalez Model - Lean Line I -- Fat Line I 3.20 I Protein (g/kg) FIGURE 11. The feed intake response of chickensselected for high levlesof carcass fat or lean to dietary protein level [20], with a comparison to the Gonzalez Model [9] ferences can be attributed to these factors. Additional factors may include breast meat yield, percentage grade A carcasses, shelf life, carcass quality, and any other producer or consumer concerns. Consumer concerns could also include parameters such as skin pigmentation and acceptable carcass size distributions for each market. Once the models are developed they should be used in long-term planning for estimating the profitability of marketing goals and business expansion; in medium-term planning for feed ingredient purchasing; and in shortterm planning for feed delivery programs. Another short-term application will result when nutritionists coordinate the efforts of production and marketing segments of a company to precision-design birds for slaughter. Diet manipulation such as that shown in Figure 8 will be used by production managers to see that marketing managers have the best sizes of birds to sell. For instance, if marketing finds it has orders for relatively small carcasses in 2 wk but production observes that flocks due to be slaughtered then are well ahead of performance goals, a.ppropriate dietary manipulations can be applied to achieve maximum profits for the firm. Dynamic feed formulation modelswill not necessarily result in rnaximum technical feed efficiency for all broiler prices and feed costs. They should, however, result in maximum profitability, with optimum technical feed efficiency for a given set of prices and costs. The faster change occurs i n both the economic and technical aspects of production, the more valuable dynamic models will become. CONCLUSIONS AND APPLICATIONS 1. Present least-cost feed formulation models can find the combination of ingredients that meet nutrient specifications at least cost per unit of feed. However, {:hey cannot specify the protein and energy levels that result in maximum profits to the firm.

12 494 JAPR ECONOMICAL NUTRITION MODELLING 2. Birds responses to dietary energy, protein, and amino acids are diminishing returns phenomena, and should be evaluated economically as such. 3. Dynamic, maximum-profit feed formulation models can determine the protein and energy levels that result in the most economical use of feed ingredients. These models need to be incorporated into each firm s model for such diverse functions as enterprise planning, planning feed ingredient purchases, and scheduling feed delivery and slaughter. 4. Models based on the premise that growth rate determines requirements based on some fmed rate of nutrient utilization do not adequately represent the biological phenomena involved. 5. The adaptation of dynamic maximum profit feed formulation models will require considerable investments in research as well as coordination among managers in production, processing, and marketing. Our data suggest that such efforts will be worthwhile, especially in times when rapidly changing economic and/or technical conditions demand quick responses. 1. Bolden, S., Seaboard Farms Laboratories, 332 Tallassee Rd., Athens, GA Personal Communication. From a seminar presented at The University of Georgia. 2. Pesti, G.M. and B.R Miller, Animal Feed Formulation: Economic and Computer Applications. Van Nostrand Reinhold, New York, NY. 3. Almquist, H.J., Application of the law of diminishing returns to estimation of B-vitamins requirements for growth. Poultry Sci. 32:lOOl. 4. National Research Council, Nutrient Requirements of Poultry. 8th Edition. Natl. Acad. Press, Washington, DC. 5. National Research Council, Nutrient Requirements of Poultry. 9th Edition. Natl. Acad. Press, Washington, DC. 6. Fisher, C. and BJ. Wilson, Response to dietary energy concentration by growing chicks. Energy requirements of poult Pages in: Poultry Sci. Symposium #9, Br.7 oultry Sci. Ltd., Edinburgh, Scotland. 7. Donaldson, WE, G.F. Combs, and G.L Romoser, Studies on energy levels in poultry rations: The effect of calorie-protein ratio of the ration on growth, nutrient utilization, and body composition of chicks. Poultry Sci. 35:llOO. 8. Baker, D.H., Nutrient bioavailability in feedstuffs: me tho do lo^ for determining amino acid and B-vitamin availability in cercal grains and soybean meal. Pages 1-12 in: Proc. Georgia Nutr. Conf., Atlanta, GA. 9. Gonzalez-Alcorta, MJ., G.M. Pesti, and J.H. Dorfman, Maximizing profit in broiler production as prices change: A sim le approximation with practical value. Agribusiness 1OfS): Miller, B.R, RA. Arraes, and G.M. Pesti, Formulation of broiler finishing rations by quadratic programming. So. J. Agric. &on Yoshida, M., S. Hizikuro, H. Hoshii, and H. Morimoto, Effect of dietary protein and energy levels on the growth rate, feed efficiency, and carcass composition of chicks. Agric. Biol. Chem. 26( 10): Petersen, V.E, The protein-energy ratio in the diet and its influence on gain, feed conversion, and fat REFERENCES AND NOTES deposition in broiler chickens. Pages in: Fourteenth World s Poultry Sci. Cong., Madrid, Spain. 13. Petersen, V.E, The Influence of Energy Content and ProteiniEnergy Ratio of the Feed on Gain, Feed Conversion, and Slaughter Yield of Broilers. Report of the Natl. Inst. Anim. Sci., No Copenhagen, Denmark. 14. Jackson, S.E, The Effect of Dietary Energy on Performance, Body Composition, and Production Costs of Broiler Chickens. Unpublished M.S. Thesis, The University of Guelph, Guelph, ON, Canada. 15. Petersen, V.E, The Energy Content and the ProteinEnergy Ratio of Diets for Broilers and Its Influence on Body Weight Gain and Feed Conversion of Broiler Chickens. Report of The Natl. Inst. of him. Sci., No Copenhagen, Denmark. 16. Pesti, G.M., RA. Arraes, and B.R Miller, Use of the quadratic growth response to dietaxy protein and energy concentrations in least cost feed formulation. Poultry Sci. 65:104& Sell, J.L, R.J. Hasiak, and W.J. owings, Independent effects of dietary metabolizable energy and protein concentrations on erformance and carcass characteristics of tom turkeys. Foultry Sci. 64:1S Se4 J.L, P.R Ferket, C.R Angel, S.W. Scheideler, F. Escribano, and 1. Zafari, Performance and carcass characteristics of turkev toms as influenced bv dietary rotein and metabolizabie energy. Nutr. Rep. Inti. 40(5):9? Hunvitz, S., D. Sklan, and I. Bartov, New formal approaches to the determination of ener and amino acid requirements of chicks. Poultry Sci. Sy Leclercq, B. and G. Guy, Further investigations on rotein requirement of genetically lean or fat chickens.%r. Poultry Sci. 32: Leclercq, B., AM. Chagneau, T. Cochard, S. Hamzaoui, and M. Larbier, Comparative utilisation of sulphur-containing amino acids by genetically lean or fat chickens. Br. Poultry Sci Smlth, ER and G.M. Pesti, Influence of genotype and dietary rotein level on the performance of broilers. Poultry Sci.?5(1):87 (Abs).