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Impact of dietary amino acid and crude protein levels in broiler feeds on biological performance
©2009 Poultry Science Association, Inc.
Impact of dietary amino acid and crude protein levels in broiler feeds on biological performance G. M. Pesti1 Department of Poultry Science, The University of Georgia, Athens 30602-2772
SUMMARY The concept of a requirement for dietary protein has been controversial since it was discovered that proteins are composed of amino acids and that some amino acids are dietary essentials for maximum growth and performance. In addition to the 10 essential amino acids and 3 that can be accreted only from limited substrates, poultry need a quantity of amino acids to synthesize the other 8 that are needed to synthesize body proteins. Adding purified amino acids or amino acid precursors has been known for more than 50 yr to allow for reduced levels of intact proteins to provide adequate levels of essential and nonessential amino acids (CP). It has been recognized that individual essential amino acid requirements are functions of the total CP level. Increasing the total CP level while maintaining ideal ratios of essential amino acids increases growth, feed utilization efficiency, and carcass yields (i.e., decreases carcass fat). A published data set is used here to demonstrate 1) that potential problems arise from analyzing combined data sets inappropriately; 2) that in the overwhelming majority of studies, there is a positive response in growth (P < 0.0002) and feed utilization efficiency (P < 0.0002) to increasing dietary protein levels; 3) that the relationships are much stronger in faster growing broiler strain birds; and 4) that there is no clear break point or “requirement” for CP in the range of dietary protein levels typically studied. Regardless of whether it is called “CP level” or “essential + nonessential amino acid level,” there is no clear requirement, only a smooth response curve that approaches maxima at lower levels for growth, and then feed utilization efficiency, and then lean meat yield, and finally the minimum for carcass fat. As a result, decisions on feeding levels for essential and nonessential amino acids should depend on the input-output relationships and costs. Key words: broiler, amino acid, crude protein, requirement, model 2009 J. Appl. Poult. Res. 18:477–486 doi:10.3382/japr.2008-00105
DESCRIPTION OF PROBLEM The use of dietary CP level in feed formulation has been controversial since it was recognized that protein is merely the sum of amino acids in the feed ingredient, which may or may not be essential themselves. Before purified 1
Corresponding author: [email protected], [email protected]
methionine was available, a typical corn- and soybean meal-based broiler starter feed had to contain approximately 71% soybean meal and 14% corn to supply minimal levels of the essential amino acids. The feed had to contain 35.6% CP to supply all the essential amino acids at recommended levels [1]. When synthetic dl-meth-
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Primary Audience: Nutritionists, Researchers, Executives
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ferred to as the CP requirement. The 1994 NRC [1], for instance, set the CP requirement for 0- to 3-wk-old broilers at 23%. It was recognized that the amino acid requirements of the bird are proportional to the CP content of the diet [1, 2]. The ratios of amino acids in muscle and other tissues in the body of the bird are constant. Birds consuming lower protein levels synthesize smaller amounts of protein and so need less of each amino acid, and vice versa. Amino acids are needed in direct proportion to the dietary protein level [3–8]. One of the factors determining feed consumption in published studies [3–8] is the dietary protein level. With higher protein levels, some genetic strains maintain consumption levels but grow more, resulting in improved feed utilization efficiency, whereas other genetic strains consume less feed but maintain growth levels, resulting in improved feed utilization efficiency [9–13]. The concept that amino acids are required in proportion to one another to synthesize body proteins (or in proportion to the total essential
Table 1. The influence of synthetic amino acid level on the protein level of corn- and soybean meal-based diets1 Item Ingredient, % Corn, grain Soybean meal, 48% Poultry fat Limestone Defluorinated phosphorus Common salt Vitamin premix Mineral premix CuSO4 Coccidiostat dl-Methionine l-Threonine l-Lysine hydrochloride Composition (calculated), % ME, kcal/g Protein, % Calcium, % Total phosphorus, % Available phosphorus, % Valine, % Isoleucine, % Methionine, % Methionine + cysteine, % Threonine, % Lysine, % 1
UA = the amino acid was unavailable.
Unsupplemented
+Met
+Met +Lys
+Met +Lys +Thr
14.01 70.86 12.22 0.61 1.48 0.40 0.25 0.08 0.05 0.05 UA UA UA
57.21 33.91 5.46 0.64 1.73 0.40 0.25 0.08 0.05 0.05 0.23 UA UA
59.47 31.94 5.10 0.64 1.74 0.40 0.25 0.08 0.05 0.05 0.25 0.03 UA
62.42 29.29 4.62 0.64 1.76 0.40 0.25 0.08 0.05 0.05 0.27 0.07 0.09
3.20 35.60 0.90 0.74 0.45 1.63 1.54 0.50 1.04 1.37 2.13
3.20 21.61 0.90 0.68 0.45 0.98 0.88 0.55 0.90 0.80 1.15
3.20 20.89 0.90 0.68 0.45 0.95 0.85 0.56 0.90 0.80 1.10
3.20 20.00 0.90 0.67 0.45 0.90 0.80 0.58 0.90 0.80 1.10
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ionine became available, adding merely 0.23% dl-methionine to the feed allowed soybean meal to be decreased to approximately 34% and the protein level to 21.6% while still satisfying the essential amino acid requirements. Table 1 shows the composition of feeds formulated to meet essential amino acid but not CP requirements using the NRC [1] nutrient requirements and ingredient composition tables. Chickens fed low-protein feeds, despite having enough of each essential amino acid (to support excellent growth), failed to thrive and were excessively fat. It was realized that chickens require the essential amino acids plus some other amount of nonessential amino acids to synthesize protein at acceptable rates. Therefore, it was clear that chickens require not only the essential amino acids but also some other quantity of amino acids, which have been referred to as the “nonessential” amino acids. Clearly, some quantity of these nonessential amino acids is needed (essential) for growth. The sum of the essential and nonessential amino acids may also be re-
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• No obvious break point or requirement is defined by the model. No declaration of a protein requirement results in maximum technical performance. The goal is maximum economic efficiency, and nutrient levels must be chosen as a function of economics. • Each response value (y, gain, consumption, yield, etc.) is implicitly assumed to be different for each level of protein intake (x), unless the slope of the line is equal to zero. An inherent challenge with this approach is that results are dependent on choosing an appropriate model and in the error associated with the parameter estimates of the model. A second approach to determining appropriate CP levels in broiler diets is to supplement essential or nonessential amino acids while reducing CP levels and to test the hypothesis that the response to one combination of amino acids and CP level is different from another. This approach is fundamentally different from the approach in Figure 1 because 1) it is based on attempting to determine differences in response points, not fitting curves through them; and 2) the goal is to determine the minimum protein level that results in maximum performance. Maximum technical performance may or may not result in maximum economic efficiency. An inherent challenge with this approach is that small but very important differences in responses may not be declared as significant because of inadequate replication and inherent variation in the responses between individuals. Payne [15] assembled a data set from experiments conducted using the second approach, comparing responses from combinations of amino acid and CP levels. Payne [15] concluded, “It seems that the CP levels in broiler diets can be reduced by 3 to 4 percentage points without sacrificing performance provided that free amino acids are supplemented in the diet to equal the amino acid levels in a conventional diet.” Payne [15] presented bar graphs showing that within experiments, there were few detectable differences between lower CP diets with higher purified amino acid supplementation and higher CP with lower amino acid supplementation. The
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and nonessential amino acids) has been referred to as the “ideal amino acid balance” [14]. The concept of the ideal balance usually refers to ratios of amino acids to one another and often uses lysine levels as the anchor or reference. Amino acid requirements are determined in reference to lysine without regard for the need for nonessential amino acids or the total essential and nonessential amino acids (CP). Not only are growth rate and feed utilization efficiency dependent on dietary protein and energy levels, but the amount of carcass and, especially, abdominal fat are as well. The order of “requirements” (i.e., the maximum responses to CP levels) is as follows: 1) maximum live BW; 2) maximum feed utilization efficiency; 3) maximum carcass lean mass; and 4) minimum carcass fat. The changes in carcass yield (weight of salable product/live BW) caused by changing the dietary protein level may be on the order of 4%, which is enormous from an economic perspective [12, 13]. Ideally, amino acids would each be determined as a function of the total essential plus nonessential amino acids in the feed. The total of essential plus nonessential amino acids in the feed is usually estimated by determining the nitrogen content and by assuming that CP contains 16% nitrogen. The CP that maximizes profits can be chosen by maximizing the difference between the cost of feed consumption and yields of salable product minus any costs for waste disposal. Note that the cost of waste disposal may be negative if there is value in the wastes for fertilizer, fuel, and the like. The use of this approach was best illustrated in Ross technical bulletin 00/39 [13] (Figure 1). The important economic factors influenced by CP level are represented by nonlinear functions, which may be used to calculate profit-maximizing functions. Protein level, in this case, is actually a function of the digestible lysine level and all essential amino acid minima are kept in proportion to the digestible lysine level. The term, “percentage of Manual,” refers to the standard nutritional requirements or feeding levels that Ross Breeders [13] was recommending at the time. It is very important to recognize that when nonlinear models (as in Figure 1) are fitted to the data,
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was recognized that CP levels fed were dependent on age, and were therefore also a function of growth rate, the data set was divided into halves (faster and slower growing) and was reanalyzed.
MATERIALS AND METHODS The data set compiled by Payne [15] (Table 2) was entered into Microsoft Excel for graphing and was transferred to SAS [39] for statistical analysis. The statements used with SAS [39] were as follows:
Figure 1. The response of Ross 308 broilers to dietary protein at 42 d of age, indexed to performance on manual feeds (Ross recommendations). The fitted curves have the formula {y = k0 + k1 × [1 − exp(k3 × digestible lysine)]}. The response curve for eviscerated yield is linear. The axis is expressed as deviation of the dietary protein level from the recommended level. Abd. fat = abdominal fat; Evisc. yield = eviscerated yield.
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data set compiled by Payne [15] should be ideal to test the hypothesis that there is no response to CP level if adequate purified amino acids are supplemented (at least in the ranges studied), using the regression approach. The experiments included were all based on the hypothesis that CP levels could be decreased by supplementing synthetic amino acids. The objective of this research was to determine the influence of CP level on growth and FE by fitting simple linear models to the broiler data set compiled by Payne [15–38]. When it
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Pesti: AMINO ACIDS AND CRUDE PROTEIN Table 2. Data used in the analyses1 Exp. no.
Table 2 (Continued). Data used in the analyses1
CP, %
Gain, g/d
G:F, g of gain/g of feed
22.2 19.2 22.2 16.2 22.2 16.2 22.2 16.2 22.2 16.2 22.8 20.9 22.3 18.6 22.0 20.0 26.4 21.9 23.0 21.0 24.0 17.0 23.0 20.0 23.0 17.0 23.0 17.0 23.0 21.0 23.0 20.3 23.0 20.1 23.0 19.7 23.0 17.8 23.0 17.4 23.0 16.5 23.2 18.6 24.0 18.5 23.4 20.6 23.0 19.0 23.0 19.0 23.0 19.0 23.0
29.97 28.04 29.27 28.32 28.70 28.50 26.50 25.91 28.98 29.60 33.86 34.50 41.50 40.76 37.60 36.20 37.70 36.50 28.60 26.50 33.30 29.60 36.50 33.80 36.50 31.80 37.00 35.10 32.30 32.30 25.30 27.80 28.90 31.30 28.90 31.00 36.70 38.00 33.00 34.60 33.90 36.60 46.70 44.30 52.20 46.90 43.90 42.60 20.70 20.80 20.70 20.60 20.50 21.10 19.70
0.817 0.759 0.797 0.807 0.766 0.801 0.808 0.791 0.800 0.797 0.873 0.876 0.764 0.756 0.709 0.694 0.758 0.714 0.694 0.640 0.691 0.613 0.712 0.680 0.712 0.630 0.703 0.690 0.630 0.617 0.559 0.595 0.541 0.585 0.541 0.571 0.654 0.617 0.654 0.617 0.637 0.625 0.739 0.679 0.762 0.710 0.753 0.723 0.675 0.660 0.675 0.672 0.671 0.687 0.682 Continued
Exp. no. 312 322 322 332 332 342 342 35 35 36 36 37 37 38 38 39 39 40 40 41 41 42 42 43 43 45 45 46 46 47 47 48 48 49 49 50 50 51 51 52 52 53 53 54 54 55 55 3B2 3B2 1
CP, %
Gain, g/d
G:F, g of gain/g of feed
19.0 23.0 19.0 23.0 19.0 23.0 19.0 23.0 19.0 20.9 17.1 18.3 15.9 19.0 16.6 19.0 16.6 19.4 16.4 19.4 16.4 22.0 19.0 22.0 16.0 22.0 19.0 22.0 16.0 17.6 13.5 20.6 18.2 21.5 16.5 19.0 17.0 19.4 18.2 19.4 16.7 17.2 15.9 17.2 14.7 15.6 11.7 22.2 16.2
19.90 19.30 19.40 19.10 18.90 19.10 19.30 45.40 44.90 41.18 37.49 42.30 38.90 50.10 47.60 50.10 47.00 44.00 43.90 44.00 44.70 61.00 60.60 61.00 59.80 62.00 60.60 62.00 57.00 73.73 68.09 81.00 78.80 90.60 86.40 75.10 73.60 81.60 80.60 81.60 80.20 79.00 76.00 79.00 73.30 69.69 64.90 28.70 27.79
0.680 0.675 0.696 0.675 0.661 0.697 0.694 0.776 0.771 0.790 0.690 0.487 0.463 0.494 0.469 0.494 0.474 0.458 0.437 0.458 0.466 0.487 0.478 0.487 0.466 0.538 0.511 0.538 0.488 0.560 0.520 0.490 0.500 0.479 0.427 0.433 0.431 0.478 0.478 0.478 0.470 0.379 0.372 0.379 0.366 0.420 0.440 0.766 0.806
From Payne [15]. The half of all data sets used showing the least growth.
2
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12 12 22 22 32 32 42 42 52 52 6 62 7 7 82 82 9 9 122 122 142 142 152 152 162 162 172 172 182 182 192 192 202 202 212 212 22 22 232 232 242 242 25 25 26 26 27 27 282 282 292 292 302 302 312
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Table 3. Comparison of ANOVA results for gain and feed utilization efficiency (g of gain/g of feed) from different models Source of variation
df
SE of estimate
Pr > |t|
92.7689 −2.51556
12.5099 0.62610
<0.0001 0.0001
30.0526 0.2918
2.0625 0.0725
<0.0001 <0.0001 <0.0001
0.2029 0.0211
0.0816 0.0041
0.0145 <0.0001
0.6371 0.0041
0.0287 0.0010
<0.0001 0.0002 0.0037
R2 0.137
0.997
0.208
0.987
1
Pr = probability.
PROC GLM; model BWG FE = CP, and PROC GLM; class EXPT; BWG FE = CP EXPT, where BWG is daily BW gain (g/d), FE is feed efficiency (g of gain/g of consumption), CP is dietary CP level (%), and EXPT is experiment.
RESULTS If the gain data are analyzed as a simple collection of data points from the literature without regard for the individual experiments from which they came, CP is a very highly significant contributor to the variation in BW gain (Table 3 and Figure 2), and CP has a negative effect on BW gain (it is toxic). If each experiment from which the data came is also included in the analysis, CP is again a significant contributor to the variation in BW gain, but the coefficient is positive (Table 3 and Figure 3). Each unit (percentage) of protein increased daily BW gain (g) by 0.2918 ± 0.0724. A total of 71.2% of the data sets had positive slopes for BW gain as a function of dietary CP level. If the FE data are analyzed as a simple collection of data from the literature without regard
for the individual experiments from which they came, CP is a very highly significant contributor to the variation in FE (Table 3 and Figure 4), and CP has a positive effect on FE (G:F). If each experiment from which the data came is also included in the analysis, CP is again a significant contributor to the variation in FE, and the coefficient is again positive (Table 3). Each unit (percentage) of protein increased FE by 0.0041 ± 0.0010. A total of 75.0% of the data sets had positive slopes for FE as a function of dietary CP level.
Figure 2. The relationship between ADG and dietary protein level (PL). Holistic analysis of data from 52 experiments. Model: ADG = f(PL).
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ADG as a function of CP level (CP, %) Intercept 1 CP 1 Error 102 ADG as a function of CP level (CP, %) and experiment Intercept 1 CP 1 Experiment 51 Error 52 Feed utilization as a function of CP level (CP, %) 1 Intercept 1 CP 102 Error Feed utilization as a function of CP level (CP, %) and experiment 1 Intercept 1 CP 51 Experiment Error 52
Parameter estimate
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These results make it clear that CP level is still a significant contributor to variation in both broiler growth and FE, even when purified amino acids are added to the lower CP feeds (from the collection of data in Table 2). The BW responses in Figure 3 are still increasing, similar to the BW responses in Figure 1 (between 100 and 110% of manual recommendations). Similarly, the FE responses in Figure 4 are increasing, similar to the FE responses in Figure 1 (between 90 and 100% of manual recommendations). The overall conclusion from the data set compiled by Payne [15] should be that both amino acid supplementation and CP levels are important in determining growth responses of broilers (at least in the ranges studied). The conclusions of Payne [15] are quite correct from the perspective of exam-
Figure 4. The relationship between FE and dietary protein level (PL). Holistic analysis of data from 26 experiments with the highest daily gains. Model: FE = f(PL).
Figure 3. The relationship between ADG and dietary protein level (PL). Holistic analysis of 52 experiments (EXP). Model: ADG = f(PL, EXP).
When only the data from the 26 research trials with birds with the lowest BW gains were considered, no significant effects of protein level on BW gain (P < 0.2830) or FE (P < 0.1693) were observed. However, when only the data from the 26 research trials with birds with the highest BW gains were considered, highly significant effects of protein level on BW gain (P < 0.0001) and FE (P < 0.0001) were observed (the independent variable “experiment” was included in the models). Each unit (percentage) of protein increased daily BW gain (g) by 0.6061 ± 0.1063 and FE by 0.0072 ± 0.0120. A total of 82.8% of the data sets had positive slopes for BW gain as a function of dietary CP level.
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DISCUSSION
ining whether 2 points in each experiment can be declared as significantly different at P < 0.05. The problem is that each experiment should come with a disclaimer stating that “because of variability in the data, differences smaller than some percentages could not reliably be detected.” Finding no significant differences should not be taken to mean that no differences existed. By pooling the data as in Table 3, it becomes clear that CP level really is having some significant effect overall (P < 0.0001 for gain, and P = 0.0002 for feed utilization efficiency). Whether that effect is important is an economic question: Is the cost of additional protein offset by the increased BW, breast meat yield, and so forth? That is not to imply that all the experiments listed in Table 2 would have shown significant responses to BW and feed utilization efficiency had there been adequate replication. Body weight gain and FE slopes, for instance, approach zero in the interval from 110 to 120% of manual CP recommendations in Figure 1. Had the experiments been conducted in this range, certainly it would have been extremely difficult to declare any differences as significant with the resources most researchers have to provide replication. Breast meat and eviscerated yield for both sexes and abdominal fat for females, however, still showed linear changes in the manual CP recommendations at 110 to 120% and need to be considered even though BW and FE are not changing in any detectable amounts. Whether significant differences can be detected depends on several factors, including 1)
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dom from 102 to 51. However, 51 df is still adequate to show that ADG and CP are related (less than 2 chances in 10,000 that observed effects are due to chance). The R2 values, the amount of variation described by the experimental model, increases from 0.137 to 0.997 when the effect of experiment is accounted for. Clearly, most of the variation in the ADG data in this data set is due to experimental variables other than dietary CP level. When differences in experiment are accounted for in the statistical model, ADG appears to be directly proportional to percentage of CP (positive coefficient for percentage of CP; Table 3 and Figure 2) in the ranges studied. The slower growing birds may not have shown responses to CP for several reasons: 1) they may simply have been younger and so may have responded differently physiologically; 2) their environmental (growing) conditions may have been such that they were not near their genetic potential; or 3) they may have been of specific genetic stocks that showed little growth response to dietary CP level in the ranges being studied. The NRC [1] emphasized the increasing importance of developing comprehensive models: Generally, as dietary protein level increases, essential amino acid requirements (expressed as a percentage of the diet) increase, although when expressed as a percentage of the protein, essential amino acid requirements are little affected. . . . These observations demonstrate the importance of maintaining a balance among the concentrations of essential and nonessential amino acids in poultry diets. Optimal balance is important for efficient utilization of dietary protein. The protein and amino acid concentrations presented as requirements herein are intended to support maximum growth and production. Achieving maximum growth and production, however, may not always ensure maximum economic returns, particularly when prices of protein sources are high. If decreased performance can be tolerated, dietary concentrations of amino acids may, accordingly, be reduced somewhat to maximize economic returns.
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the growth rate of the birds, 2) the quality (digestibility) of the ingredients, 3) the magnitude of the CP reduction, 4) the amount of experimental variation, and 5) the number of replicates per treatment. The more imbalanced a feed is to begin with, because of the individual ingredients and their qualities, the greater will be the detectable differences in protein level. When more is known about ingredient quality, such as individual amino acid digestibilities, then better amino balances can be achieved and more of the essential amino acids will be incorporated into body protein and less will be oxidized and metabolized. The approach taken in the experiments whose results are summarized in Table 3 and Figures 2 to 4 does not directly address the questions of 1) what the ratio of essential to nonessential amino acids should be, or 2) what the response is to total essential and nonessential amino acids (CP). Collectively, the results suggest little response to dietary protein level in the younger and slower growing birds. This is consistent with recommendations of relatively high protein levels when birds are young and growing at slow (absolute g/d) rates. However, when birds are older and growing at faster rates, the protein levels fed were limiting growth and feed utilization efficiency in the majority of cases, resulting in very high probabilities that the observed differences were not due to chance. In experiments showing the responses to protein level (despite the lower protein diets being better balanced), the real consideration should be, “Is the cost of the additional protein at least offset by the additional returns from increased growth rate or less feed per unit of salable product?” These analyses illustrate several potential problems that may occur when analyzing data sets made from a collection of results from experiments with many design differences. The initial analysis simply relating all ADG = f (CP) (Table 3 and Figure 2) suggests that CP is toxic in the range studied (note the negative coefficient for CP in Table 3). This apparent relationship may simply be due to the different experimental conditions used: younger chicks tend to be fed higher CP levels but naturally have lower ADG. Including “experiment” in the regression model (Table 3) lowers error degrees of free-
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Pesti: AMINO ACIDS AND CRUDE PROTEIN
CONCLUSIONS AND APPLICATIONS
1. The choice of the appropriate statistical model is critical to making appropriate conclusions about the relationship between dietary protein level, amino acid supplementation, and broiler performance. 2. Although individual experiments may seem to show no “significant” response to dietary protein level (even with amino acid supplementation), when the data are pooled with an appropriate regression model, clear responses to dietary protein are obvious and are highly significant. 3. Essential amino acid balance and total amino acid levels (CP or essential plus nonessential amino acids) should be considered to optimize growth and to maximize profits. Simply lowering CP levels by supplementing amino acids may not result in maximum performance or profits.
REFERENCES AND NOTES 1. NRC. 1994. Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 2. Almquist, H. J. 1947. Evaluation of amino acid requirements by observations on the chick. J. Nutr. 34:543– 563.
3. Almquist, H. J. 1952. Amino acid requirements of chickens and turkeys—A review. Poult. Sci. 31:966 –981. 4. Boomgaardt, J., and D. H. Baker. 1971. Tryptophan requirement of growing chicks as affected by dietary protein level. J. Anim. Sci. 33:595–599. 5. Boomgaardt, J., and D. H. Baker. 1973. The lysine requirement of growing chicks fed sesame meal-gelatin diets at three protein levels. Poult. Sci. 52:586–591. 6. Morris, T. R., K. Al-Azzawi, R. M. Gous, and G. L. Simpson. 1987. Effects of protein concentration on responses to dietary lysine by chicks. Br. Poult. Sci. 28:185–195. 7. Mendonca, C., and L. S. Jensen. 1989. Influence of protein concentration on the sulfur-containing amino acid requirement of broiler chickens. Br. Poult. Sci. 30:889– 898. 8. Leclercq, B. 1983. The influence of dietary protein content on the performance of genetically lean or fat growing chickens. Br. Poult. Sci. 24:581–587. 9. Leclercq, B., and G. Guy. 1991. Further investigations on protein requirement of genetically lean and fat chickens. Br. Poult. Sci. 32:789–798. 10. Alleman, F., J. Michel, A. M. Chagneau, and B. Leclercq. 2000. The effects of dietary protein independent of essential amino acids on growth and body composition in genetically lean and fat chickens. Br. Poult. Sci. 41:214–218. 11. Smith, E. R., G. M. Pesti, R. I. Bakalli, G. O. Ware, and J. F. M. Menten. 1998. Further studies on the influence of genotype and dietary protein on the performance of broilers. Poult. Sci. 77:1678–1687. 12. Smith, E. R., and G. M. Pesti. 1998. Influence of broiler strain cross and dietary protein on the performance of broilers. Poult. Sci. 77:276–281. 13. Aviagen. 2000. Broilers, Protein and Profit. Ross Tech. 00/39. Aviagen, Newbridge, Midlothian, Scotland, UK. 14. Emmert, J. L., and D. H. Baker. 1997. Use of the ideal protein concept for precision formulation of amino acid levels in broiler diets. J. Appl. Poult. Res. 6:462–470. 15. Payne, R. L. 2007. The potential for using low crude protein diets for broilers and turkeys. Degussa AminoNews 8:2–13. 16. Aletor, V. A., I. I. Hamid, and E. Pfeffer. 2000. Low protein amino acid-supplemented diets in broiler chickens: Effects on performance, carcass characteristics, whole-body composition and efficiencies of nutrient utilization. J. Sci. Food Agric. 80:547–554. 17. Bregendahl, K., J. S. Sell, and D. R. Zimmerman. 2002. Effect of low protein diets on growth performance and body composition of broiler chicks. Poult. Sci. 81:1156– 1167. 18. Brooks, S. E., H. M. Allen, and J. D. Firman. 2003. Utilization of low crude protein diets fed to 0–3 wk broilers. Poult. Sci. 82(Suppl. 1):37. (Abstr.) 19. Cabel, M. C., and P. W. Waldroup. 1991. Effect of dietary protein level and length of feeding on performance and abdominal fat pad content of broiler chickens. Poult. Sci. 70:1550–1558. 20. Corzo, A., M. T. Kidd, D. J. Burnham, and B. J. Kerr. 2004. Dietary glycine needs of broiler chicks. Poult. Sci. 83:1382–1384. 21. Fancher, B. I., and L. S. Jensen. 1989. Dietary protein level and essential amino acid content: Influence upon female broiler performance during the grower period. Poult. Sci. 68:897–908.
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Clearly, it is becoming more important not to waste dietary CP from both cost and environmental waste perspectives. Amino acid supplementation is one key factor in reducing CP levels in practical broiler feeds (Table 1). Optimizing, and not minimizing, CP levels is another. The idea of comparing low CP plus nonessential amino acids with some higher standard implies that the goal of feed formulation is merely to achieve some standard performance. However, it is just as clear that feed formulation should have as its goal achieving a compromise between diet cost and performance. Performance increasingly means optimizing eviscerated and breast meat yields, not just maximizing BW and FE. The emphasis of amino acid and protein research should be on developing equations that can be used to relate inputs (costs) and outputs (performance) to maximize profits under various environmental conditions with each genetic stock.
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1999. Ideal amino acid profile and dietary lysine specification for broiler chickens of 20 to 40 days of age. Br. Poult. Sci. 40:257–265. 31. Parr, J. F., and J. D. Summers. 1991. The effect of minimizing amino acid excesses in broiler diets. Poult. Sci. 70:1540–1549. 32. Pesti, G. M., and C. F. Smith. 1984. The response of growing broiler chickens to dietary protein, energy and added fat contents. Br. Poult. Sci. 25:127–138. 33. Pinchasov, Y., C. X. Mendonca, and L. S. Jensen. 1990. Broiler chick response to low protein diets supplemented with synthetic amino acids. Poult. Sci. 69:1950– 1955. 34. Robbins, K. R. 1987. Threonine requirement of the broiler chick as affected by protein level and source. Poult. Sci. 66:1531–1534. 35. Schutte, J. B., W. Smink, and M. Pack. 1997. Requirement of young broiler chicks for glycine + serine. Arch. Geflugelkd. 61:43–47. 36. Si, J., C. A. Fritts, P. W. Waldroup, and D. J. Burnham. 2004. Effects of tryptophan to large neutral amino acid ratios and overall amino acid levels on utilization of diets low in crude protein by broilers. J. Appl. Poult. Res. 13:570–578. 37. Si, J., C. A. Fritts, P. W. Waldroup, and D. J. Burnham. 2004. Effects of excess methionine from meeting needs for sulfur amino acids on utilization of diets low in crude protein by broiler chicks. J. Appl. Poult. Res. 13:579–587. 38. Waldroup, P. W. 2000. Feeding programs for broilers: The challenge of low protein diets. Pages 119–134 in Proc. 47th Annu. Maryland Nutr. Conf. Maryland Feed Ind. Counc. Inc., College Park, MD. 39. SAS Institute. 2001. SAS User’s Guide: Statistics. Version 8.02 Edition. SAS Inst. Inc., Cary, NC.
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22. Fancher, B. I., and L. S. Jensen. 1989. Male broiler performance during the starting and growing periods as affected by dietary protein, essential amino acids, and potassium levels. Poult. Sci. 68:1385–1395. 23. Ferguson, N. S., R. S. Gates, J. L. Taraba, A. H. Cantor, A. J. Pescatore, M. L. Straw, M. J. Ford, and D. J. Burnham. 1998. The effect of dietary protein and phosphorus on ammonia concentration and litter composition in broilers. Poult. Sci. 77:1085–1093. 24. Ferguson, N. S., R. S. Gates, J. L. Taraba, A. H. Cantor, A. J. Pescatore, M. L. Straw, M. J. Ford, and D. J. Burnham. 1998. The effect of dietary crude protein on growth, ammonia concentration and litter composition in broilers. Poult. Sci. 77:1481–1487. 25. Fritts, C. A., A. Corzo, and M. T. Kidd. 2004. Chick responses to diets differing in essential and nonessential amino acids. Poult. Sci. 83(Suppl. 1):443. (Abstr.) 26. Han, Y., H. Suzuki, C. M. Parsons, and D. H. Baker. 1992. Amino acid fortification of a low protein corn and soybean meal diet for chicks. Poult. Sci. 71:1168–1178. 27. Heger, J., and M. Pack. 1996. Effects of dietary glycine + serine on starting broiler chick performance as influenced by dietary crude protein levels. Agribiol. Res. 49:257–265. 28. Kerr, B. J., and M. T. Kidd. 1999. Amino acid supplementation of low-protein broiler diets: 1. Glutamic acid and indispensable amino acid supplementation. J. Appl. Poult. Res. 8:298–309. 29. Kerr, B. J., and M. T. Kidd. 1999. Amino acid supplementation of low-protein broiler diets: 2. Formulation on an ideal amino acid basis. J. Appl. Poult. Res. 8:310–320. 30. Mack, S., D. Bercovici, G. de Groote, B. Leclercq, M. Lippens, M. Pack, J. B. Schutte, and S. vanCauwenberghe.
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Impact of dietary amino acid and crude protein levels in broiler feeds on biological performance G. M. Pesti1 Department of Poultry Science, The University of Georgia, Athens 30602-2772
SUMMARY The concept of a requirement for dietary protein has been controversial since it was discovered that proteins are composed of amino acids and that some amino acids are dietary essentials for maximum growth and performance. In addition to the 10 essential amino acids and 3 that can be accreted only from limited substrates, poultry need a quantity of amino acids to synthesize the other 8 that are needed to synthesize body proteins. Adding purified amino acids or amino acid precursors has been known for more than 50 yr to allow for reduced levels of intact proteins to provide adequate levels of essential and nonessential amino acids (CP). It has been recognized that individual essential amino acid requirements are functions of the total CP level. Increasing the total CP level while maintaining ideal ratios of essential amino acids increases growth, feed utilization efficiency, and carcass yields (i.e., decreases carcass fat). A published data set is used here to demonstrate 1) that potential problems arise from analyzing combined data sets inappropriately; 2) that in the overwhelming majority of studies, there is a positive response in growth (P < 0.0002) and feed utilization efficiency (P < 0.0002) to increasing dietary protein levels; 3) that the relationships are much stronger in faster growing broiler strain birds; and 4) that there is no clear break point or “requirement” for CP in the range of dietary protein levels typically studied. Regardless of whether it is called “CP level” or “essential + nonessential amino acid level,” there is no clear requirement, only a smooth response curve that approaches maxima at lower levels for growth, and then feed utilization efficiency, and then lean meat yield, and finally the minimum for carcass fat. As a result, decisions on feeding levels for essential and nonessential amino acids should depend on the input-output relationships and costs. Key words: broiler, amino acid, crude protein, requirement, model 2009 J. Appl. Poult. Res. 18:477–486 doi:10.3382/japr.2008-00105
DESCRIPTION OF PROBLEM The use of dietary CP level in feed formulation has been controversial since it was recognized that protein is merely the sum of amino acids in the feed ingredient, which may or may not be essential themselves. Before purified 1
Corresponding author: [email protected], [email protected]
methionine was available, a typical corn- and soybean meal-based broiler starter feed had to contain approximately 71% soybean meal and 14% corn to supply minimal levels of the essential amino acids. The feed had to contain 35.6% CP to supply all the essential amino acids at recommended levels [1]. When synthetic dl-meth-
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Primary Audience: Nutritionists, Researchers, Executives
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ferred to as the CP requirement. The 1994 NRC [1], for instance, set the CP requirement for 0- to 3-wk-old broilers at 23%. It was recognized that the amino acid requirements of the bird are proportional to the CP content of the diet [1, 2]. The ratios of amino acids in muscle and other tissues in the body of the bird are constant. Birds consuming lower protein levels synthesize smaller amounts of protein and so need less of each amino acid, and vice versa. Amino acids are needed in direct proportion to the dietary protein level [3–8]. One of the factors determining feed consumption in published studies [3–8] is the dietary protein level. With higher protein levels, some genetic strains maintain consumption levels but grow more, resulting in improved feed utilization efficiency, whereas other genetic strains consume less feed but maintain growth levels, resulting in improved feed utilization efficiency [9–13]. The concept that amino acids are required in proportion to one another to synthesize body proteins (or in proportion to the total essential
Table 1. The influence of synthetic amino acid level on the protein level of corn- and soybean meal-based diets1 Item Ingredient, % Corn, grain Soybean meal, 48% Poultry fat Limestone Defluorinated phosphorus Common salt Vitamin premix Mineral premix CuSO4 Coccidiostat dl-Methionine l-Threonine l-Lysine hydrochloride Composition (calculated), % ME, kcal/g Protein, % Calcium, % Total phosphorus, % Available phosphorus, % Valine, % Isoleucine, % Methionine, % Methionine + cysteine, % Threonine, % Lysine, % 1
UA = the amino acid was unavailable.
Unsupplemented
+Met
+Met +Lys
+Met +Lys +Thr
14.01 70.86 12.22 0.61 1.48 0.40 0.25 0.08 0.05 0.05 UA UA UA
57.21 33.91 5.46 0.64 1.73 0.40 0.25 0.08 0.05 0.05 0.23 UA UA
59.47 31.94 5.10 0.64 1.74 0.40 0.25 0.08 0.05 0.05 0.25 0.03 UA
62.42 29.29 4.62 0.64 1.76 0.40 0.25 0.08 0.05 0.05 0.27 0.07 0.09
3.20 35.60 0.90 0.74 0.45 1.63 1.54 0.50 1.04 1.37 2.13
3.20 21.61 0.90 0.68 0.45 0.98 0.88 0.55 0.90 0.80 1.15
3.20 20.89 0.90 0.68 0.45 0.95 0.85 0.56 0.90 0.80 1.10
3.20 20.00 0.90 0.67 0.45 0.90 0.80 0.58 0.90 0.80 1.10
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ionine became available, adding merely 0.23% dl-methionine to the feed allowed soybean meal to be decreased to approximately 34% and the protein level to 21.6% while still satisfying the essential amino acid requirements. Table 1 shows the composition of feeds formulated to meet essential amino acid but not CP requirements using the NRC [1] nutrient requirements and ingredient composition tables. Chickens fed low-protein feeds, despite having enough of each essential amino acid (to support excellent growth), failed to thrive and were excessively fat. It was realized that chickens require the essential amino acids plus some other amount of nonessential amino acids to synthesize protein at acceptable rates. Therefore, it was clear that chickens require not only the essential amino acids but also some other quantity of amino acids, which have been referred to as the “nonessential” amino acids. Clearly, some quantity of these nonessential amino acids is needed (essential) for growth. The sum of the essential and nonessential amino acids may also be re-
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• No obvious break point or requirement is defined by the model. No declaration of a protein requirement results in maximum technical performance. The goal is maximum economic efficiency, and nutrient levels must be chosen as a function of economics. • Each response value (y, gain, consumption, yield, etc.) is implicitly assumed to be different for each level of protein intake (x), unless the slope of the line is equal to zero. An inherent challenge with this approach is that results are dependent on choosing an appropriate model and in the error associated with the parameter estimates of the model. A second approach to determining appropriate CP levels in broiler diets is to supplement essential or nonessential amino acids while reducing CP levels and to test the hypothesis that the response to one combination of amino acids and CP level is different from another. This approach is fundamentally different from the approach in Figure 1 because 1) it is based on attempting to determine differences in response points, not fitting curves through them; and 2) the goal is to determine the minimum protein level that results in maximum performance. Maximum technical performance may or may not result in maximum economic efficiency. An inherent challenge with this approach is that small but very important differences in responses may not be declared as significant because of inadequate replication and inherent variation in the responses between individuals. Payne [15] assembled a data set from experiments conducted using the second approach, comparing responses from combinations of amino acid and CP levels. Payne [15] concluded, “It seems that the CP levels in broiler diets can be reduced by 3 to 4 percentage points without sacrificing performance provided that free amino acids are supplemented in the diet to equal the amino acid levels in a conventional diet.” Payne [15] presented bar graphs showing that within experiments, there were few detectable differences between lower CP diets with higher purified amino acid supplementation and higher CP with lower amino acid supplementation. The
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and nonessential amino acids) has been referred to as the “ideal amino acid balance” [14]. The concept of the ideal balance usually refers to ratios of amino acids to one another and often uses lysine levels as the anchor or reference. Amino acid requirements are determined in reference to lysine without regard for the need for nonessential amino acids or the total essential and nonessential amino acids (CP). Not only are growth rate and feed utilization efficiency dependent on dietary protein and energy levels, but the amount of carcass and, especially, abdominal fat are as well. The order of “requirements” (i.e., the maximum responses to CP levels) is as follows: 1) maximum live BW; 2) maximum feed utilization efficiency; 3) maximum carcass lean mass; and 4) minimum carcass fat. The changes in carcass yield (weight of salable product/live BW) caused by changing the dietary protein level may be on the order of 4%, which is enormous from an economic perspective [12, 13]. Ideally, amino acids would each be determined as a function of the total essential plus nonessential amino acids in the feed. The total of essential plus nonessential amino acids in the feed is usually estimated by determining the nitrogen content and by assuming that CP contains 16% nitrogen. The CP that maximizes profits can be chosen by maximizing the difference between the cost of feed consumption and yields of salable product minus any costs for waste disposal. Note that the cost of waste disposal may be negative if there is value in the wastes for fertilizer, fuel, and the like. The use of this approach was best illustrated in Ross technical bulletin 00/39 [13] (Figure 1). The important economic factors influenced by CP level are represented by nonlinear functions, which may be used to calculate profit-maximizing functions. Protein level, in this case, is actually a function of the digestible lysine level and all essential amino acid minima are kept in proportion to the digestible lysine level. The term, “percentage of Manual,” refers to the standard nutritional requirements or feeding levels that Ross Breeders [13] was recommending at the time. It is very important to recognize that when nonlinear models (as in Figure 1) are fitted to the data,
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was recognized that CP levels fed were dependent on age, and were therefore also a function of growth rate, the data set was divided into halves (faster and slower growing) and was reanalyzed.
MATERIALS AND METHODS The data set compiled by Payne [15] (Table 2) was entered into Microsoft Excel for graphing and was transferred to SAS [39] for statistical analysis. The statements used with SAS [39] were as follows:
Figure 1. The response of Ross 308 broilers to dietary protein at 42 d of age, indexed to performance on manual feeds (Ross recommendations). The fitted curves have the formula {y = k0 + k1 × [1 − exp(k3 × digestible lysine)]}. The response curve for eviscerated yield is linear. The axis is expressed as deviation of the dietary protein level from the recommended level. Abd. fat = abdominal fat; Evisc. yield = eviscerated yield.
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data set compiled by Payne [15] should be ideal to test the hypothesis that there is no response to CP level if adequate purified amino acids are supplemented (at least in the ranges studied), using the regression approach. The experiments included were all based on the hypothesis that CP levels could be decreased by supplementing synthetic amino acids. The objective of this research was to determine the influence of CP level on growth and FE by fitting simple linear models to the broiler data set compiled by Payne [15–38]. When it
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Pesti: AMINO ACIDS AND CRUDE PROTEIN Table 2. Data used in the analyses1 Exp. no.
Table 2 (Continued). Data used in the analyses1
CP, %
Gain, g/d
G:F, g of gain/g of feed
22.2 19.2 22.2 16.2 22.2 16.2 22.2 16.2 22.2 16.2 22.8 20.9 22.3 18.6 22.0 20.0 26.4 21.9 23.0 21.0 24.0 17.0 23.0 20.0 23.0 17.0 23.0 17.0 23.0 21.0 23.0 20.3 23.0 20.1 23.0 19.7 23.0 17.8 23.0 17.4 23.0 16.5 23.2 18.6 24.0 18.5 23.4 20.6 23.0 19.0 23.0 19.0 23.0 19.0 23.0
29.97 28.04 29.27 28.32 28.70 28.50 26.50 25.91 28.98 29.60 33.86 34.50 41.50 40.76 37.60 36.20 37.70 36.50 28.60 26.50 33.30 29.60 36.50 33.80 36.50 31.80 37.00 35.10 32.30 32.30 25.30 27.80 28.90 31.30 28.90 31.00 36.70 38.00 33.00 34.60 33.90 36.60 46.70 44.30 52.20 46.90 43.90 42.60 20.70 20.80 20.70 20.60 20.50 21.10 19.70
0.817 0.759 0.797 0.807 0.766 0.801 0.808 0.791 0.800 0.797 0.873 0.876 0.764 0.756 0.709 0.694 0.758 0.714 0.694 0.640 0.691 0.613 0.712 0.680 0.712 0.630 0.703 0.690 0.630 0.617 0.559 0.595 0.541 0.585 0.541 0.571 0.654 0.617 0.654 0.617 0.637 0.625 0.739 0.679 0.762 0.710 0.753 0.723 0.675 0.660 0.675 0.672 0.671 0.687 0.682 Continued
Exp. no. 312 322 322 332 332 342 342 35 35 36 36 37 37 38 38 39 39 40 40 41 41 42 42 43 43 45 45 46 46 47 47 48 48 49 49 50 50 51 51 52 52 53 53 54 54 55 55 3B2 3B2 1
CP, %
Gain, g/d
G:F, g of gain/g of feed
19.0 23.0 19.0 23.0 19.0 23.0 19.0 23.0 19.0 20.9 17.1 18.3 15.9 19.0 16.6 19.0 16.6 19.4 16.4 19.4 16.4 22.0 19.0 22.0 16.0 22.0 19.0 22.0 16.0 17.6 13.5 20.6 18.2 21.5 16.5 19.0 17.0 19.4 18.2 19.4 16.7 17.2 15.9 17.2 14.7 15.6 11.7 22.2 16.2
19.90 19.30 19.40 19.10 18.90 19.10 19.30 45.40 44.90 41.18 37.49 42.30 38.90 50.10 47.60 50.10 47.00 44.00 43.90 44.00 44.70 61.00 60.60 61.00 59.80 62.00 60.60 62.00 57.00 73.73 68.09 81.00 78.80 90.60 86.40 75.10 73.60 81.60 80.60 81.60 80.20 79.00 76.00 79.00 73.30 69.69 64.90 28.70 27.79
0.680 0.675 0.696 0.675 0.661 0.697 0.694 0.776 0.771 0.790 0.690 0.487 0.463 0.494 0.469 0.494 0.474 0.458 0.437 0.458 0.466 0.487 0.478 0.487 0.466 0.538 0.511 0.538 0.488 0.560 0.520 0.490 0.500 0.479 0.427 0.433 0.431 0.478 0.478 0.478 0.470 0.379 0.372 0.379 0.366 0.420 0.440 0.766 0.806
From Payne [15]. The half of all data sets used showing the least growth.
2
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12 12 22 22 32 32 42 42 52 52 6 62 7 7 82 82 9 9 122 122 142 142 152 152 162 162 172 172 182 182 192 192 202 202 212 212 22 22 232 232 242 242 25 25 26 26 27 27 282 282 292 292 302 302 312
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Table 3. Comparison of ANOVA results for gain and feed utilization efficiency (g of gain/g of feed) from different models Source of variation
df
SE of estimate
Pr > |t|
92.7689 −2.51556
12.5099 0.62610
<0.0001 0.0001
30.0526 0.2918
2.0625 0.0725
<0.0001 <0.0001 <0.0001
0.2029 0.0211
0.0816 0.0041
0.0145 <0.0001
0.6371 0.0041
0.0287 0.0010
<0.0001 0.0002 0.0037
R2 0.137
0.997
0.208
0.987
1
Pr = probability.
PROC GLM; model BWG FE = CP, and PROC GLM; class EXPT; BWG FE = CP EXPT, where BWG is daily BW gain (g/d), FE is feed efficiency (g of gain/g of consumption), CP is dietary CP level (%), and EXPT is experiment.
RESULTS If the gain data are analyzed as a simple collection of data points from the literature without regard for the individual experiments from which they came, CP is a very highly significant contributor to the variation in BW gain (Table 3 and Figure 2), and CP has a negative effect on BW gain (it is toxic). If each experiment from which the data came is also included in the analysis, CP is again a significant contributor to the variation in BW gain, but the coefficient is positive (Table 3 and Figure 3). Each unit (percentage) of protein increased daily BW gain (g) by 0.2918 ± 0.0724. A total of 71.2% of the data sets had positive slopes for BW gain as a function of dietary CP level. If the FE data are analyzed as a simple collection of data from the literature without regard
for the individual experiments from which they came, CP is a very highly significant contributor to the variation in FE (Table 3 and Figure 4), and CP has a positive effect on FE (G:F). If each experiment from which the data came is also included in the analysis, CP is again a significant contributor to the variation in FE, and the coefficient is again positive (Table 3). Each unit (percentage) of protein increased FE by 0.0041 ± 0.0010. A total of 75.0% of the data sets had positive slopes for FE as a function of dietary CP level.
Figure 2. The relationship between ADG and dietary protein level (PL). Holistic analysis of data from 52 experiments. Model: ADG = f(PL).
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ADG as a function of CP level (CP, %) Intercept 1 CP 1 Error 102 ADG as a function of CP level (CP, %) and experiment Intercept 1 CP 1 Experiment 51 Error 52 Feed utilization as a function of CP level (CP, %) 1 Intercept 1 CP 102 Error Feed utilization as a function of CP level (CP, %) and experiment 1 Intercept 1 CP 51 Experiment Error 52
Parameter estimate
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These results make it clear that CP level is still a significant contributor to variation in both broiler growth and FE, even when purified amino acids are added to the lower CP feeds (from the collection of data in Table 2). The BW responses in Figure 3 are still increasing, similar to the BW responses in Figure 1 (between 100 and 110% of manual recommendations). Similarly, the FE responses in Figure 4 are increasing, similar to the FE responses in Figure 1 (between 90 and 100% of manual recommendations). The overall conclusion from the data set compiled by Payne [15] should be that both amino acid supplementation and CP levels are important in determining growth responses of broilers (at least in the ranges studied). The conclusions of Payne [15] are quite correct from the perspective of exam-
Figure 4. The relationship between FE and dietary protein level (PL). Holistic analysis of data from 26 experiments with the highest daily gains. Model: FE = f(PL).
Figure 3. The relationship between ADG and dietary protein level (PL). Holistic analysis of 52 experiments (EXP). Model: ADG = f(PL, EXP).
When only the data from the 26 research trials with birds with the lowest BW gains were considered, no significant effects of protein level on BW gain (P < 0.2830) or FE (P < 0.1693) were observed. However, when only the data from the 26 research trials with birds with the highest BW gains were considered, highly significant effects of protein level on BW gain (P < 0.0001) and FE (P < 0.0001) were observed (the independent variable “experiment” was included in the models). Each unit (percentage) of protein increased daily BW gain (g) by 0.6061 ± 0.1063 and FE by 0.0072 ± 0.0120. A total of 82.8% of the data sets had positive slopes for BW gain as a function of dietary CP level.
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DISCUSSION
ining whether 2 points in each experiment can be declared as significantly different at P < 0.05. The problem is that each experiment should come with a disclaimer stating that “because of variability in the data, differences smaller than some percentages could not reliably be detected.” Finding no significant differences should not be taken to mean that no differences existed. By pooling the data as in Table 3, it becomes clear that CP level really is having some significant effect overall (P < 0.0001 for gain, and P = 0.0002 for feed utilization efficiency). Whether that effect is important is an economic question: Is the cost of additional protein offset by the increased BW, breast meat yield, and so forth? That is not to imply that all the experiments listed in Table 2 would have shown significant responses to BW and feed utilization efficiency had there been adequate replication. Body weight gain and FE slopes, for instance, approach zero in the interval from 110 to 120% of manual CP recommendations in Figure 1. Had the experiments been conducted in this range, certainly it would have been extremely difficult to declare any differences as significant with the resources most researchers have to provide replication. Breast meat and eviscerated yield for both sexes and abdominal fat for females, however, still showed linear changes in the manual CP recommendations at 110 to 120% and need to be considered even though BW and FE are not changing in any detectable amounts. Whether significant differences can be detected depends on several factors, including 1)
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dom from 102 to 51. However, 51 df is still adequate to show that ADG and CP are related (less than 2 chances in 10,000 that observed effects are due to chance). The R2 values, the amount of variation described by the experimental model, increases from 0.137 to 0.997 when the effect of experiment is accounted for. Clearly, most of the variation in the ADG data in this data set is due to experimental variables other than dietary CP level. When differences in experiment are accounted for in the statistical model, ADG appears to be directly proportional to percentage of CP (positive coefficient for percentage of CP; Table 3 and Figure 2) in the ranges studied. The slower growing birds may not have shown responses to CP for several reasons: 1) they may simply have been younger and so may have responded differently physiologically; 2) their environmental (growing) conditions may have been such that they were not near their genetic potential; or 3) they may have been of specific genetic stocks that showed little growth response to dietary CP level in the ranges being studied. The NRC [1] emphasized the increasing importance of developing comprehensive models: Generally, as dietary protein level increases, essential amino acid requirements (expressed as a percentage of the diet) increase, although when expressed as a percentage of the protein, essential amino acid requirements are little affected. . . . These observations demonstrate the importance of maintaining a balance among the concentrations of essential and nonessential amino acids in poultry diets. Optimal balance is important for efficient utilization of dietary protein. The protein and amino acid concentrations presented as requirements herein are intended to support maximum growth and production. Achieving maximum growth and production, however, may not always ensure maximum economic returns, particularly when prices of protein sources are high. If decreased performance can be tolerated, dietary concentrations of amino acids may, accordingly, be reduced somewhat to maximize economic returns.
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the growth rate of the birds, 2) the quality (digestibility) of the ingredients, 3) the magnitude of the CP reduction, 4) the amount of experimental variation, and 5) the number of replicates per treatment. The more imbalanced a feed is to begin with, because of the individual ingredients and their qualities, the greater will be the detectable differences in protein level. When more is known about ingredient quality, such as individual amino acid digestibilities, then better amino balances can be achieved and more of the essential amino acids will be incorporated into body protein and less will be oxidized and metabolized. The approach taken in the experiments whose results are summarized in Table 3 and Figures 2 to 4 does not directly address the questions of 1) what the ratio of essential to nonessential amino acids should be, or 2) what the response is to total essential and nonessential amino acids (CP). Collectively, the results suggest little response to dietary protein level in the younger and slower growing birds. This is consistent with recommendations of relatively high protein levels when birds are young and growing at slow (absolute g/d) rates. However, when birds are older and growing at faster rates, the protein levels fed were limiting growth and feed utilization efficiency in the majority of cases, resulting in very high probabilities that the observed differences were not due to chance. In experiments showing the responses to protein level (despite the lower protein diets being better balanced), the real consideration should be, “Is the cost of the additional protein at least offset by the additional returns from increased growth rate or less feed per unit of salable product?” These analyses illustrate several potential problems that may occur when analyzing data sets made from a collection of results from experiments with many design differences. The initial analysis simply relating all ADG = f (CP) (Table 3 and Figure 2) suggests that CP is toxic in the range studied (note the negative coefficient for CP in Table 3). This apparent relationship may simply be due to the different experimental conditions used: younger chicks tend to be fed higher CP levels but naturally have lower ADG. Including “experiment” in the regression model (Table 3) lowers error degrees of free-
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Pesti: AMINO ACIDS AND CRUDE PROTEIN
CONCLUSIONS AND APPLICATIONS
1. The choice of the appropriate statistical model is critical to making appropriate conclusions about the relationship between dietary protein level, amino acid supplementation, and broiler performance. 2. Although individual experiments may seem to show no “significant” response to dietary protein level (even with amino acid supplementation), when the data are pooled with an appropriate regression model, clear responses to dietary protein are obvious and are highly significant. 3. Essential amino acid balance and total amino acid levels (CP or essential plus nonessential amino acids) should be considered to optimize growth and to maximize profits. Simply lowering CP levels by supplementing amino acids may not result in maximum performance or profits.
REFERENCES AND NOTES 1. NRC. 1994. Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 2. Almquist, H. J. 1947. Evaluation of amino acid requirements by observations on the chick. J. Nutr. 34:543– 563.
3. Almquist, H. J. 1952. Amino acid requirements of chickens and turkeys—A review. Poult. Sci. 31:966 –981. 4. Boomgaardt, J., and D. H. Baker. 1971. Tryptophan requirement of growing chicks as affected by dietary protein level. J. Anim. Sci. 33:595–599. 5. Boomgaardt, J., and D. H. Baker. 1973. The lysine requirement of growing chicks fed sesame meal-gelatin diets at three protein levels. Poult. Sci. 52:586–591. 6. Morris, T. R., K. Al-Azzawi, R. M. Gous, and G. L. Simpson. 1987. Effects of protein concentration on responses to dietary lysine by chicks. Br. Poult. Sci. 28:185–195. 7. Mendonca, C., and L. S. Jensen. 1989. Influence of protein concentration on the sulfur-containing amino acid requirement of broiler chickens. Br. Poult. Sci. 30:889– 898. 8. Leclercq, B. 1983. The influence of dietary protein content on the performance of genetically lean or fat growing chickens. Br. Poult. Sci. 24:581–587. 9. Leclercq, B., and G. Guy. 1991. Further investigations on protein requirement of genetically lean and fat chickens. Br. Poult. Sci. 32:789–798. 10. Alleman, F., J. Michel, A. M. Chagneau, and B. Leclercq. 2000. The effects of dietary protein independent of essential amino acids on growth and body composition in genetically lean and fat chickens. Br. Poult. Sci. 41:214–218. 11. Smith, E. R., G. M. Pesti, R. I. Bakalli, G. O. Ware, and J. F. M. Menten. 1998. Further studies on the influence of genotype and dietary protein on the performance of broilers. Poult. Sci. 77:1678–1687. 12. Smith, E. R., and G. M. Pesti. 1998. Influence of broiler strain cross and dietary protein on the performance of broilers. Poult. Sci. 77:276–281. 13. Aviagen. 2000. Broilers, Protein and Profit. Ross Tech. 00/39. Aviagen, Newbridge, Midlothian, Scotland, UK. 14. Emmert, J. L., and D. H. Baker. 1997. Use of the ideal protein concept for precision formulation of amino acid levels in broiler diets. J. Appl. Poult. Res. 6:462–470. 15. Payne, R. L. 2007. The potential for using low crude protein diets for broilers and turkeys. Degussa AminoNews 8:2–13. 16. Aletor, V. A., I. I. Hamid, and E. Pfeffer. 2000. Low protein amino acid-supplemented diets in broiler chickens: Effects on performance, carcass characteristics, whole-body composition and efficiencies of nutrient utilization. J. Sci. Food Agric. 80:547–554. 17. Bregendahl, K., J. S. Sell, and D. R. Zimmerman. 2002. Effect of low protein diets on growth performance and body composition of broiler chicks. Poult. Sci. 81:1156– 1167. 18. Brooks, S. E., H. M. Allen, and J. D. Firman. 2003. Utilization of low crude protein diets fed to 0–3 wk broilers. Poult. Sci. 82(Suppl. 1):37. (Abstr.) 19. Cabel, M. C., and P. W. Waldroup. 1991. Effect of dietary protein level and length of feeding on performance and abdominal fat pad content of broiler chickens. Poult. Sci. 70:1550–1558. 20. Corzo, A., M. T. Kidd, D. J. Burnham, and B. J. Kerr. 2004. Dietary glycine needs of broiler chicks. Poult. Sci. 83:1382–1384. 21. Fancher, B. I., and L. S. Jensen. 1989. Dietary protein level and essential amino acid content: Influence upon female broiler performance during the grower period. Poult. Sci. 68:897–908.
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Clearly, it is becoming more important not to waste dietary CP from both cost and environmental waste perspectives. Amino acid supplementation is one key factor in reducing CP levels in practical broiler feeds (Table 1). Optimizing, and not minimizing, CP levels is another. The idea of comparing low CP plus nonessential amino acids with some higher standard implies that the goal of feed formulation is merely to achieve some standard performance. However, it is just as clear that feed formulation should have as its goal achieving a compromise between diet cost and performance. Performance increasingly means optimizing eviscerated and breast meat yields, not just maximizing BW and FE. The emphasis of amino acid and protein research should be on developing equations that can be used to relate inputs (costs) and outputs (performance) to maximize profits under various environmental conditions with each genetic stock.
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1999. Ideal amino acid profile and dietary lysine specification for broiler chickens of 20 to 40 days of age. Br. Poult. Sci. 40:257–265. 31. Parr, J. F., and J. D. Summers. 1991. The effect of minimizing amino acid excesses in broiler diets. Poult. Sci. 70:1540–1549. 32. Pesti, G. M., and C. F. Smith. 1984. The response of growing broiler chickens to dietary protein, energy and added fat contents. Br. Poult. Sci. 25:127–138. 33. Pinchasov, Y., C. X. Mendonca, and L. S. Jensen. 1990. Broiler chick response to low protein diets supplemented with synthetic amino acids. Poult. Sci. 69:1950– 1955. 34. Robbins, K. R. 1987. Threonine requirement of the broiler chick as affected by protein level and source. Poult. Sci. 66:1531–1534. 35. Schutte, J. B., W. Smink, and M. Pack. 1997. Requirement of young broiler chicks for glycine + serine. Arch. Geflugelkd. 61:43–47. 36. Si, J., C. A. Fritts, P. W. Waldroup, and D. J. Burnham. 2004. Effects of tryptophan to large neutral amino acid ratios and overall amino acid levels on utilization of diets low in crude protein by broilers. J. Appl. Poult. Res. 13:570–578. 37. Si, J., C. A. Fritts, P. W. Waldroup, and D. J. Burnham. 2004. Effects of excess methionine from meeting needs for sulfur amino acids on utilization of diets low in crude protein by broiler chicks. J. Appl. Poult. Res. 13:579–587. 38. Waldroup, P. W. 2000. Feeding programs for broilers: The challenge of low protein diets. Pages 119–134 in Proc. 47th Annu. Maryland Nutr. Conf. Maryland Feed Ind. Counc. Inc., College Park, MD. 39. SAS Institute. 2001. SAS User’s Guide: Statistics. Version 8.02 Edition. SAS Inst. Inc., Cary, NC.
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22. Fancher, B. I., and L. S. Jensen. 1989. Male broiler performance during the starting and growing periods as affected by dietary protein, essential amino acids, and potassium levels. Poult. Sci. 68:1385–1395. 23. Ferguson, N. S., R. S. Gates, J. L. Taraba, A. H. Cantor, A. J. Pescatore, M. L. Straw, M. J. Ford, and D. J. Burnham. 1998. The effect of dietary protein and phosphorus on ammonia concentration and litter composition in broilers. Poult. Sci. 77:1085–1093. 24. Ferguson, N. S., R. S. Gates, J. L. Taraba, A. H. Cantor, A. J. Pescatore, M. L. Straw, M. J. Ford, and D. J. Burnham. 1998. The effect of dietary crude protein on growth, ammonia concentration and litter composition in broilers. Poult. Sci. 77:1481–1487. 25. Fritts, C. A., A. Corzo, and M. T. Kidd. 2004. Chick responses to diets differing in essential and nonessential amino acids. Poult. Sci. 83(Suppl. 1):443. (Abstr.) 26. Han, Y., H. Suzuki, C. M. Parsons, and D. H. Baker. 1992. Amino acid fortification of a low protein corn and soybean meal diet for chicks. Poult. Sci. 71:1168–1178. 27. Heger, J., and M. Pack. 1996. Effects of dietary glycine + serine on starting broiler chick performance as influenced by dietary crude protein levels. Agribiol. Res. 49:257–265. 28. Kerr, B. J., and M. T. Kidd. 1999. Amino acid supplementation of low-protein broiler diets: 1. Glutamic acid and indispensable amino acid supplementation. J. Appl. Poult. Res. 8:298–309. 29. Kerr, B. J., and M. T. Kidd. 1999. Amino acid supplementation of low-protein broiler diets: 2. Formulation on an ideal amino acid basis. J. Appl. Poult. Res. 8:310–320. 30. Mack, S., D. Bercovici, G. de Groote, B. Leclercq, M. Lippens, M. Pack, J. B. Schutte, and S. vanCauwenberghe.
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