Assessment of Dietary Rovabio Excel in Practical United States Broiler Diets

Transcription

1 2007 Poultry Science Association, Inc. Assessment of Dietary Rovabio Excel in Practical United States Broiler Diets M. L. West,* A. Corzo,* W. A. Dozier III, M. E. Blair, and M. T. Kidd* *Department of Poultry Science, Mississippi State University, Mississippi State 39762; Agriculture Research Service, USDA, Mississippi State 39762; and Addisseo, Alpharetta, Georgia Primary Audience: Nutritionists, Researchers, Feed Manufacturers SUMMARY The focus of this study was to evaluate a feed enzyme (Rovabio Excel) in diets fed to commercial broilers reared in environments typical to that observed in the US broiler industry and destined to be marketed at BW at or near 2.5 kg. The feed enzyme was tested in diets differing in amino acid and energy composition. The main effect of altered nutrient levels, mainly reduced amino acids, was higher abdominal fat at processing. The formulation addition of the exogenous feed enzyme to diets differing in nutrient contents and energy did not affect broiler live performance or carcass traits. However, the exogenous feed enzyme decreased 14-d mortality in experiment 1 and 41-d mortality in experiment 2 but was without effect on mortality in experiment 3. Future research elucidating any benefits on mortality from the exogenous feed enzyme may aid commercial poultry producers. Further, reducing dietary nutrient levels beyond that considered in this study may allow for exogenous enzyme benefits in broiler live production and carcass traits to be observed as mediated through nutrient liberation. Key words: xylanase, β-glucanase, cellulase, amino acid, energy, broiler, nutrient density 2007 J. Appl. Poult. Res. 16: DESCRIPTION OF PROBLEM Recent trends in energy prices in the United States have raised public and congressional awareness concerning alternative energy sources. As production of alternative energy sources (i.e., biodiesel and ethanol) is increased, commodity pricing of energy-contributing ingredients (e.g., corn and oil sources) may be affected. Because some enzymes are known to liberate energy- and protein-contributing nutrients, this research encompasses 3 experiments evaluating the effect of an exogenous feed enzyme (Rovabio [1]) supplemented to broiler diets primarily based on corn, soybean meal, and poultry oil. Rovabio (ROV) is a concentrated enzyme (from the same organism and fermentation) solution primarily containing xylanase and β-glucanase obtained from a fermentation broth of Penicillium funiculosum. Evidence exists that improved gut health effects of some enzymes may be heightened when exogenous enzymes are fed in combination [2]. The manufacturing company suggests that ROV could improve energy digestibility from 2 to 6% and enhance amino acid digestibility from 1 to 2% [3]. Cowieson et al. [4] found that nutrient digestibility of broilers fed corn and soybean meal diets was increased by a combination of xylanase, amylase, protease, and phytase. The former findings have been 1 Corresponding author: mkidd@poultry.msstate.edu

2 314 JAPR: Research Report Table 1. Ingredients and calculated composition of experimental diets fed to broilers in experiment 1 1 1to14d 15to31d 32to42d Ingredients Control Downspec Control Downspec Control Downspec Yellow corn Soybean meal Poultry fat Dicalcium P Limestone NaCl Premix DL-Met L-Lys HCl L-Thr Sacox Calculated composition 4 CP, % ME, kcal/kg 3,050 2,984 3,100 3,034 3,150 3,084 Lys, % TSAA, % Thr, % Ca, % Available P, % Na, % Choline, mg/kg 1,550 1,550 1,450 1,450 1,400 1,400 1 Four treatments were implemented in each experimental period: 1) control diet; 2) control diet + Rovabio; 3) downspec: 30 kcal/lb of ME and amino acid levels of 2.5% amino acids; and 4) downspec: 30 kcal/lb of ME and amino acid levels of 2.5% amino acids + Rovabio. Rovabio (0.200 L) was suspended into 1.5 L of potable water and sprayed onto pelleted feed. 2 Premix provided the following per kilogram of diet: retinyl acetate, 2,654 g; cholecalciferol, 110 g; DL-α-tocopherol acetate, 9.9 mg; menadione, 0.9 mg; B 12, 0.01 mg; folic acid, 0.6 g; choline, 379 mg; D-pantothenic acid, 8.8 mg; riboflavin, 5.0 mg; niacin, 33 mg; thiamin, 1.0 mg; D-biotin, 0.1 mg; pyridoxine, 0.9 mg; ethoxyquin, 28 mg; Mn, 55 mg; Zn, 50 mg; Fe, 28 mg; Cu, 4 mg; I, 0.5 mg; and Se, 0.1 mg. 3 Sacox represents 60 g/short ton of salinomycin sodium. 4 Digestible amino acids. shown when the corn and soybean meal diets fed to broilers were marginal in nutrient needs [5]. Most research that has been conducted with β-glucanase and xylanase has been done with barley- or wheat-based diets. For example, Vukic Vranjes and Wenk [6] studied the effects of enzyme preparations of β-glucanase and xylanase in broiler diets containing barley and found that the enzyme preparation improved broiler live production traits in addition to increasing energy, fat, and N utilization and DM content of excreta. Due to the lack of published research evaluating the effect of ROV on broiler chickens fed corn-soybean meals diets, 3 experiments were conducted to assess the effect on growth and carcass responses in commercial broilers reared in floor pen environments. The objective of this research was to test the effect of ROV on birds destined for the 2.5- kg market. In experiment 1, a control diet was compared with a downspec diet with lowered ME and amino acid levels each with and without ROV. In experiments 2 and 3, a control diet (100) was fed that mimicked industry ingredient and nutrient levels. The essential amino acid composition was increased by 5% (105, experiment 2) or 10% (110, experiments 2 and 3), because many broiler integrators are increasing amino acid density to increase yields. The diets in experiments 2 and 3 were fed with and without ROV. MATERIALS AND METHODS Experimental Facility and Bird Husbandry All birds received a Marek s vaccination at d 18 in ovo and Newcastle and infectious bronchitis vaccines via spray cabinet at hatch. After

3 WEST ET AL.: DIET DENSITY AND ENZYME ADDITION 315 Table 2. Ingredients and calculated composition of experimental diets fed to broilers in experiment 2 1 1to14d 15to32d 33to40d Ingredients Yellow corn Soybean meal Poultry meal Poultry fat Dicalcium P Limestone NaCl Premix DL-Met L-Lys HCl Sacox Choline L-Thr Calculated composition 4 CP, % ME, kcal/kg 3,100 3,100 3,100 3,140 3,140 3,140 3,180 3,180 3,180 Lys, % TSAA, % Thr, % Ile, % Ca, % Available P, % Na, % Choline, mg/kg 1,550 1,550 1,550 1,475 1,475 1,475 1,400 1,400 1,400 1 Six treatments were implemented in each experimental period: 1) 100: control diet; 2) 100: control diet + Rovabio; 3) 105: 5% increase in amino acids; 4) 105: 5% increase in amino acids + Rovabio; 5) 110: 10% increase in amino acids; and 6) 110: 10% increase in amino acids + Rovabio. Rovabio (0.200 L) was suspended into 1.5 L of potable water and sprayed onto pelleted feed. 2 Premix provided the following per kilogram of diet: retinyl acetate, 2,654 g; cholecalciferol, 110 g; DL-α-tocopherol acetate, 9.9 mg; menadione, 0.9 mg; B 12, 0.01 mg; folic acid, 0.6 g; choline, 379 mg; D-pantothenic acid, 8.8 mg; riboflavin, 5.0 mg; niacin, 33 mg; thiamin, 1.0 mg; D-biotin, 0.1 mg; pyridoxine, 0.9 mg; ethoxyquin, 28 mg; Mn, 55 mg; Zn, 50 mg; Fe, 28 mg; Cu, 4 mg; I, 0.5 mg; and Se, 0.1 mg. 3 Sacox represents 60 g/short ton of salinomycin sodium. 4 Digestible amino acids. transportation to the research unit, chicks were feather-sexed, weighed, wing-tagged, and assigned to floor pens. Each floor pen contained a line of nipple drinkers and a tube feeder. Feed and water was administered ad libitum. The birds were placed on used softwood shavings. Experiment 1 utilized 1,472 Ross Ultra-Yield Hubbard commercial broilers [7] allocated in 32 pens of 23 males and 23 females each. Experiment 2 utilized 576 Ross Ultra-Yield Hubbard commercial male broilers [7] allocated in 48 pens of 12 males. Experiment 3 utilized 360 Ross 708 commercial male broilers [8] allocated in 30 pens of 12 males each. Experimental Design and Diets The enzyme preparations in all experiments were added after diets were pelleted to ensure that enzyme activity would not be reduced. Feed samples of each batch of feed were randomly tested using a colorimetric enzyme test kit for the presence or absence of ROV. All tests were evaluated and confirmed as positive for enzyme activity before the feed was weighed into feeders in the experimental facility. Experiment 1. Birds were fed 4 dietary treatments (8 replications/treatment) in 3 periods consisting of varying levels of CP, AME, and amino acids (Table 1). The periods consisted of 1 to 14, 15 to 31, and 32 to 42 d of age. The first diet was a control diet. The second diet was the control diet with ROV added, postpelleting at the rate of 0.022%. The third diet had lower nutrient density, containing less CP (0.5% less), less energy (66 kcal/kg), and less essential amino acid levels (about 2.5%). The fourth diet was

4 316 JAPR: Research Report Table 3. Ingredients and calculated composition of experimental diets fed to broilers in experiment 3 1 1to14d 15to33d 34to49d Ingredients Yellow corn Soybean meal Poultry meal Poultry fat Dicalcium P Limestone NaCl Premix DL-Met L-Lys HCl Sacox Choline L-Thr Calculated composition 4 CP, % ME, kcal/kg 3,100 3,100 3,140 3,140 3,180 3,180 Lys, % TSAA, % Thr, % Ile, % Ca, % Available P, % Na, % Choline, mg/kg 1,550 1,550 1,475 1,475 1,400 1,400 1 Three treatments were implemented in each experimental period: 1) 100: control diet; 2) 100: control diet + Rovabio; 3) 110: 10% increase in amino acids. Rovabio (0.200 L) was suspended into 1.5 L of potable water and sprayed onto pelleted feed. 2 Premix provided the following per kilogram of diet: retinyl acetate, 2,654 g; cholecalciferol, 110 g; DL-α-tocopherol acetate, 9.9 mg; menadione, 0.9 mg; B 12, 0.01 mg; folic acid, 0.6 g; choline, 379 mg; D-pantothenic acid, 8.8 mg; riboflavin, 5.0 mg; niacin, 33 mg; thiamin, 1.0 mg; D-biotin, 0.1 mg; pyridoxine, 0.9 mg; ethoxyquin, 28 mg; Mn, 55 mg; Zn, 50 mg; Fe, 28 mg; Cu, 4 mg; I, 0.5 mg; and Se, 0.1 mg. 3 Sacox represents 60 g/short ton of salinomycin sodium. 4 Digestible amino acids. the same as the third diet with ROV added, postpelleting at 0.022%. Justification for the diet reductions was based on current recommendations [3]. Supplemental feeder lids were used from 1 to 10 d to ensure access to feed. Experiment 2. Birds were fed 6 dietary treatments (8 replications/treatment) in 3 periods consisting of varying levels of amino acids (Table 2). The periods consisted of 1 to 14, 15 to 32, and 33 to 40 d of age. The treatment design consisted of a 2 (ROV) 3 (amino acid density) factorial arrangement. The ROV treatments consisted of either water (1.5 L) or 0.022% ROV with water to the weight of 1.5 L sprayed on the feed postpelleting. The dietary treatments represented a control diet formulated to mimic industry amino acid levels (100%). Dietary amino acids were then increased by 5 and 10% to derive 2 additional treatments (105 and 110%). The 100% amino acid density diet mimicked regimes observed by some integrators that feed for optimal breast meat yield. Energy and all other nutrients were equal in all diets. Experiment 3. Birds were fed 3 dietary treatments (10 replications/treatment) in 3 periods (Table 3). The periods consisted of 1 to 14, 15 to 33, and 34 to 49 d of age. The first diet was a control diet. The second diet was the control diet with ROV added at 0.022%. The third diet consisted of a 10% increase in amino acid levels. Measurements Body weight, feed intake, and feed conversion measurements were taken at d 1 and at the end of each feeding period. Mortality was collected daily, and the weight of dead birds was

5 WEST ET AL.: DIET DENSITY AND ENZYME ADDITION 317 Table 4. Live performance measurements of male broilers as affected by diet density and Rovabio Excel feed enzyme fed from 1 to 42 d (experiment 1) 1 1to14d 1to31d 1to42d BW gain FCR 2 Mortality BW gain FCR 2 Mortality BW gain FCR 2 Mortality Diet Rovabio (kg) (kg:kg) (%) (kg) (kg:kg) (%) (kg) (kg:kg) (%) Control a 1.67 b Downspec b 1.74 a SEM SEM Diet Rovabio Diet Rovabio a,b Means with no common superscripts within a column differ (P < 0.05). 1 Four treatments were implemented in each experimental period: 1) control diet; 2) control diet + Rovabio; 3) downspec diet ( 30 kcal/lb of ME and amino acid levels of 2.5% AA); and 4) downspec diet ( 30 kcal/lb of ME and amino acid levels of 2.5% AA) + Rovabio. +/ = Diets with or without Rovabio, respectively. 2 Values expressed were adjusted for mortality. recorded. Feed intake was corrected for mortality to adjust feed conversion. All birds were weighed individually at d 42 to calculate uniformity in experiment 1 only. Carcass measurements were taken at the end of each period in all experiments [320 birds or 10 birds/pen (5 of each sex) in experiment 1; 384 birds or 8 birds/ pen in experiment 2; 150 birds or 5 birds/pen in experiment 3]. Live bird weight was obtained from each pen. Feed was withdrawn 12 h before slaughter. Birds were placed into coops and transported to the processing facility. Birds were manually hung on shackles, stunned with an electric knife, bled for 3 min after the jugular vein was severed, scalded for 45 s, and defeathered in a rotary picker for 2 min. Hocks and heads were removed manually, followed by rehanging of birds on an automated shackle line. Viscera and abdominal fat were then removed manually. Carcass and abdominal fat weights were recorded. Carcasses were washed and placed into an ice bath for 4 h. Carcasses were individually placed on a manual deboning line, and breast muscles (pectoralis major and pectoralis minor) were removed from the carcass, weighed, and recorded in experiments 1 and 3 only. Weights for each variable measured were expressed as absolute weights and relative to live BW at processing. Statistical Analysis In experiments 1 and 2, a randomized complete block design was used. A completely randomized design was used in experiment 3. Pen was used as the experimental unit in all experiments. In experiments 1 and 2, the 4 and 6 treatments, respectively, of the factorial arrangement of treatments were analyzed by the GLM procedure of SAS [9]. Data in experiment 3 were analyzed using the GLM procedure of SAS [9]. Means were tested for significant differences using the least-squares means option of SAS [9] using α = Arcsine transformation was used on mortality [10]. RESULTS AND DISCUSSION Differences in uniformity as measured in experiment 1 did not occur (data not shown). Live performance results of experiment 1 are presented in Table 4. There was a significant diet effect (P 0.002) on BW at d 31. Body weight was improved in birds fed the control diet over birds fed the downspec diet. There was a significant dietary improvement (P 0.001) in 31- d feed conversion in birds fed the control diet. The dietary treatments with or without ROV Excel did not significantly affect BW, feed conversion, or mortality.

6 318 JAPR: Research Report Table 5. Live performance measurements of male broilers as affected by dietary amino acid density and Rovabio Excel feed enzyme fed from 1 to 40 d (experiment 2) 1 1to14d 1to32d 1to40d BW gain FCR 2 Mortality BW gain FCR 2 Mortality BW gain FCR 2 Mortality Diet Rovabio (kg) (kg:kg) (%) (kg) (kg:kg) (%) (kg) (kg:kg) (%) a a a a b b 4.7 SEM SEM Diet Rovabio Diet Rovabio a,b Means with no common superscripts within a column differ (P < 0.05). 1 Six treatments were implemented in each experimental period: 1) control diet; 2) control diet + Rovabio; 3) 5% increase in amino acids; 4) 5% increase in amino acids + Rovabio; 5) 10% increase in amino acids; and 6) 10% increase in amino acids + Rovabio. +/ = Diets with or without Rovabio, respectively. 2 Values expressed were adjusted for mortality. Live performance results of experiments 2 and 3 are presented in Tables 5 and 6, respectively. There was a significant dietary effect on 32-d feed conversion (experiment 2). The high amino acid diet significantly reduced the 32- and 40-d feed conversion compared with birds fed the control and moderate amino acid density diet. This is also in agreement with research done by Corzo et al. [11] and Kidd et al. [12] demonstrating the positive effect of higher amino acid levels on decreasing feed conversion. The dietary treatments, with or without ROV, did not significantly affect BW or mortality. Total mortality did not significantly differ in any experiment. However, dietary ROV reduced 14-d mortality (P = 0.06) in experiment 1 and 40-d mortality (P = 0.06) in experiment 2 as in agreement with Engberg et al. [13]. The reduction in mortality in experiment 1 to ROV occurred in birds fed the downspec diet (control diet without ROV = 1.9% mortality; control diet with ROV = 2.4% mortality; downspec diet without ROV = 3.0% mortality; downspec diet with ROV = 0.0% mortality). Mortality in the experiments averaged 3.68% (experiment 1, Ross Hubbard Ultra-Yield), 4.95% (experi- Table 6. Live performance measurements of male broilers as affected by dietary amino acid density and Rovabio Excel feed enzyme fed from 1 to 49 d (experiment 3) 1 1to14d 1to33d 1to49d BW gain FCR 2 Mortality BW gain FCR 2 Mortality BW gain FCR 2 Mortality Diet (kg) (kg:kg) (%) (kg) (kg:kg) (%) (kg) (kg:kg) (%) SEM Treatment Three treatments were implemented in each experimental period: 1) control diet (100 ); 2) control diet + Rovabio (100+); and 3) 10% increase in amino acids (110). 2 Values expressed were adjusted for mortality.

7 WEST ET AL.: DIET DENSITY AND ENZYME ADDITION 319 Table 7. Processing measurements of 42-d-old male broilers as affected by dietary amino acid density and Rovabio Excel feed enzyme fed from 1 to 42 d (experiment 1) 1 Abdominal fat Carcass 2 Breast meat yield 3 Weight Yield Weight Yield Weight Yield Diet Rovabio (kg) (% of BW) (kg) (% of BW) (kg) (% of BW) Control b 1.79 b Downspec a 1.93 a SEM SEM Diet Rovabio Diet Rovabio a,b Means with no common superscripts within a column differ (P < 0.05). 1 Four treatments were implemented in each experimental period: 1) control diet; 2) control diet + Rovabio; 3) downspec diet ( 30 kcal/lb of ME and amino acid levels of 2.5% AA); and 4) downspec diet ( 30 kcal/lb of ME and amino acid levels of 2.5% AA) + Rovabio. +/ = Diets with or without Rovabio, respectively. 2 Represents eviscerated carcass without feet, shanks, and head but with neck. 3 Represents pectoralis major and minor. ment 2, Ross Hubbard Ultra-Yield), and 10.97% (experiment 3, Ross Ross 708). Environmental and managerial differences did not appear to contribute to mortality variations. Broilers in experiment 3 were grown to heavier weights than experiments 1 and 2. Broilers in experiment 3 were not necropsied to determine the cause for high mortality. Nevertheless, the effect of dietary ROV Excel should be further studied in broilers fed corn and soybean mealbased diets. Moreover, as commodity pricing of energy-contributing ingredients increases, larger decreases in energy values should be implemented in further ROV trials. Processing results from experiments 1, 2, and 3 are presented in Tables 7, 8, and 9, respectively. Dietary treatment interactions did not occur in any of the experiments. Dietary treatments responded the same in experiments 1, 2, and 3 in regards to when amino acid density was reduced, but fat weight and percentage significantly increased. However, the decrease in abdominal fat weight observed in experiment 3 as achieved by increasing amino acid density (110) was not significant (P = 0.135). This also agrees with research done by Corzo et al. [11] and Kidd et al. [12] indicating the positive effect of amino acid density on lean tissue vs. fat accretion. Dietary treatments did not influence carcass weight or yield in any of the trials. Breast meat yield was not affected by the dietary treatments in experiments 1 or 3. There was no significant difference in any of the ROV treatments; however, there were some trends shown. It may be that the downspec diets were not reduced to levels to produce measurable nutrient limitation effects in the experimental facility used herein. Further experiments should be conducted using lower amino acid levels to determine if ROV could improve live performance and yield as mediated through increased nutrient liberation. There is little published research evaluating xylanase, β-glucanase, and cellulase in cornbased diets in commercial broilers. Most of the research has been done on wheat- or barleybased diets. However, certain enzyme combinations in corn and soybean meal-based diets (i.e., xylanase, amylase, protease, and phytase) have been noted to increase nutrient availability, especially when the diets are marginal in nutrient needs [4, 5]. It may be, however, that the nutrient levels tested herein were above the needs of the birds, rendering results on ROV to be somewhat inconclusive. Hence, future research should address the efficacy of ROV in diets marginal in nutrients, whereas improvements in nutrient utilization could be realized, because the above

8 320 JAPR: Research Report Table 8. Processing measurements of 41-d-old male broilers as affected by dietary amino acid density and Rovabio Excel feed enzyme fed from 1 to 40 d (experiment 2) 1 Abdominal fat Carcass 2 Weight Yield Weight Yield Diet Rovabio (kg) (% of BW) (kg) (% of BW) a 1.74 a b 1.57 b c 1.43 c SEM SEM Diet Rovabio Diet Rovabio a c Means with no common superscripts within a column differ (P < 0.05). 1 Six treatments were implemented in each experimental period: 1) control diet; 2) control diet + Rovabio; 3) 5% increase in amino acids; 4) 5% increase in amino acids + Rovabio; 5) 10% increase in amino acids; and 6) 10% increase in amino acids + Rovabio. +/ = Diets with or without Rovabio, respectively. 2 Represents eviscerated carcass without feet, shanks, and head but with neck. diet cost reductions are far greater than the current cost of ROV. In additional trials, control enzymes may be warranted to determine if en- zyme level or ratio is adequate to increase performance of broilers fed corn and soybean meal diets. Table 9. Processing traits of male broilers as affected by dietary amino acid density and Rovabio Excel feed enzyme fed from 1 to 49 d (experiment 3) 1 Abdominal fat Carcass 2 Breast meat 3 Weight Percentage Weight Percentage Weight Percentage Diet (kg) (% of BW) (kg) (% of BW) (kg) (% of BW) 33-d processing a a b SEM d processing a a a a b b SEM a,b Means with no common superscripts within a column differ (P < 0.05). 1 Three treatments were implemented in each experimental period: 1) control diet (100 ); 2) control diet + Rovabio (100+); and 3) 10% increase in amino acids (110). 2 Represents eviscerated carcass without feet, shanks, and head but with neck. 3 Represents pectoralis major and minor. CONCLUSIONS AND APPLICATIONS 1. Dietary ROV Excel and diet density (energy or amino acids) did not interact.

9 WEST ET AL.: DIET DENSITY AND ENZYME ADDITION Increasing amino acid density resulted in better feed conversion (2 of 3 experiments) and less relative abdominal fat (all 3 experiments). 3. Dietary addition of ROV Excel was without effect on growth, feed conversion, and carcass traits but reduced (P = 0.06) mortality in 2 experiments (d-14 mortality in experiment 1 and overall mortality in experiment 2). REFERENCES AND NOTES 1. Rovabio Excel; Adisseo, Alpharetta, GA. 2. Wu, Y. B., V. Ravindran, D. G. Thomas, M. J. Birtles, and W. H. Hendriks Influence of phytase and xylanase, individually or in combination, on performance, apparent metabolisable energy, digestive tract measurements and gut morphology in broilers fed wheat-based diets containing adequate level of phosphorus. Br. Poult. Sci. 45: Adisseo Rovabio Excel LC (Liquid) Quality Standard. Accessed Mar Cowieson, A. J., D. N. Singh, and O. Adeola Prediction of ingredient quality and the effect of a combination of xylanase, amylase, protease, and phytase in the diets of broiler chicks. 2. Energy and nutrient utilisation. Br. Poult. Sci. 47: Cowieson, A. J., and O. Adeola Carbohydrases, proteases, and phytase have an additive beneficial effect in nutritionally marginal diets for broiler chicks. Poult. Sci. 84: Vukic Vranjes, M., and C. Wenk Influence of dietary enzyme complex on the performance of broilers fed on diets with and without antibiotic supplementation. Br. Poult. Sci. 36: Pilgrim s Pride, Pittsburg, TX. 8. Aviagen, Albertville, AL. 9. SAS Institute Statistical Analytical System User s Guide. Version 6.12 ed. SAS Inst. Inc., Cary, NC. 10. Steel, R. G. D., and J. H. Torrie Principals and Procedures of Statistics. A Biometrical Approach. 2nd ed. McGraw-Hill, New York, NY. 11. Corzo, A., M. T. Kidd, D. J. Burnham, E. R. Miller, S. L. Branton, and R. Gonzalez-Esquerra Dietary amino acid density effects on growth and carcass characteristics of broilers differing in strain cross and sex. J. Appl. Poult. Res. 14: Kidd, M. T., C. D. McDaniel, S. L. Branton, E. R. Miller, B. B. Boren, and B. I. Fancher Increasing amino acid density improves live performance and carcass yields of commercial broilers. J. Appl. Poult. Res. 13: Engberg, R. M., M. S. Hedemann, S. Steenfeldt, and B. B. Jensen Influence of whole wheat and xylanase on broiler performance and microbial composition and activity in the digestive tract. Poult. Sci. 83: