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P. W. WALDROUP, J. A. ENGLAND, A. L. WALDROUP, and N. B. ANTHONY. Poultry Science Department, University of Arkansas, Fayetteville, Arkansas 72701.
Response of Two Strains of Large White Male Turkeys to Amino Acid Levels When Diets Are Changed at Three- or Four-Week Intervals1 P. W. WALDROUP, J. A. ENGLAND, A. L. WALDROUP, and N. B. ANTHONY Poultry Science Department, University of Arkansas, Fayetteville, Arkansas 72701 ABSTRACT A study was conducted to evaluate the amino acid recommendations of the NRC (1994) when diets were changed at 3- or 4-wk intervals. Diets formulated to provide from 90 to 115% of recommended amino acid levels were fed to Nicholas (NIC) and British United Turkey (BUT) Large White males from day-old to 24 wk of age; samples of turkeys were processed at 18 and 24 wk. Results indicated that the amino acid levels suggested by NRC are adequate to support maximum

body weight gain, feed conversion, and dressing percentage of Large White males grown to 18 or 24 wk when fed on 4-wk intervals. An approximately 5% higher level of amino acids was required to maximize breast yield. When feeds were changed at 3-wk intervals, higher levels of amino acids were required to maximize performance; however, there did not seem to be any difference in the response of the two strains of turkeys to different levels of amino acids in this study.

(Key words: turkey, amino acid, strain differences, requirements) 1997 Poultry Science 76:1543–1555

INTRODUCTION The NRC recently proposed new amino acid requirements for the turkey, as well as updated amino acid standards for feed ingredients (NRC, 1994). Studies in our laboratory (Adams et al., 1994; Waldroup et al. 1997) demonstrated that the Nicholas Large White male turkey had maximum weight gain and feed utilization when fed diets formulated to provide a minimum of 105% of NRC amino acid requirements. These diets were formulated to have as many of the essential amino acids as close to the minimum level as possible in order to critically evaluate the requirements. Differences in growth rate, carcass composition, and parts yield between and among strains of turkeys have been observed for many years (Asmundson and Lerner, 1940; Harshaw et al., 1943; Fry et al., 1962; Hartung and Froning, 1968; MacNeil and Buss, 1968; MacNeil, 1969; Hayse and Moreng, 1973; Orr et al., 1974; Clayton et al., 1978; Moran et al., 1978; Salmon et al., 1982a,b; Salmon, 1983; Larsen et al., 1986; Blair et al., 1989a,b; Lilburn and Nestor, 1991; Lilburn et al., 1992; Barbour and Lilburn, 1995). Because of noted differences in rate of gain at different stages of growth and in carcass conformation in modern commercial strains of Large White turkeys, some authors (Moran et al., 1984; Leeson and Caston, 1991; Lilburn, 1992) have suggested that the different strains may respond differently to nutrient levels or

Received for publication January 10, 1997. Accepted for publication June 22, 1997. 1Published with the approval of the Director, Arkansas Agricultural Experiment Station, Manuscript Number 96134.

feeding systems at some point in their growth cycle; however, others have failed to confirm this (Waibel et al., 1991; Lilburn and Emmerson, 1993). The objective of the present study was to further evaluate the NRC (1994) amino acid standards using two commercial strains of Large White male turkeys that differ significantly in their growth patterns, and to evaluate the effects on performance and carcass composition of the time at which diets are introduced.

MATERIALS AND METHODS

Dietary Treatments and Feeding Programs Six dietary treatments were compared, each fed at two different feed change intervals. The corn and soybean meal used in the study were analyzed for crude protein and moisture content prior to formulation and nutrient content adjusted accordingly. Diets were formulated to meet minimums of 90, 95, 100, 105, 110, and 115% of NRC (1994) suggested amino acid levels for the male turkey. The diets were formulated to have as many of the essential amino acids as close to the minimum level as possible by using commercially available amino acids (lysine, methionine, threonine, and tryptophan) and by manipulating the price of intact protein-containing ingredients (corn and soybean meal). Diets were maintained isocaloric by manipulation of levels of corn, soybean meal, and poultry oil; no attempts were made to maintain diets isonitrogenous. Diets were adequately supplemented with vitamins and trace minerals using commercial

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WALDROUP ET AL. TABLE 1. Composition and calculated nutrient content of diets formulated to contain different levels of amino acids and fed from 0 to 3 wk (3-wk interval feeding) or 0 to 4 wk (4-wk interval feeding) Percentage of NRC recommendations

Ingredient

90%

95%

100%

105%

110%

115%

Yellow corn Soybean meal (48% CP) Poultry oil Dicalcium phosphate Limestone Lysine HCl (98%) DL Methionine (98%) Threonine Vitamin premix1 Trace minerals2 Salt BMD 503 Amprol 25%4

523.53 423.92 0.00 25.12 14.12 0.62 1.69 0.00 5.00 1.00 4.00 0.50 0.50 1,000.00

521.47 424.39 0.00 25.13 14.11 1.63 2.22 0.05 5.00 1.00 4.00 0.50 0.50 1,000.00

488.45 452.35 4.91 24.94 14.04 1.71 2.48 0.12 5.00 1.00 4.00 0.50 0.50 1,000.00

448.49 486.58 10.94 24.70 13.95 1.57 2.67 0.10 5.00 1.00 4.00 0.50 0.50 1,000.00

408.54 520.80 16.97 24.47 13.85 1.43 2.87 0.07 5.00 1.00 4.00 0.50 0.50 1,000.00

368.58 555.03 23.00 24.23 13.76 1.29 3.06 0.05 5.00 1.00 4.00 0.50 0.50 1,000.00

2,800 24.75 1.67 0.66 1.05 2.11 1.44 0.55 1.19 0.94 0.35 1.15 2.28 0.95 2.18

2,800 24.89 1.68 0.66 1.05 2.11 1.52 0.60 1.19 0.95 0.35 1.15 2.28 1.00 2.18

2,800 25.96 1.76 0.69 1.10 2.18 1.60 0.64 1.24 1.00 0.36 1.20 2.38 1.05 2.27

2,800 27.24 1.86 0.73 1.16 2.27 1.68 0.67 1.31 1.05 0.39 1.26 2.51 1.10 2.39

2,800 28.53 1.97 0.76 1.22 2.36 1.76 0.71 1.37 1.10 0.41 1.32 2.64 1.16 2.51

2,800 29.81 2.07 0.80 1.28 2.45 1.84 0.74 1.44 1.15 0.43 1.38 2.76 1.21 2.63

(g/kg)

Calculated analysis5 AMEn, kcal/kg CP, % Arg, % His, % Ile, % Leu, % Lys, % Met, % Phe, % Thr, % Trp, % Val, % Gly+Ser, % TSAA, % Phe+Tyr, %

1Provides per kilogram of diet: vitamin A (from vitamin A acetate), 16,520 IU; cholecalciferol, 7,158 IU; vitamin E (from dl-a tocopheryl acetate), 50 IU; vitamin B12, 0.022 mg; menadione (from menadione sodium bisulfite complex), 3.85 mg; riboflavin, 13.75 mg; pantothenic acid (from dl-calcium pantothenate), 30.25 mg; thiamin (from thiamin mononitrate), 3.3 mg; niacin, 105 mg; pyridoxine (from pyridoxine HCl), 5.5 mg; folacin, 2.2 mg; biotin, 0.181 mg; ethoxyquin, 125 mg; Se, 0.275 mg. 2Provides per kilogram of diet: Mn (from MnSO ·H O), 100 mg; Zn (from ZnSO ·7H O), 100 mg; Fe (from FeSO ·7H O), 50 mg; Cu (from 4 2 4 2 4 2 CuSO4·5H2O), 10 mg; I [from Ca(IO3)2·H2O], 1 mg. 3A. L. Pharma, Inc., Ft. Lee, NJ 07024. 4Merck AgVet Division, Merck and Co., Inc., Rahway, NJ 07065. 5Values in bold face are at minimum specified level.

premixes obtained from a local turkey integrator. Composition of the diets and calculated nutrient content are given in Tables 1 to 6. Calculated nutrient analysis of the diets indicated that lysine and methionine or TSAA were at minimum levels in all diets. Threonine was at minimum levels in all but one of the diets, and valine and isoleucine were frequently at their minimum requirements. Virtually all studies concerning amino acid requirements of turkeys focus primarily upon lysine or methionine requirements, and seldom are other amino acids considered to be limiting factors. Samples of all diets were assayed for crude protein content to verify proper mixing; samples of diets with 90, 100, and 110% of suggested amino acid levels were assayed for total and supplemental amino acid content by

2Degussa Corp., Allendale, NJ 07401. 3Goldsboro Milling Co., Goldsboro, NC

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a commercial laboratory.2 Crude protein and amino acid analyses were in close agreement with calculated values (data not shown for brevity). The diets were changed at two different age intervals; one group was changed at 4-wk intervals as suggested by NRC, whereas the second group was changed at 3-wk intervals, as is often done in commercial practice (NRC, 1994) and in several research studies evaluating NRC recommendations (Moran et al., 1995; Waibel et al., 1995). Diets within an age period were isocaloric and fed in pellet form with crumbles used for starter diets (0 to 3 or 0 to 4 wk).

Birds and Housing Day-old male Large White turkey poults were obtained from a commercial hatchery3 on April 20 and fed to October 5 for a 24-wk growing period. Twelve Nicholas

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AMINO ACID REQUIREMENTS OF TURKEYS TABLE 2. Composition and calculated nutrient content of diets formulated to contain different levels of amino acids and fed from 3 to 6 wk (3-wk interval feeding) or 4 to 8 wk (4-wk interval feeding) Percentage of NRC recommendations Ingredients and analysis

90%

95%

100%

105%

110%

115%

(g/kg) Yellow corn Soybean meal (48% CP) Poultry oil Dicalcium phosphate Limestone Lysine HCl (98%) DL Methionine (98%) Threonine Vitamin premix1 Trace minerals2 Salt BMD 503 Amprol 25%4 Calculated analysis5 AMEn, kcal/kg CP, % Arg, % His, % Ile, % Leu, % Lys, % Met, % Phe, % Thr, % Trp, % Val, % Gly+Ser, % TSAA, % Phe+Tyr, %

611.25 340.78 0.22 20.33 12.07 2.32 1.63 0.40 5.00 1.00 4.00 0.50 0.50 1,000.00

578.20 368.88 5.17 20.14 12.00 2.33 1.83 0.45 5.00es 1.00 4.00 0.50 0.50 1,000.00

545.04 397.11 10.13 19.94 11.92 2.33 2.04 0.49 5.00 1.00 4.00 0.50 0.50 1,000.00

508.36 428.49 15.66 19.73 11.84 2.22 2.21 0.49 5.00 1.00 4.00 0.50 0.50 1,000.00

471.68 459.88 21.19 19.51 11.76 2.12 2.38 0.48 5.00 1.00 4.00 0.50 0.50 1,000.00

435.03 491.26 26.71 19.30 11.67 2.01 2.55 0.47 5.00 1.00 4.00 0.50 0.50 1,000.00

2,900 21.73 1.42 0.58 0.90 1.89 1.35 0.50 1.03 0.86 0.29 1.00 1.97 0.86 1.88

2,900 22.80 1.50 0.61 0.95 1.96 1.43 0.53 1.08 0.90 0.31 1.05 2.07 0.90 1.98

2,900 23.88 1.59 0.63 1.00 2.03 1.50 0.57 1.14 0.95 0.33 1.10 2.17 0.95 2.07

2,900 25.06 1.68 0.67 1.06 2.11 1.58 0.60 1.20 1.00 0.35 1.16 2.29 1.00 2.18

2,900 26.24 1.78 0.70 1.11 2.19 1.65 0.63 1.26 1.05 0.37 1.21 2.40 1.05 2.29

2,900 27.41 1.88 0.73 1.17 2.27 1.73 0.66 1.32 1.09 0.39 1.27 2.52 1.09 2.40

1Provides per kilogram of diet: vitamin A (from vitamin A acetate), 16,520 IU; cholecalciferol, 7,158 IU; vitamin E (from dl-a tocopheryl acetate), 50 IU; vitamin B12, 0.022 mg; menadione (from menadione sodium bisulfite complex), 3.85 mg; riboflavin, 13.75 mg; pantothenic acid (from dl-calcium pantothenate), 30.25 mg; thiamin (from thiamin mononitrate), 3.3 mg; niacin, 105 mg; pyridoxine (from pyridoxine HCl), 5.5 mg; folacin, 2.2 mg; biotin, 0.181 mg; ethoxyquin, 125 mg; Se, 0.275 mg. 2Provides per kilogram of diet: Mn (from MnSO ·H O), 100 mg; Zn (from ZnSO ·7H O), 100 mg; Fe (from FeSO ·7H O), 50 mg; Cu (from 4 2 4 2 4 2 CuSO4·5H2O), 10 mg; I [from Ca(IO3)2·H2O], 1 mg. 3A. L. Pharma, Inc., Ft. Lee, NJ 07024. 4Merck AgVet Division, Merck and Co., Inc., Rahway, NJ 07065. 5Values in bold face are at minimum specified level.

884 (NIC) strain poults were placed in each of 48 pens, and 12 British United Turkeys Big 65 (BUT) strain poults were placed in each of an additional 48 pens for a total of 576 poults of each strain. Pens with NIC poults alternated with pens with BUT poults in the house. New softwood shavings were used over concrete floors. The pens were 5.2 m2 and equipped with a hanging automatic water fount and two tube feeders, replaced at 9 wk by a small range-type feeder. Supplemental feeder flats and water founts were used during the 1st wk. Temperature and ventilation were adjusted by thermostatically controlled brooder stoves, fans, and sidewall curtains. Daily records of high and low temperatures were taken throughout the study; high ambient temperatures were encountered from 10 to 20 wk of age (Figure 1).

4Nicholas Turkey Breeding Farms, Sonoma, CA 5British United Turkeys, Lewisburg, WV 24901.

95476.

Measurements Feed consumption was determined at each feed change interval. Turkeys were individually weighed at 6, 12, 18, and 24 wk of age. Any bird that died or was removed for cannibalism or obvious leg disorders was weighed and the weight used to adjust feed consumption. Samples of birds (two per pen nearest the pen mean weight) were processed at 18 and 24 wk of age to determine dressing percentage and abdominal fat content. Deboned breast meat yield and percentage of leg quarter, wing, and skeletal rack were determined on chilled carcasses. Processing techniques were described by Waldroup et al. (1997).

Statistical Analysis Pen means served as the experimental unit. Data were subjected to analysis of variance using the General Linear Models procedure of SAS Institute (1982). The model

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WALDROUP ET AL. TABLE 3. Composition and calculated nutrient content of diets formulated to contain different levels of amino acids and fed from 6 to 9 wk (3-wk interval feeding) or 8 to 12 wk (4-wk interval feeding) Percentage of NRC recommendations

Ingredients and analyses

90%

95%

100%

105%

110%

115%

Yellow corn Soybean meal (48% CP) Poultry oil Dicalcium phosphate Limestone Lysine HCl (98%) DL Methionine (98%) Threonine Vitamin premix1 Trace minerals2 Salt BMD 503

709.64 247.98 0.00 16.69 10.77 3.21 1.21 0.50 5.00 1.00 4.00 0.50 1,000.00

690.19 264.08 2.82 16.58 10.72 3.49 1.46 0.66 5.00 1.00 4.00 0.50 1,000.00

663.65 286.58 6.77 16.42 10.66 3.56 1.64 0.72 5.00 1.00 4.00 0.50 1,000.00

634.59 311.33 11.13 16.26 10.59 3.55 1.81 0.74 5.00 1.00 4.00 0.50 1,000.00

604.50 337.03 15.65 16.08 10.53 3.51 1.96 0.74 5.00 1.00 4.00 0.50 1,000.00

574.41 362.72 20.17 15.91 10.46 3.47 2.11 0.75 5.00 1.00 4.00 0.50 1,000.00

3,000 18.22 1.13 0.48 0.63 1.64 1.17 0.41 0.85 0.72 0.23 0.83 1.62 0.72 1.55

3,000 18.87 1.18 0.50 0.76 1.68 1.24 0.45 0.88 0.76 0.24 0.86 1.67 0.76 1.60

3,000 19.74 1.25 0.52 0.80 1.74 1.30 0.47 0.92 0.80 0.25 0.90 1.76 0.80 1.68

3,000 20.68 1.33 0.54 0.84 1.80 1.37 0.50 0.97 0.84 0.27 0.95 1.85 0.84 1.77

3,000 21.65 1.40 0.57 0.89 1.87 1.43 0.53 1.02 0.88 0.29 0.99 1.94 0.88 1.86

3,000 22.62 1.48 0.60 0.94 1.93 1.50 0.56 1.07 0.92 0.30 1.04 2.04 0.92 1.95

(g/kg)

Calculated analysis4 AMEn, kcal/kg CP, % Arg, % His, % Ile, % Leu, % Lys, % Met, % Phe, % Thr, % Trp, % Val, % Gly+Ser, % TSAA, % Phe+Tyr, %

1Provides per kilogram of diet: vitamin A (from vitamin A acetate), 16,520 IU; cholecalciferol, 7,158 IU; vitamin E (from dl-a tocopheryl acetate), 50 IU; vitamin B12, 0.022 mg; menadione (from menadione sodium bisulfite complex), 3.85 mg; riboflavin, 13.75 mg; pantothenic acid (from dl-calcium pantothenate), 30.25 mg; thiamin (from thiamin mononitrate), 3.3 mg; niacin, 105 mg; pyridoxine (from pyridoxine HCl), 5.5 mg; folacin, 2.2 mg; biotin, 0.181 mg; ethoxyquin, 125 mg; Se, 0.275 mg. 2Provides per kilogram of diet: Mn (from MnSO ·H O), 100 mg; Zn (from ZnSO ·7H O), 100 mg; Fe (from FeSO ·7H O), 50 mg; Cu (from 4 2 4 2 4 2 CuSO4·5H2O), 10 mg; I [from Ca(IO3)2·H2O], 1 mg. 3A. L. Pharma, Inc., Ft. Lee, NJ 07024. 4Values in bold face are at minimum specified level.

included main effects of amino acid level, strain, feed change interval, and all possible interactions. Where significant differences (P ≤ 0.05) were observed among or between treatment means, mean separation was accomplished by repeated t tests using the least squares means (lsmeans) option of the General Linear Models procedure (GLM).

RESULTS

Body Weight

FIGURE 1. Mean weekly temperature during the study.

Probabilities and mean standard errors of the main effects of amino acid level, feed change interval, strain, and all possible interactions on body weight are shown in Table 7. Body weight was significantly influenced by dietary amino acid level and feed change interval at 6, 12, 18, and 24 wk with a significant interaction of dietary amino acid level and feed change interval at 12, 18, and 24 wk (Table 8). At 6 wk, poults required greater than 105%

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AMINO ACID REQUIREMENTS OF TURKEYS TABLE 4. Composition and calculated nutrient content of diets formulated to contain different levels of amino acids and fed from 9 to 12 wk (3-wk interval feeding) or 12 to 16 wk (4-wk interval feeding) Percentage of NRC recommendations Ingredients and analysis

90%

95%

100%

105%

110%

115%

Yellow corn Soybean meal (48% CP) Poultry oil Dicalcium phosphate Limestone Lysine HCl (98%) DL Methionine (98%) Threonine Vitamin premix1 Trace minerals2 Salt BMD 503

769.49 185.68 6.84 15.00 9.49 1.92 0.53 1.05 5.00 1.00 4.00 0.50 1,000.00

742.91 208.48 10.87 14.85 9.43 1.78 0.61 1.07 5.00 1.00 4.00 0.50 1,000.00

716.29 231.30 14.89 14.69 9.37 1.65 0.71 1.10 5.00 1.00 4.00 0.50 1,000.00

689.68 254.11 18.91 14.54 9.31 1.51 0.82 1.12 5.00 1.00 4.00 0.50 1,000.00

663.05 276.93 22.94 14.38 9.25 1.38 0.92 1.15 5.00 1.00 4.00 0.50 1,000.00

636.45 299.74 26.96 14.22 9.19 1.24 1.03 1.17 5.00 1.00 4.00 0.50 1,000.00

3,100 15.65 0.94 0.41 0.62 1.46 0.90 0.32 0.73 0.68 0.18 0.72 1.38 0.59 1.32

3,100 16.50 1.01 0.44 0.66 1.52 0.95 0.33 0.77 0.71 0.20 0.76 1.46 0.62 1.40

3,100 17.35 1.08 0.46 0.70 1.58 1.00 0.35 0.81 0.75 0.21 0.80 1.54 0.65 1.48

3,100 18.21 1.15 0.48 0.74 1.64 1.05 0.38 0.86 0.79 0.23 0.84 1.63 0.68 1.56

3,100 19.06 1.22 0.51 0.78 1.70 1.10 0.40 0.90 0.83 0.24 0.88 1.71 0.72 1.64

3,100 19.91 1.28 0.53 0.82 1.76 1.15 0.42 0.94 0.86 0.26 0.92 1.80 0.75 1.72

(g/kg)

Calculated analysis4 AMEn, kcal/kg CP, % Arg, % His, % Ile, % Leu, % Lys, % Met, % Phe, % Thr, % Trp, % Val, % Gly+Ser, % TSAA, % Phe+Tyr, %

1Provides per kilogram of diet: vitamin A (from vitamin A acetate), 16,520 IU; cholecalciferol, 7,158 IU; vitamin E (from dl-a tocopheryl acetate), 50 IU; vitamin B12, 0.022 mg; menadione (from menadione sodium bisulfite complex), 3.85 mg; riboflavin, 13.75 mg; pantothenic acid (from dl-calcium pantothenate), 30.25 mg; thiamin (from thiamin mononitrate), 3.3 mg; niacin, 105 mg; pyridoxine (from pyridoxine HCl), 5.5 mg; folacin, 2.2 mg; biotin, 0.181 mg; ethoxyquin, 125 mg; Se, 0.275 mg. 2Provides per kilogram of diet: Mn (from MnSO ·H O), 100 mg; Zn (from ZnSO ·7H O), 100 mg; Fe (from FeSO ·7H O), 50 mg; Cu (from 4 2 4 2 4 2 CuSO4·5H2O), 10 mg; I [from Ca(IO3)2·H2O], 1 mg. 3A. L. Pharma, Inc., Ft. Lee, NJ 07024. 4Values in bold face are at minimum specified level.

of NRC (1994) recommended amino acid levels to maximize body weight irrespective of feed change interval. At 12 wk, poults fed diets changed at 3-wk intervals required more than 105% of the recommended amino acid levels to maximize body weight; however, this was less than the maximum weight attained by poults fed diets changed at 4-wk intervals. Poults fed diets changed at 4-wk intervals required more than 100% of the recommended amino acid levels to maximize body weight. At 18 wk, poults fed diets changed at 3-wk intervals required more than 110% of the recommended amino acid levels to maximize body weight, whereas poults fed diets changed at 4-wk intervals maximized body weight at 100% of the recommended amino acid levels. At 24 wk, poults fed diets changed at 3-wk intervals required greater than 100% of the recommended amino acid levels to maximize body weight but poults fed diets changed at 4-wk intervals required no more than 95% of the recommended amino acid levels to maximize body weight.

The NIC turkeys were significantly heavier than BUT turkeys at 6 and 12 wk with no significant difference between the strains at 18 wk. At 24 wk, BUT turkeys were significantly heavier than NIC turkeys. There were no significant interactions of strain of bird and amino acid level, strain of bird and feed change interval (data not shown), or strain of bird, amino acid level, and feed change interval (data not shown) on body weight.

Feed Conversion Probabilities and mean standard errors of the main effects of amino acid level, feed change interval, strain, and all possible interactions on feed conversion are shown in Table 7. Dietary amino acid levels significantly influenced feed conversion at 6, 12, and 18 wk but had no significant effect at 24 wk (Table 9). Feed conversion was generally maximized at 100 to 105% of the recommended amino acid levels. Feed change interval significantly influenced feed conversion at 12 and 18 wk

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WALDROUP ET AL. TABLE 5. Composition and calculated nutrient content of diets formulated to contain different levels of amino acids and fed from 12 to 15 wk (3-wk interval feeding) or 16 to 20 wk (4-wk interval feeding) Percentage of NRC recommendations

Ingredients and analysis

90%

95%

100%

105%

110%

115%

Yellow corn Soybean meal (48% CP) Poultry oil Dicalcium phosphate Limestone Lysine HCl (98%) DL Methionine (98%) Threonine Vitamin premix1 Trace minerals2 Salt BMD 503

814.49 137.03 15.66 12.15 8.77 1.31 0.11 0.48 5.00 1.00 4.00 0.50 1,000.00

791.31 156.97 19.18 12.01 8.72 1.14 0.20 0.47 5.00 1.00 4.00 0.50 1,000.00

768.14 176.91 22.70 11.87 8.66 0.98 0.28 0.46 5.00 1.00 4.00 0.50 1,000.00

744.95 196.86 26.22 11.73 8.61 0.81 0.36 0.46 5.00 1.00 4.00 0.50 1,000.00

721.76 216.80 29.74 11.60 8.56 0.65 0.44 0.45 5.00 1.00 4.00 0.50 1,000.00

698.58 236.74 33.26 11.46 8.51 0.48 0.52 0.45 5.00 1.00 4.00 0.50 1,000.00

3,200 13.60 0.79 0.36 0.53 1.33 0.72 0.25 0.63 0.54 0.15 0.63 1.19 0.50 1.14

3,200 14.34 0.85 0.38 0.56 1.38 0.76 0.27 0.67 0.57 0.16 0.67 1.26 0.52 1.21

3,200 15.07 0.91 0.40 0.60 1.43 0.80 0.28 0.71 0.60 0.18 0.70 1.34 0.55 1.28

3,200 15.81 0.97 0.42 0.63 1.48 0.84 0.30 0.74 0.63 0.19 0.74 1.41 0.58 1.35

3,200 16.55 1.03 0.44 0.67 1.53 0.88 0.32 0.78 0.66 0.20 0.77 1.48 0.61 1.42

3,200 17.29 1.09 0.46 0.70 1.58 0.92 0.34 0.82 0.69 0.22 0.81 1.56 0.63 1.49

(g/kg)

Calculated analysis4 AMEn, kcal/kg CP, % Arg, % His, % Ile, % Leu, % Lys, % Met, % Phe, % Thr, % Trp, % Val, % Gly+Ser, % TSAA, % Phe+Tyr, %

1Provides per kilogram of diet: vitamin A (from vitamin A acetate), 16,520 IU; cholecalciferol, 7,158 IU; vitamin E (from dl-a tocopheryl acetate), 50 IU; vitamin B12, 0.022 mg; menadione (from menadione sodium bisulfite complex), 3.85 mg; riboflavin, 13.75 mg; pantothenic acid (from dl-calcium pantothenate), 30.25 mg; thiamin (from thiamin mononitrate), 3.3 mg; niacin, 105 mg; pyridoxine (from pyridoxine HCl), 5.5 mg; folacin, 2.2 mg; biotin, 0.181 mg; ethoxyquin, 125 mg; Se, 0.275 mg. 2Provides per kilogram of diet: Mn (from MnSO ·H O), 100 mg; Zn (from ZnSO ·7H O), 100 mg; Fe (from FeSO ·7H O), 50 mg; Cu (from 4 2 4 2 4 2 CuSO4·5H2O), 10 mg; I [from Ca(IO3)2·H2O], 1 mg. 3A. L. Pharma, Inc., Ft. Lee, NJ 07024. 4Values in bold face are at minimum specified level.

but not at 6 or 24 wk. Poults fed diets changed at 4-wk intervals had significantly better feed conversion at 12 and 18 wk than those fed diets changed at 3-wk intervals. There were no interactions of dietary amino acid level and feed change interval on feed conversion at any age examined. No significant differences in feed conversion were observed between strains at 6, 12, or 18 wk. At 24 wk, feed conversion by NIC turkeys was significantly better than that of BUT turkeys.

Carcass Characteristics Probabilities and mean standard errors of the main effects of amino acid level, feed change interval, strain, and all possible interactions on dressing percentage, abdominal fat, breast yield, leg quarter yield, wing yield, and skeletal rack yield at 18 or 24 wk are shown in Table 10. Dressing percentage was not significantly influenced by amino acid level, feed change interval, strain of bird, or any interaction among these factors (Table 11). Abdominal

fat content was not significantly affected by amino acid level at 18 wk but significantly reduced by increasing amino acid levels at 24 wk (Table 11). Birds fed diets changed at 4-wk intervals had significantly less abdominal fat at 18 wk and numerically less fat at 24 wk than birds fed diets changed at 3-wk intervals. There were no significant interactions of strain of bird and amino acid level, strain of bird and feed change interval (data not shown), or strain of bird, amino acid level, and feed change interval (data not shown) on abdominal fat content. Breast meat yield was significantly affected by amino acid level at 18 and 24 wk (Table 12). At both ages, breast meat yield increased as dietary amino acid content increased from 90 to 115% of recommended levels. At 18 wk, feeding 100% of recommended levels resulted in a breast yield that was not statistically exceeded by higher levels; at 24 wk feeding 105% of recommended levels gave maximum breast yield. The NIC birds had significantly higher breast yield than BUT birds at 18 wk but there was no difference in breast yield between the strains at 24 wk.

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AMINO ACID REQUIREMENTS OF TURKEYS TABLE 6. Composition and calculated nutrient content of diets formulated to contain different levels of amino acids and fed from 15 to 24 wk (3-wk interval feeding) or 20 to 24 wk (4-wk interval feeding) Percentage of NRC recommendations Ingredients and analysis

90%

95%

100%

105%

110%

115%

Yellow corn Soybean meal (48% CP) Poultry oil Dicalcium phosphate Limestone Lysine HCl (98%) DL Methionine (98%) Threonine Vitamin premix1 Trace minerals2 Salt BMD 503

856.70 88.88 24.86 10.37 7.46 1.27 0.11 0.35 5.00 1.00 4.00 0.50 1,000.00

836.88 105.97 27.88 10.26 7.41 1.10 0.16 0.34 5.00 1.00 4.00 0.50 1,000.00

817.07 123.05 30.90 10.14 7.36 0.94 0.21 0.33 5.00 1.00 4.00 0.50 1,000.00

797.28 140.13 33.91 10.02 7.32 0.77 0.25 0.32 5.00 1.00 4.00 0.50 1,000.00

777.47 157.21 36.93 9.90 7.27 0.61 0.30 0.31 5.00 1.00 4.00 0.50 1,000.00

757.65 174.30 39.95 9.79 7.23 0.44 0.35 0.29 5.00 1.00 4.00 0.50 1,000.00

3,300 11.66 0.63 0.31 0.44 1.19 0.59 0.23 0.53 0.45 0.12 0.54 1.00 0.44 0.96

3,300 12.28 0.69 0.33 0.47 1.23 0.62 0.24 0.57 0.48 0.13 0.57 1.06 0.46 1.02

3,300 12.91 0.74 0.35 0.50 1.28 0.65 0.25 0.60 0.50 0.14 0.60 1.13 0.49 1.08

3,300 13.54 0.79 0.36 0.53 1.32 0.68 0.26 0.63 0.53 0.15 0.63 1.19 0.51 1.14

3,300 14.17 0.84 0.38 0.56 1.37 0.72 0.28 0.66 0.55 0.16 0.66 1.25 0.53 1.20

3,300 14.80 0.89 0.40 0.59 1.41 0.75 0.29 0.70 0.58 0.17 0.69 1.32 0.55 1.26

(g/kg)

Calculated analysis4 AMEn, kcal/kg CP, % Arg, % His, % Ile, % Leu, % Lys, % Met, % Phe, % Thr, % Trp, % Val, % Gly+Ser, % TSAA, % Phe+Tyr, %

1Provides per kilogram of diet: vitamin A (from vitamin A acetate), 16,520 IU; cholecalciferol, 7,158 IU; vitamin E (from dl-a tocopheryl acetate), 50 IU; vitamin B12, 0.022 mg; menadione (from menadione sodium bisulfite complex), 3.85 mg; riboflavin, 13.75 mg; pantothenic acid (from dl-calcium pantothenate), 30.25 mg; thiamin (from thiamin mononitrate), 3.3 mg; niacin, 105 mg; pyridoxine (from pyridoxine HCl), 5.5 mg; folacin, 2.2 mg; biotin, 0.181 mg; ethoxyquin, 125 mg; Se, 0.275 mg. 2Provides per kilogram of diet: Mn (from MnSO ·H O), 100 mg; Zn (from ZnSO ·7H O), 100 mg; Fe (from FeSO ·7H O), 50 mg; Cu (from 4 2 4 2 4 2 CuSO4·5H2O), 10 mg; I [from Ca(IO3)2·H2O], 1 mg. 3A. L. Pharma, Inc., Ft. Lee, NJ 07024. 4Values in bold face are at minimum specified level.

TABLE 7. Probabilities and mean standard errors of the effects of amino acid levels, feed change interval, strain, and their interactions on body weight and feed conversion of male Large White turkeys 6 wk Variable Body weight Amino acid (AA) Interval (INT) Strain (STR) AA × INT AA × STR INT × STR AA × INT × STR Feed conversion Amino acid (AA) Interval (INT) Strain (STR) AA × INT AA × STR INT × STR AA × INT × STR

12 wk

18 wk

24 wk

P > F

SEM

P > F

SEM

P > F

SEM

P > F

SEM

0.0001 0.0017 0.0001 0.12 0.43 0.28 0.79

0.022 0.0129 0.0129 0.031 0.031 0.018 0.044

0.0001 0.0001 0.005 0.009 0.77 0.95 0.56

0.072 0.041 0.041 0.102 0.102 0.058 0.144

0.0001 0.0001 0.30 0.03 0.68 0.61 0.52

0.139 0.08 0.08 0.197 0.197 0.113 0.278

0.0002 0.02 0.06 0.03 0.12 0.70 0.90

0.200 0.115 0.115 0.284 0.284 0.164 0.401

0.0001 0.29 0.40 0.26 0.11 0.91 0.53

0.015 0.008 0.008 0.021 0.021 0.012 0.031

0.01 0.0001 0.08 0.93 0.07 0.96 0.74

0.026 0.015 0.015 0.037 0.037 0.021 0.053

0.04 0.03 0.32 0.34 0.68 0.66 0.94

0.051 0.029 0.029 0.072 0.072 0.042 0.103

0.24 0.20 0.03 0.46 0.30 0.93 0.94

0.053 0.031 0.031 0.075 0.075 0.043 0.106

1550

WALDROUP ET AL. TABLE 8. Effect of dietary amino acid level and time of changing diets on body weight of two strains of male Large White turkeys

Variable

Change interval

6-wk weight, kg BUT Nicholas 3 wk 4 wk Mean 12-wk weight, kg BUT Nicholas 3 4 Mean 18-wk weight, kg BUT Nicholas 3 4 Mean 24-wk weight, kg BUT Nicholas 3 4 Mean

wk wk

wk wk

wk wk

Percentage of NRC recommendations 90%

95%

100%

105%

110%

115%

Mean

2.061 2.186 2.145 2.103 2.124e

2.201 2.281 2.212 2.270 2.241d

2.270 2.365 2.300 2.335 2.317c

2.349 2.472 2.373 2.449 2.411b

2.484 2.488 2.419 2.554 2.486a

2.409 2.494 2.405 2.498 2.451ab

2.296y 2.381x 2.309s 2.368r

6.728 7.031 6.503e 7.256cd 6.879

7.460 7.617 7.159cd 7.919b 7.539

7.597 7.795 7.415c 7.978b 7.696

7.603 7.851 7.106d 8.348a 7.726

8.010 8.028 7.717b 8.321a 8.019

8.172 8.277 7.961b 8.488a 8.225

7.598y 7.766x 7.310 8.054

10.530 10.909 10.024f 11.416d 10.720

11.390 11.425 10.844e 11.970bc 11.407

11.750 12.137 11.477cd 12.340ab 11.938

12.106 12.192 11.733c 12.565a 12.149

12.175 12.169 11.706cd 12.638a 12.172

12.599 12.427 12.486ab 12.540a 12.513

11.758 11.874 11.378 12.254

15.794 16.435 15.481d 16.748c 16.114

17.025 16.978 16.860bc 17.143abc 17.001

17.483 16.826 17.038bc 17.271abc 17.154

17.556 17.206 17.220abc 17.541ab 17.381

17.716 17.114 17.015bc 17.816a 17.415

17.659 16.823 17.584ab 16.897bc 17.241

17.205x 16.897y 16.866 17.236

a–eSignificant

difference among amino acid levels (P < 0.05). difference between feed change intervals (P < 0.05). x,ySignificant difference between strains of turkeys (P < 0.05). r,sSignificant

TABLE 9. Effect of dietary amino acid level and time of changing diets on feed conversion by two strains of male Large White turkeys

Variable

Change interval

0 to 6 wk feed:gain, g:g BUT Nicholas 3 wk 4 wk Mean 0 to 12 wk feed:gain, g:g BUT Nicholas 3 wk 4 wk Mean 0 to 18 wk feed:gain, g:g BUT Nicholas 3 wk 4 wk Mean 0 to 24 wk feed:gain, g:g BUT Nicholas 3 wk 4 wk Mean a–cSignificant

Percentage of NRC recommendations 90%

95%

100%

105%

110%

115%

Mean

1.665 1.583 1.600 1.648 1.624a

1.566 1.570 1.581 1.556 1.568b

1.542 1.513 1.523 1.532 1.528bc

1.520 1.523 1.544 1.499 1.521c

1.479 1.521 1.519 1.481 1.500c

1.502 1.501 1.516 1.488 1.502c

1.546 1.535 1.547 1.534

1.923 1.851 1.931 1.843 1.887a

1.828 1.828 1.896 1.760 1.828ab

1.762 1.819 1.856 1.725 1.791b

1.809 1.819 1.892 1.735 1.814ab

1.739 1.891 1.873 1.757 1.815ab

1.705 1.792 1.793 1.703 1.748b

1.794 1.833 1.874r 1.754s

2.503 2.424 2.517 2.410 2.463a

2.469 2.390 2.562 2.297 2.429ab

2.370 2.222 2.321 2.269 2.295bc

2.307 2.297 2.352 2.252 2.302bc

2.277 2.365 2.379 2.263 2.321abc

2.278 2.257 2.228 2.307 2.267c

2.367 2.325 2.393r 2.299s

2.695 2.505 2.614 2.586 2.600

2.685 2.523 2.695 2.513 2.604

2.560 2.332 2.423 2.469 2.446

2.490 2.505 2.581 2.414 2.497

2.494 2.561 2.558 2.497 2.527

2.541 2.457 2.470 2.527 2.499

2.577x 2.480y 2.556 2.499

difference among amino acid levels (P < 0.05). difference between feed change intervals (P < 0.05). x,ySignificant difference between strains of turkeys (P < 0.05). r,sSignificant

1551

AMINO ACID REQUIREMENTS OF TURKEYS TABLE 10. Probabilities and mean standard errors of the effects of amino acid levels, feed change interval, strain, and their interactions on processing characteristics of male Large White turkeys 18 wk Variable Dressing percentage, % Amino acid (AA) Interval (INT) Strain (STR) AA × INT AA × STR INT × STR AA × INT × STR Abdominal fat, % AA INT STR AA × INT AA × STR INT × STR AA × INT × STR Breast yield, % AA INT STR AA × INT AA × STR INT × STR AA × INT × STR Leg quarter yield, % AA INT STR AA × INT AA × STR INT × STR AA × INT × STR Wing yield, % AA INT STR AA × INT AA × STR INT × STR AA × INT × STR Rack yield, % AA INT STR AA × INT AA × STR INT × STR AA × INT × STR

Birds whose diets were changed at 4-wk intervals (in effect resulting in greater overall amino acid intake) had significantly greater breast yield than birds whose diets were changed at 3-wk intervals. There were no significant interactions of amino acid level and feed change interval, strain of bird and amino acid level, strain of bird and feed change interval (data not shown), or strain of bird, amino acid level, and feed change interval (data not shown) on breast meat yield. Leg quarter yield was typically inversely related to breast meat yield (Table 12). Leg quarter yield was significantly higher at 18 wk for BUT poults than for NIC poults. Birds whose diets were changed at 3-wk intervals

24 wk

P > F

SEM

P > F

SEM

0.8398 0.0697 0.7368 0.8384 0.4955 0.2056 0.8299

0.5410 0.7360 0.3150 0.7950 0.7350 0.4480 0.6040

0.4076 0.1249 0.3538 0.1743 0.0967 0.9037 0.2848

0.4054 0.2373 0.2366 0.5733 0.5733 0.3324 0.8109

0.3862 0.0034 0.2804 0.8482 0.2793 0.4853 0.4866

0.1120 0.0650 0.0650 0.1647 0.1620 0.0938 0.2157

0.0044 0.2895 0.0165 0.9283 0.3696 0.7599 0.3611

0.1044 0.0505 0.0603 0.1477 0.1477 0.0856 0.2088

0.0379 0.0001 0.0001 0.1222 0.4866 0.6371 0.4024

0.4030 0.2330 0.2380 0.5590 0.5720 0.3407 0.7890

0.0008 0.0006 0.8773 0.0666 0.0606 0.9817 0.4360

0.4808 0.2779 0.2782 0.6800 0.6800 0.3911 0.9617

0.4023 0.0063 0.0001 0.7490 0.2745 0.9936 0.0044

0.3990 0.2260 0.2280 0.5770 0.5830 0.3360 0.7550

0.0008 0.0050 0.1000 0.6444 0.1986 0.9092 0.7833

0.4153 0.2412 0.2406 0.5873 0.5873 0.3407 0.8306

0.4636 0.8008 0.0507 0.2464 0.3328 0.4187 0.1426

0.2233 0.1250 0.1250 0.2930 0.3060 0.1743 0.4135

0.7255 0.0209 0.5238 0.0019 0.2377 0.5547 0.1454

0.1679 0.0972 0.0972 0.2375 0.2375 0.1376 0.3359

0.1428 0.0160 0.0439 0.1697 0.5518 0.6338 0.1698

0.2800 0.1560 0.1620 0.4120 0.4100 0.2320 0.5390

0.8982 0.0463 0.2412 0.1515 0.2519 0.8121 0.4488

0.3777 0.2189 0.2186 0.5341 0.5341 0.3061 0.7554

had significantly higher percentage leg quarter yield at both 18 and 24 wk than birds whose diets were changed at 4-wk intervals. Dietary amino acid levels had no significant effect on leg quarter yield at 18 wk, but there was a significant reduction in leg quarter yield at 24 wk as the amino acid level was increased above 90% of the recommended level. There were no significant interactions of amino acid level and feed change interval, strain of bird and amino acid level, strain of bird and feed change interval (data not shown), or strain of bird, amino acid level, and feed change interval (data not shown) on leg quarter yield.

1552

WALDROUP ET AL. TABLE 11. Effect of dietary amino acid level and time of changing diets on dressing percentage and abdominal fat content of two strains of male Large White turkeys

Variable

Percentage of NRC recommendations

Change interval

18-wk dressing percentage, % BUT Nicholas 3 wk 4 wk Mean 24-wk dressing percentage, % BUT Nicholas 3 wk 4 wk Mean 18-wk abdominal fat, % BUT Nicholas 3 wk 4 wk Mean 24-wk abdominal fat, % BUT Nicholas 3 wk 4 wk Mean

90%

95%

100%

105%

110%

115%

Mean

74.70 73.76 74.18 74.28 74.23

74.44 73.52 73.73 74.23 73.98

73.17 74.52 73.11 74.58 73.84

72.89 73.72 73.13 73.49 73.31

74.40 74.04 73.29 75.15 74.22

73.72 74.74 73.97 74.49 74.23

73.89 74.05 73.57 74.37

75.52 76.62 75.59 76.55 76.07

75.69 76.42 75.95 76.15 76.05

75.98 75.68 75.90 75.76 75.82

76.59 75.99 75.85 76.73 76.29

77.16 75.11 75.09 77.18 76.13

77.44 76.69 77.51 76.61 77.06

76.39 76.08 75.98 76.50

1.14 1.22 1.29 1.06 1.18

1.34 0.92 1.40 0.86 1.13

0.88 1.05 1.14 0.80 0.97

0.83 1.22 1.18 0.87 1.02

1.08 1.38 1.28 1.18 1.23

0.94 1.09 1.19 0.86 1.02

1.04 1.15 1.25r 0.94s

0.95 1.28 1.11 1.12 1.12ab

1.07 1.50 1.39 1.18 1.29a

0.94 1.41 1.27 1.08 1.18a

0.80 1.18 1.07 0.92 0.99abc

0.79 0.86 0.80 0.86 0.83bc

0.77 0.72 0.78 0.71 0.74c

0.89y 1.16x 1.07 0.98

a–cSignificant

difference among amino acid levels (P < 0.05). difference between feed change intervals (P < 0.05). x,ySignificant difference between strains of turkeys (P < 0.05). r,sSignificant

TABLE 12. Effect of dietary amino acid level and time of changing diets on breast meat and leg quarter yield of two strains of male Large White turkeys

Variable

Change interval

18-wk breast yield, % BUT Nicholas 3 wk 4 wk Mean 24-wk breast yield, % BUT Nicholas 3 wk 4 wk Mean 18-wk leg quarter yield, % BUT Nicholas 3 wk 4 wk Mean 24-wk leg quarter (yield, %) BUT Nicholas 3 wk 4 wk Mean a–fSignificant

Percentage of NRC recommendations 90%

95%

100%

105%

110%

115%

Mean

27.68 28.61 27.15 29.13 28.14c

28.40 29.79 28.62 29.57 29.10bc

28.13 30.36 28.03 30.46 29.25ab

29.17 30.46 27.84 31.79 29.81ab

29.09 29.34 28.29 30.14 29.21abc

28.97 31.17 29.64 30.51 30.07a

28.57y 29.95x 28.26s 30.27r

30.75 30.36 28.82 32.29 30.55c

30.98 33.37 31.69 32.66 32.17b

32.58 31.16 31.46 32.29 31.87bc

32.93 32.43 32.12 33.24 32.68ab

33.65 32.41 31.71 34.35 33.03ab

33.17 34.00 33.84 33.33 33.59a

32.34 32.29 31.61s 33.03r

35.23 34.58 35.57 34.24 34.90

34.65 33.80 34.42 34.04 34.23

35.15 32.86 34.32 33.70 34.00

35.55 33.08 34.51 34.12 34.31

34.29 33.77 34.95 33.11 34.02

34.73 32.66 34.14 33.25 33.69

34.93x 33.46y 34.65r 33.74s

33.60 33.97 34.89 32.68 33.78a

32.91 30.57 32.20 31.29 31.74b

32.11 32.41 32.79 31.73 32.26b

32.37 31.47 32.01 31.83 31.92b

31.64 31.59 32.18 31.05 31.61b

31.49 30.79 31.35 30.86 31.11b

32.35 31.79 32.57r 31.57s

difference among amino acid levels (P < 0.05). difference between feed change intervals (P < 0.05). x,ySignificant difference between strains of turkeys (P < 0.05). r,sSignificant

1553

AMINO ACID REQUIREMENTS OF TURKEYS TABLE 13. Effect of dietary amino acid level and time of changing diets on wing yield and skeletal rack percentage of two strains of male Large White turkeys

Variable

Change interval

18-wk wing yield, % BUT Nicholas 3 wk 4 wk Mean 24-wk wing yield, % BUT Nicholas 3 wk 4 wk Mean 18-wk skeletal rack, % BUT Nicholas 3 wk 4 wk Mean 24-wk skeletal rack, % BUT Nicholas 3 wk 4 wk Mean

Percentage of NRC recommendations 90%

95%

100%

105%

110%

115%

Mean

13.54 13.18 13.52 13.19 13.36

12.26 13.21 13.05 12.93 12.99

13.35 12.45 13.04 12.77 12.90

13.12 12.52 12.89 12.75 12.82

12.88 12.76 12.77 12.86 12.82

13.05 12.49 12.27 13.27 12.80

13.12x 12.77y 12.92 12.96

11.50 10.96 11.39abc 11.07bcde 11.23

11.27 11.19 11.11bcde 11.36abcd 11.23

10.89 11.14 10.63e 11.39abc 11.01

11.04 11.69 11.10bcde 11.63ab 11.36

11.09 11.322 11.48abc 10.93cde 11.20

11.34 11.35 10.70de 11.99a 11.35

11.19 11.28 11.07 11.40

25.33 25.28 25.47 25.13 25.30

25.49 24.92 25.82 24.59 25.20

25.10 24.21 24.98 24.33 24.66

25.75 24.78 25.87 24.66 25.26

24.97 25.26 25.45 24.78 25.12

24.75 24.12 24.10 24.77 24.44

25.23x 24.76y 25.28r 24.71s

22.56 22.14 22.95 21.75 22.35

22.16 22.09 22.26 21.99 22.12

22.19 22.73 22.56 22.37 22.46

21.56 22.58 22.22 21.92 22.07

21.66 23.36 23.67 21.35 22.51

22.27 21.72 21.74 22.25 21.99

22.07 22.44 22.57r 21.94s

a–eSignificant

difference among amino acid levels (P < 0.05). difference between feed change intervals (P < 0.05). x,ySignificant difference between strains of turkeys (P < 0.05). r,sSignificant

Wing yield was influenced by strain only at 18 wk, with wing yield of BUT poults significantly higher than wing yield of NIC poults. There was a significant effect of feed change interval on wing yield at 24 wk. However, there was also a significant interaction of amino acid level and feed change interval; there was no apparent pattern related to amino acid level and time of feed change on wing yield. There were no significant interactions of amino acid level and feed change interval, strain of bird and amino acid level, strain of bird and feed change interval (data not shown), or strain of bird, amino acid level, and feed change interval (data not shown) on wing yield. The BUT poults had significantly higher percentage skeletal rack at 18 wk than NIC poults but there was no difference between strains at 24 wk. Birds whose diets were changed at 3-wk intervals had significantly higher percentage skeletal rack at both 18 and 24 wk than those whose diets were changed at 4-wk intervals. There were no significant interactions of amino acid level and feed change interval, strain of bird and amino acid level, strain of bird and feed change interval (data not shown), or strain of bird, amino acid level, and feed change interval (data not shown) on percentage of skeletal rack.

DISCUSSION The differential response of different strains of Large White turkeys to diets of different nutrient concentrations is the object of considerable controversy. Moran et

al. (1984) subjected three commercial strains of Large White males (NIC, BUT, and Hybrid) to two different dietary regimens [North American (NA) and European Economic Community (EEC) systems]. The NA system used six feeds to 24 wk based primarily on the NRC (1977) specifications with energy increasing and protein decreasing with age. The EEC diets were more complex in ingredient makeup, utilized five feeds in the 24-wk period, and maintained a relatively constant energy level while decreasing protein. Strain by feed type interactions were not generally observed up to 12 wk; during the final 12 wk the BUT typically displayed higher weights on the EEC diets, whereas the NIC and Hybrid birds grew equally well on both regimens. Strain differences in growth rate were observed particularly between 12 and 20 wk of age, coinciding with the strain by feed type interaction. Waibel et al. (1991) utilized the same three strains of birds and compared diets formulated to nutrient standards of either NIC or BUT. Although differences were observed among strains and between diet feeding systems, they did not observe any strain by feeding system interactions. In contrast to the study by Moran et al. (1984), the dietary energy was increased with age in both feeding systems. Leeson and Caston (1991) compared NIC and BUT hens fed either a conventional NA system or a European system; the European system employed higher protein levels in early stages of

1554

WALDROUP ET AL.

growth. There were obvious differences in growth rate of the two strains of turkeys. Depending upon market age, Leeson and Caston (1991) concluded that the BUT hen seemed to respond favorably to diets of higher protein-amino acid content relative to energy concentration. However, this trend was apparent in only one of the two experiments reported. In response to individual amino acid levels, Nixey (1989) suggested that BUT birds respond favorably to increased lysine and TSAA levels in finisher diets. Lilburn (1992) subjected NIC and BUT toms to varying lysine levels between 15 and 19 wk of age and concluded that toms from the two strains were responding differently to lysine levels even though treatment differences were not significant. Lilburn and Emmerson (1993) fed NIC and BUT toms one of two series of experimental diets to 12 wk; from 12 to 24 wk all were fed the same diet. The first diet series was formulated to NRC (1984) standards whereas the second series contained heavier concentrations of lysine and TSAA (NRC+). Strain differences in performance were observed throughout the study; however, feeding the NRC+ diets enhanced performance in both strains. Results of the present study indicate no interaction of strain by amino acid levels, in agreement with the report of Waibel et al. (1991). The significant influence of feed change intervals on many of the factors related to turkey production and processing is of great economic importance and also important in comparing results from various studies related to amino acid requirements. Recommendations suggested by the NRC (1994) are based upon 4-wk feeding intervals. In two research studies evaluating NRC recommendations (Moran et al., 1995; Waibel et al., 1995) diets were changed at 3-wk intervals. In both studies, the authors indicated that the recommendations were extrapolated or adjusted for the different time interval but gave no information relating to how this adjustment was carried out. Waibel (1976) suggested that more frequent diet changes were more efficient, and diet changes at 3-wk intervals to 6 wk and every 2 wk thereafter were endorsed by Dunkelgod et al. (1961). In contrast, Nixey (1983) recommended reducing the number of diets fed and increasing the time interval of feeding each diet to improve turkey productivity. Salmon et al. (1982a) reported that frequency of changes in dietary protein concentration had little influence upon growth rate in turkeys receiving adequate dietary protein; however, a lower dietary protein was sufficient to maintain maximum growth rate when diets were changed less frequently. The results of the present study demonstrate that higher dietary amino acid levels are required to optimize performance when diet changes are made at more frequent intervals. Interpretation of data related to amino acid requirements of turkeys should consider length of feeding interval involved in relation to NRC (1994) recommendations.

Recommendations for protein and amino acid needs of turkeys must consider environmental temperatures (Hurwitz et al., 1980; Oju et al., 1987; Noll and Waibel, 1989). Ambient temperatures in the present study exceeded 28 C from 10 to 20 wk (Figure 1) and may have contributed to the need for somewhat greater amino acid levels than the present NRC (1994) suggestions, especially during the 12 to 18 wk period. The results of the present study indicated that the amino acid levels suggested by the NRC (1994) are adequate to support maximum body weight gains, feed conversion, and dressing percentage of male Large White turkeys grown to 18 or 24 wk of age when fed at the 4-wk intervals suggested by NRC (1994). An approximately 5% higher level of amino acids was required to maximize breast meat yield. Considering the relatively high temperatures encountered during this study, the levels recommended by NRC (1994) are probably adequate for all parameters under temperate environmental conditions. Although the two strains of turkeys used in this study differed in their growth patterns, there did not appear to be any difference in the response of these two commercial strains of turkeys to different levels of amino acids in this study.

ACKNOWLEDGMENTS The authors express their thanks to Nicholas Turkey Breeding Farms, Sonoma, CA 95476 and British United Turkeys, Lewisburg, WV 24901 for providing the poults used in this study. Lysine and threonine were kindly provided by BioKyowa, Chesterfield MO 63017. Analysis of total and free amino acids were conducted courtesy of the Degussa Corp., Allendale, NJ 07401.

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