3Arbor Acres Farm, Inc., Albertville, AL 35950. 4Heartland Animal Health, Fair Play, MO 65649. 5Petersime Incubator Co., Gettysburg, OH 54238. 6Bloom 175 ...
Tryptophan Requirements of Different Broiler Genotypes A. P. Rosa,1 G. M. Pesti,2 H. M. Edwards, Jr., and R. Bakalli Department of Poultry Science, University of Georgia, Athens, Georgia 30602-2772 ABSTRACT Two experiments were conducted with broiler chicks in battery brooders from 1 to 18 d of age to determine Trp requirements and to evaluate the performance of different genotypes (classic vs. high yield and male vs. female). Experiment 1 was a 6 × 2 factorial experiment, with six levels of Trp (0.09, 0.12, 0.15, 0.18, 0.21, and 0.24% of the diet) and two broiler chicken strains (male Arbor Acres Classic and Arbor Acres High Yield). Experiment 2 was a 6 × 2 factorial design with the same levels of Trp as in Experiment 1 and two sexes (males and females); Ross × Ross 308 birds were used. Both experiments had four replicate pens of eight birds each per treatment. The basal diet was based on corn (70.79%), corn gluten meal (17.44%), and gelatin by-product and poultry fat (23% of CP and 3.34 kcal/g of ME). At 18 d
of age, three birds per replicate were killed, and livers and fat pads were removed. The broken-line linear model was used to estimate the chicks Trp requirement. Liver or liver fat and fat pad weights (as a percentage of body weight) were affected by dietary Trp level. In Experiment 1, the Trp requirements differed little; for gain they were 0.18 ± 0.002% and 0.17 ± 0.002%, and for feed conversion they were 0.16 ± 0.004% and 0.16 ± 0.002%, for the Classic and High Yield broilers, respectively. In Experiment 2, the Trp requirement of males was 0.17 ± 0.003% for BW and 0.17 ± 0.003% for feed conversion, and that of females was 0.17 ± 0.003% for body weight and 0.16 ± 0.001% for feed conversion. There was no apparent difference in the Trp requirement of young broilers due to genetic stock or gender (P > 0.05).
(Key words: tryptophan, genotype, requirement, broiler) 2001 Poultry Science 80:1718–1722
INTRODUCTION Genetic selection has significantly altered the productive performance and carcass composition of birds. The nutritional requirements of the new genotypes have been altered. In broiler chickens, responses to CP, metabolizable energy, calcium, and phosphorous levels have been studied. Many research reports demonstrated significant differences in nutritional requirements attributable to different genotypes (Siegel et al., 1984; Leclercq and Guy, 1991; Ajang et al., 1993; Leclercq et al., 1993; Pesti et al., 1994, 1996; Smith and Pesti, 1998; Smith et al., 1998) and sexes (Sebastian et al., 1997). Information about essential amino acid requirements is extremely important for feed formulation. Tryptophan is an essential amino acid for chickens. Generally, it is classified as the third or fourth limiting amino acid for broilers. Besides being essential for protein synthesis, Trp has many roles in the metabolism of chickens, such as the conversion to niacin and the precursor of serotonin
2001 Poultry Science Association, Inc. Received for publication February 28, 2001. Accepted for publication July 9, 2001. 1 Animal Science Department of Federal University of Santa Maria, UFSM, Santa Maria, RS, and CAPES Foundation, Brazil. 2 To whom correspondence should be addressed: gpesti@arches. uga.edu.
and melatonin (Briggs et al., 1946). More recently it was demonstrated that Trp can affect lipid levels in chickens (Akiba et al., 1988; Rogers and Pesti, 1990). The Trp requirement to minimize lipid levels is almost double that to maximize body growth of broilers (Rogers and Pesti, 1990). There is little information in the literature about Trp requirements for broilers, and some of the results are controversial. West et al. (1952) and Childs et al. (1952) found the Trp requirement for birds to be 0.19% of the diet. Fischer et al. (1955) showed that birds need diets with only 0.15% of Trp. Klain et al. (1960) and Hewitt and Lewis (1972) estimated that the ideal level is 0.17% of the diet. Woodham and Deans (1975) found that the requirement of Trp is around 0.14% of the diet. Freeman (1979) determined that requirements for males and females, from 0 to 7 d of age, are 0.24 to 0.22% of the diet. Smith and Waldroup (1988) estimated that the requirement of Trp for male broilers, from 1 to 20 d of age, is not greater than 0.16%. The level of Trp recommended for broiler chickens by the NRC (1994), from 0 to 3 wk of age, is 0.20% of the diet. Cole and Van Lunen (1994) and Larbier and Leclercq (1994) determined that the Trp requirement, expressed
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Abbreviation Key: BWG = body weight gain.
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TRYPTOPHAN REQUIREMENT OF BROILER GENOTYPES
in relation to the Lys level of the diet is 19.2% and 18.0%, respectively. The experiments reported here were conducted to determine the Trp requirement and to evaluate the effects of dietary Trp levels on performance of two broiler genotypes (Classic vs. High Yield strain) and male vs. female genotypes of a different High Yield strain.
MATERIALS AND METHODS Eggs from two broiler breeder strains, Classic and High Yield were obtained from the breeder3 for Experiment 1. The broiler breeders were the same age and were fed the same diets and kept under the same management conditions. The strains were chosen because they are known to have different carcass compositions. The eggs were incubated together using standard procedures. The chicks were selected based on healthy appearance and sexed by inspection of the vent. Only males were used for this experiment. The birds were weighed, neckbanded,4 and placed on wire floors in Petersime battery brooders5 in a temperature-controlled room with constant illumination from 1 to 18 d of age. Feed and water were provided ad libitum. Mortality was recorded daily. Feed consumption data were adjusted to account for any deaths on a chick-day basis. At 18 d of age, all chicks of each replicate were individually weighed, and three birds per replicate were killed by cervical dislocation. Abdominal fat pads and livers were removed and weighed. Liver lipids were measured according to the method of Folch et al. (1957). The tibiae were removed, and tibia ash was measured in Experiment 1 by the method of the AOAC (1995). Experiment 1 had a factorial design with six levels of Trp (0.12, 0.15, 0.18, 0.21, 0.24, and 0.27% of the diet) and two strains (Arbor Acres Classic and High Yield) with four replicate pens of eight birds each per treatment. The Experiment 2 also had a 6 × 2 factorial design with six levels of Trp (as Experiment 1) and two sexes. Ross × Ross 308 chicks were obtained from a commercial hatchery. Feather-sexed, male and female chicks were used. The procedures in Experiment 2 were the same as for Experiment 1. The basal diets (Table 1) were based on corn, corn gluten meal, gelatin by-product,6 poultry fat, DL-Met, LLys, L-Arg, and L-Thr (23% CP and 3.34 kcal of metabolizable energy/g of diet). The data were analyzed by the general linear model and nonlinear model procedures of SAS software (1996). Means were separated using Duncan’s new multiplerange test. The broken-line linear model was used to estimate chick amino acid requirements as follows: Response = max + rc × (req − x) × I, where max = plateau, rc = rate
3
Arbor Acres Farm, Inc., Albertville, AL 35950. Heartland Animal Health, Fair Play, MO 65649. 5 Petersime Incubator Co., Gettysburg, OH 54238. 6 Bloom 175 (1995), United States Biochemical Corp., Cleveland, OH 44128. 4
TABLE 1. Composition of the basal diet (Experiments 1 and 2) Composition (%)
Ingredients Corn, grain Corn gluten meal Gelatin by-product Poultry fat Defluorinate phosphate Limestone L-Lys L-Arg HCl L-Thr DL-Met Common salt Vitamin premix1 Mineral premix2 Zinc bacitracin Total Composition from table values3 Crude protein (%) Metabolizable energy (kcal/g) Ether extract (%) Calcium (%) Available phosphorous (%) Arg (%) Lys (%) Met (%) Met + Cys (%) Thr (%) Trp (%) Val (%) Composition by analysis Crude protein4 (%) Trp5 (%)
70.79 17.44 5.00 2.00 1.92 0.71 0.75 0.34 0.19 0.08 0.40 0.25 0.08 0.05 100.00 23.00 3.34 5.12 0.90 0.45 1.25 1.10 0.57 0.90 0.80 0.09 0.90 Experiment 1
Experiment 2
23.29 0.12
24.62 0.12
1 Vitamin premix provided the following per kilogram: Vitamin A, 5,500 IU from all trans-retinyl acetate, cholecalciferol, 1,100 IU; vitamin E, 11 IU from all-rac-α-tocopherol acetate; riboflavin, 4.5 mg; Ca pantothenate, 12 mg; nicotinic acid, 44 mg; choline Cl, 220 mg; vitamin B12, 6.6 µg; Vitamin B6, 2.2 mg; menadione, 1.1 mg (as menadione sodium bisulfate); folic acid, 0.55 mg; d-biotin, 0.11 mg; thiamine, 1.1 mg (as thiamine mononitrate); ethoxyquin, 125 mg. 2 Trace mineral premix provided the following in milligrams per kilogram of diet: Mn, 60; Zn, 50; Fe, 30; Cu, 5; I, 1.5; Se, 1.0. 3 NRC (1994). 4 Dumas method (Etheridge et al., 1998). 5 Experiment Station Chemical Laboratories, University of MissouriColumbia, Columbia, MO 65211, AOAC Official Method 988.15, CHP 45.4.04 (1995).
constant, req = requirement, x = level, and I = 1 when x < req, otherwise I = 0.
RESULTS AND DISCUSSION The determined Trp values for the basal diets in both experiments (Table 1) were higher (0.12 vs. 0.09%) than what was predicted from ingredient composition tables (NRC, 1994). Clearly, requirement estimates should be highly dependent on accurate estimates of dietary Trp. The basal diet was clearly deficient in Trp (Tables 2 and 3). Approximately five- and fourfold increases in growth were observed by supplementing Trp in Experiments 1 and 2, respectively. Curvilinear (quadratic) responses to dietary Trp level were observed for body weight gain (BWG), feed consumption and efficiency, percentage abdominal fat pads, and percentage liver fat in both experiments (P≤ 0.10). Percentage liver was also af-
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ROSA ET AL. TABLE 2. Influence of dietary Trp level on the performance of male Arbor Acres Classic and High Yield broiler chickens from 0 to 18 d of age (Experiment 1)1 Feed consumption (g)
Strain
n
Classic Classic Classic Classic Classic Classic High Yield High Yield High Yield High Yield High Yield High Yield
0.12 0.15 0.18 0.21 0.24 0.27 0.12 0.15 0.18 0.21 0.24 0.27
4 4 4 4 4 4 4 4 4 4 4 4
177 382 527 541 522 571 220 483 570 584 570 590
± ± ± ± ± ± ± ± ± ± ± ±
3 31 20 18 9 28 6 20 14 8 25 6
70 221 374 394 384 389 98 290 405 413 418 431
± ± ± ± ± ± ± ± ± ± ± ±
6 19 13 12 8 7 4 8 11 4 12 6
2.58 1.73 1.41 1.37 1.36 1.47 2.24 1.67 1.41 1.41 1.36 1.37
± ± ± ± ± ± ± ± ± ± ± ±
0.20 0.03 0.01 0.01 0.01 0.06 0.04 0.05 0.02 0.02 0.04 0.01
0.29 1.11 1.22 1.32 1.34 1.25 0.45 1.48 1.59 1.39 1.52 1.46
± ± ± ± ± ± ± ± ± ± ± ±
0.10 0.23 0.03 0.11 0.16 0.06 0.06 0.21 0.04 0.07 0.15 0.08
2.87 3.48 3.49 3.43 3.52 3.38 3.29 3.64 3.43 3.49 3.37 3.61
± ± ± ± ± ± ± ± ± ± ± ±
0.16 0.22 0.11 0.07 0.11 0.21 0.15 0.10 0.12 0.07 0.06 0.04
3.93 4.75 5.05 4.95 3.92 4.40 4.34 4.98 5.22 4.48 5.04 4.94
± ± ± ± ± ± ± ± ± ± ± ±
0.17 0.68 0.57 0.35 0.23 0.43 0.26 0.42 0.70 0.15 0.22 0.43
Main effect means Both Both Both Both Both Both Classic High Yield
0.12 0.15 0.18 0.21 0.24 0.27 All All
8 8 8 8 8 8 12 12
198 433 548 563 546 581 453 502
± ± ± ± ± ± ± ±
9c 25b 14a 12a 15a 14a 29.56b 27.94a
84 255 390 404 401 410 305 343
± ± ± ± ± ± ± ±
6c 16b 10a 7a 9a 9a 26b 25a
2.41 1.70 1.41 1.39 1.36 1.42 1.65 1.58
± ± ± ± ± ± ± ±
0.01a 0.02b 0.01c 0.01c 0.02c 0.03c 0.09b 0.06b
0.37 1.30 1.40 1.35 1.43 1.36 1.09 1.32
± ± ± ± ± ± ± ±
0.06b 0.15b 0.07a 0.06a 0.10a 0.06a 0.08 0.09
3.08 3.56 3.46 3.46 3.45 3.50 3.36 3.47
± ± ± ± ± ± ± ±
0.12b 0.11a 0.07a 0.04a 0.06a 0.10a 0.07 0.04
4.13 4.86 5.14 4.72 4.48 4.67 4.50 4.84
± ± ± ± ± ± ± ±
0.16 0.37 0.42 0.19 0.25 0.30 0.18 0.16
Analysis of variance Source Strain Trp Trp × Trp Trp × strain
BW gain (g)
Feed conversion (g/g)
Trp (%)
Fat pad (%)
Liver (%)
Liver fat (%)
df 1 1 1
0.0011 0.0001 0.0001 0.3468
0.0001 0.0001 0.0001 0.7983
0.0498 0.0001 0.0001 0.1210
0.2537 0.0001 0.0001 0.7378
0.1643 0.0268 0.0490 0.3050
0.9138 0.0846 0.0923 0.5907
a–c Values with no common superscript differ significantly (P < 0.05) when tested with Duncan’s new multiple-range test following analysis of variance. 1 Values as mean ± standard errors of n replicate pens of eight birds each.
TABLE 3. Influence of dietary Trp levels on the performance of Ross × Ross 308 male and female broiler chickens and variance analysis from 0 to 18 d of age (Experiment 2)1 Feed consumption (g)
Sex
n
Males Males Males Males Males Males Females Females Females Females Females Females
0.12 0.15 0.18 0.21 0.24 0.27 0.12 0.15 0.18 0.21 0.24 0.27
4 4 4 4 4 4 4 4 4 4 4 4
225 469 604 557 585 572 235 480 618 589 562 566
± ± ± ± ± ± ± ± ± ± ± ±
12 13 20 10 4 18 2 27 17 10 14 10
110 301 423 407 418 430 108 286 432 415 399 410
± ± ± ± ± ± ± ± ± ± ± ±
8 7 12 7 8 22 3 23 18 8 6 10
2.05 1.56 1.43 1.37 1.40 1.34 2.17 1.69 1.44 1.42 1.41 1.38
± ± ± ± ± ± ± ± ± ± ± ±
0.09 0.02 0.02 0.01 0.03 0.03 0.07 0.05 0.04 0.01 0.05 0.02
0.60 1.58 1.41 1.29 1.43 1.27 0.80 1.56 1.60 1.46 1.52 1.53
± ± ± ± ± ± ± ± ± ± ± ±
0.18 0.15 0.05 0.11 0.11 0.08 0.04 0.13 0.10 0.06 0.09 0.12
3.18 3.16 3.06 3.11 3.27 3.18 3.13 3.33 3.40 3.22 3.38 3.59
± ± ± ± ± ± ± ± ± ± ± ±
0.13 0.07 0.08 0.09 0.09 0.06 0.03 0.08 0.06 0.08 0.06 0.22
4.44 4.14 5.18 4.81 4.70 5.00 4.72 4.78 6.11 5.55 5.36 5.03
± ± ± ± ± ± ± ± ± ± ± ±
0.49 0.31 0.25 0.35 0.26 0.24 0.03 0.36 0.29 0.64 0.45 0.18
Main effect means Males Females Both Both Both Both Both Both
All All 0.09 0.12 0.15 0.18 0.21 0.24
12 12 8 8 8 8 8 8
502 508 230 474 611 573 573 569
± ± ± ± ± ± ± ±
28 29 6d 12c 13a 9b 8b 10b
348 342 109 294 427 411 408 420
± ± ± ± ± ± ± ±
24 25 4c 10b 10a 5a 6a 12a
1.52 1.58 2.11 1.62 1.43 1.39 1.41 1.36
± ± ± ± ± ± ± ±
0.05 0.06 0.05a 0.03b 0.02c 0.01c 0.02c 0.01c
1.26 1.41 0.70 1.57 1.50 1.37 1.47 1.40
± ± ± ± ± ± ± ±
0.07 0.06 0.09b 0.09a 0.06a 0.06a 0.07a 0.08a
3.16 3.34 3.16 3.25 3.23 3.17 3.32 3.39
± ± ± ± ± ± ± ±
0.03 0.05 0.06 0.05 0.08 0.05 0.05 0.13
4.71 5.26 4.58 4.46 5.65 5.18 5.03 5.01
± ± ± ± ± ± ± ±
0.13 0.17 0.23b 0.25b 0.24a 0.36ab 0.27ab 0.13ab
Analysis of variance Source Sex Trp Trp × Trp Trp × sex
df 1 1 1 1
0.5641 0.0001 0.0001 0.6181
BW gain (g)
Feed conversion (g/g)
Trp (%)
0.8171 0.0001 0.0001 0.6643
0.0856 0.0001 0.0001 0.2350
Fat pad (%)
0.9554 0.0001 0.0001 0.6326
Liver (%)
0.5298 0.5735 0.3847 0.1069
Liver fat (%)
0.2531 0.0279 0.0423 0.7028
a,b Values with no common superscript differ significantly (P < 0.05) when tested with Duncan’s new multiple-range test following analysis of variance. 1 Values are means ± standard errors of n replicate pens of eight birds each.
TRYPTOPHAN REQUIREMENT OF BROILER GENOTYPES
FIGURE 1. Estimated Trp requirements and coefficients of determination for body weight gain for male Arbor Acres Classic and High Yield broilers (1 to 18 d of age) fitted by the broken-line linear model (Experiment 1).
fected by Trp level in Experiment 1 but not in Experiment 2. Differences between the Classic and High Yield genotypes were observed for BWG and feed consumption and efficiency (Table 2). However, no differences were noted for male vs. female genotypes due to dietary Trp levels (Table 3). We found no interactions of Trp level by genotype in either experiment. In Experiment 1 the Trp requirements for gain were 0.18 ± 0.002% and 0.17 ± 0.002%, for Classic and High Yield strains, respectively (P < 0.05; Figure 1). The levels of Trp required based on minimizing feed conversion (Figure 2) were 0.16 ± 0.004% for Classic and 0.16 ± 0.002% for High Yield strain broilers (P > 0.05).
FIGURE 2. Estimated Trp requirements and coefficients of determination for feed conversion for male Arbor Acres Classic and High Yield broilers (1 to 18 d of age) fitted by the broken-line linear model (Experiment 1).
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FIGURE 4. Estimated Trp requirements and coefficients of determination of male and female Ross × Ross 308 broilers for feed conversion (1 to 18 d of age) fitted by the broken-line linear model.
In Experiment 2, the Trp requirements of the males and females for body gain were essentially the same, 0.17 ± 0.003% (Figure 3). The Trp requirements for feed conversion were 0.16 ± 0.003% for males and 0.17 ± 0.001% for females (Figure 4); these values did not differ significantly (P > 0.05). The broken-line model used here (Figures 1 to 4) often yielded very small standard errors for requirement estimates, ±0.001 to ±0.004% Trp. However, the accuracy of the analytical results is no greater than the nearest 0.01% Trp. Therefore, requirement estimates are presented here with two decimal places, but the standard errors with three decimal places. Results from the broken-line model have been very consistent across the two experiments and genotypes for this type of biological assay. Genetic differences in the responses to dietary protein level (Leclercq and Guy, 1991; Ajang, 1993; Smith and
FIGURE 3. Estimated Trp requirements and coefficients of determination of male and female Ross × Ross 308 broilers for body weight gain (1 to 18 d of age) fitted by the broken-line linear model (Experiment 2).
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ROSA ET AL.
Pesti, 1998; Smith et al., 1998) and individual amino acids (Leclercq et al., 1993; Pesti et al., 1994, 1996) have been demonstrated. The results of Experiments 1 and 2 suggested no important differences in Trp responses or requirements among commercial broiler chickens selected for high meat yields or any differences that were due to gender. Of course, not all commercial stocks were tested, but only a very small sample. It is entirely possible that strains beginning with different genetic material and selected for different criteria have been, or could be, produced with higher or lower Trp requirements. It is interesting to note that differences in carcass lipids due to Trp level observed by Akiba et al. (1998) and Rogers and Pesti (1990) were not observed in Experiments 1 and 2. Genetic differences may be responsible for differences between experiments. In the earlier experiments, carcass lipids decreased when Trp was fed above requirement levels. In the present experiments, significant responses observed were increases in fat pads with increases in Trp level that paralleled changes in BWG (Tables 2 and 3). The overall conclusion of these experiments is that no more than 0.18% Trp is needed by starting broiler chickens, regardless of genotype. Similar results were found for Arbor Acres Classic and High Yield, and Ross × Ross 308 male vs. female genotypes. This conclusion is very similar to the research results of Fischer (1955), Smith and Waldroup (1988), Cole and Van Lunen (1994), Larbier and Leclercq (1994), and the NRC (1994) recommendation of 0.20% Trp.
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