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Evaluation of tryptophan requirement of the commercial layer by using a corn-soybean meal basal diet1
Evaluation of Tryptophan Requirement of the Commercial Layer by Using a Corn-Soybean Meal Basal Diet1 R. H. Harms2 and G. B. Russell Department of Dairy and Poultry Science, University of Florida, Gainesville, Florida 32611 ABSTRACT An experiment was conduced with HyLine W36威 hens to evaluate the requirement for Trp in a corn-soybean meal diet. Seven experimental diets were fed with Trp levels of 0.12, 0.13, 0.14, 0.15, 0.16, 0.17 and 0.18%. Supplemental amino acids (AA) were added to all diets to ensure that Trp was the first-limiting AA. A positive control diet (0.20% Trp) with Met supplementa-
tion was fed that had previously been shown to support maximum performance. Egg production (EP), egg weight (EW), and egg content (EC) were significantly increased by the addition of Trp to the basal diet. Broken-line regression indicated the Trp requirement for EP and EC was 139.8 and 149.0 mg per hen/d, respectively, for EP and EC when hens had a daily EC of 45.4 g per hen/d.
(Key words: commercial layer, tryptophan, egg production, egg content)
the growing period was formulated according to the specifications of Harms and Douglas (1984). Pullets were given 12 h of light during the growing period, and at 18 wk of age were moved to a windowless layer house with tunnel ventilation and given 16 h of artificial light. Hens were randomly placed, one per cage in groups of five cages, and were given the diet containing 0.20% Trp (Table 1). The temperature of the house was not allowed to fall below 26.7 C. The experiment was conducted in December and January, and temperature seldom reached 29.4 C. The temperature was controlled to achieve uniform feed intake at a level that a Trp deficiency could be produced. Eight experimental diets were fed (Table 1). The control diet contained 0.20% Trp and levels of other AA were known to support maximum performance (Harms and Russell, 1996). A second diet was used that contained 0.18% Trp and AA levels that were expected to support maximum egg production (EP). Six other diets were formulated to supply 0.12, 0.13, 0.14, 0.15, 0.16, and 0.17% Trp. The other AA were not reduced when the Trp was reduced from 0.18 to 0.17%. The other five diets were formulated in a similar manner. This formulation resulted in the other AA being higher than required and Trp being first limiting. The AA analysis of diets was based on analysis of corn and soybean meal. Tryptophan analysis was made according to the procedure described by Jensen et al. (1990). Eight replicates of five hens were fed each diet. Egg production was recorded for individual hens but was analyzed on a replicate basis. Feed consumption was
INTRODUCTION As soybean meal is replaced with corn in the diet, Met becomes limiting and can be supplied by synthetic Met (Harms and Waldroup, 1963). When more soybean meal is replaced with corn, Lys becomes limiting (Harms and Waldroup, 1963). However, Lys HCl is not routinely used because we do not have a good estimate for the Trp requirement, which is the next limiting amino acid (AA). In most of the previous research, a variety of ingredients were used to provide a diet deficient in Trp. Morris and Wethli (1978) and Wethli and Morris (1978) used a diet containing maize gluten meal, herring meal, starch, gelatin, and cerelose. The diet Jensen et al. (1990) used contained corn gluten meal, meat and bone meal, and poultry by-product meal. More recently Russell and Harms (1999) used a corn-soybean meal diet containing 2% gelatin. Bray (1969) used a basal diet with 8.5% protein and 60% of the protein from corn and 40% from soybean meal. The present experiment was conducted with a cornsoybean meal diet supplemented with AA sufficient to obtain maximum performance.
MATERIALS AND METHODS Hy-Line W36威3 hens, grown in a dark-out house with pine shavings used as litter, were used. The feed during
Received for publication June 30, 1999. Accepted for publication January 28, 2000. 1 Florida Agricultural Experiment Station Journal Series Number R06950. 2 To whom correspondence should be addressed: Harms@dps. ufl.edu. 3 Hy-Line International, West Des Moines, IA 50265.
Abbreviation Key: AA = amino acids; EC = egg content; EP = egg production; EW = egg weight.
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2000 Poultry Science 79:740–742
741
TRYPTOPHAN REQUIREMENT OF COMMERCIAL LAYERSRESEARCH NOTE
RESULTS AND DISCUSSION Egg production increased from 66.2% with hens receiving the diet containing 0.12% Trp to 92.7% when the diet
contained 0.17% Trp (Table 2). The EP from hens receiving the diet with 0.17% Trp was equal to the EP of hens receiving the practical diet with 0.20% Trp. Broken-line regression [y = 92.24 + 0.4352(x − 139.8); R2 = 0.95] of EP on Trp intake resulted in a Trp requirement of 139.8 ± 1.9 mg/hen per d. Egg weight increased from 49.7 g when the diet contained 0.12% Trp to 54.8 g when the diet contained 0.20% Trp (Table 2). However, increase of the level of Trp above 0.18% did not increase EW significantly. Broken-line regression [y = 55.01 + 0.0474 (x − 185.6); R2 = 0.73] of EW on Trp intake resulted in a Trp requirement of 185.6 ± 11.42 mg/hen per d. The finding that EW increased as dietary Trp increased does not agree with previous reports (Ohtani et al., 1989; Jensen et al., 1990; Russell and Harms, 1999). In previous studies, a basal diet was used, and graded levels of Trp were added to the basal. In the present study, the level of Trp was obtained by varying the level of protein and adding other AA to furnish levels that resulted in Trp being the first limiting. The increase in egg content (Table 2) followed the same trend as EP and EW when Trp was increased. However, the increase from increasing the Trp level was 51% for EC, 11% for EW, and 39% for EP. Broken-line regression [y = 45.45+ 0.2203 (x − 149.0); R2 = 0.96] of EC on Trp intake indicated a requirement of 149.0 ± 1.9 mg/hen per d. Feed consumption increased as the level of Trp increased (Table 2). This increase was a result of an increased energy requirement as the output of EC increased.
TABLE 1. Composition of diets Trp content (%) Ingredients
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.20
(%) Yellow corn Soybean meal (48%) Limestone Dicalcium phosphate1 Vitamin mix2 Mineral mix3 Salt DL-Methionine Lysine-HCl Arginine Threonine Valine Isoleucine Calculated analysis (%)4 Protein Methionine Lysine Threonine Valine Isoleucine Arginine Kcal ME/kg 1
78.730 10.700 7.872 1.423 0.250 0.250 0.326 0.042 0.179 0.096 0.050 0.043 0.039 11.26 0.24 0.62 0.44 0.56 0.46 0.73 2,916
77.125 12.312 7.879 1.393 0.250 0.250 0.326 0.056 0.175 0.098 0.056 0.042 0.038 11.90 0.26 0.66 0.47 0.59 0.49 0.78 2,901
75.520 13.925 7.892 1.363 0.250 0.250 0.326 0.069 0.172 0.099 0.062 0.041 0.037 12.53 0.28 0.70 0.50 0.62 0.52 0.83 2,888
73.915 15.537 7.892 1.334 0.250 0.250 0.327 0.082 0.169 0.101 0.069 0.040 0.035 13.17 0.30 0.74 0.53 0.65 0.55 0.88 2,874
72.311 17.149 7.898 1.304 0.250 0.250 0.327 0.095 0.166 0.102 0.075 0.039 0.033 13.80 0.32 0.78 0.56 0.68 0.58 0.93 2,860
70.706 18.761 7.905 1.274 0.250 0.250 0.327 0.108 0.162 0.104 0.081 0.039 0.033 14.44 0.34 0.82 0.59 0.71 0.61 0.98 2,846
69.478 20.341 7.914 1.240 0.250 0.250 0.326 0.101 0.108 ... ... ... ... 14.70 0.34 0.82 0.54 0.70 0.61 0.93 2,831
66.356 23.567 7.928 1.179 0.250 0.250 0.326 0.143 ... ... ... ... ... 15.88 0.40 0.82 0.58 0.77 0.67 1.02 2,803
Contains 18.5% P and 21% Ca. Supplies per kilogram of diet: biotin, 0.2 mg; cholecalciferol, 2,200 IU; choline, 500 mg; ethoxyquin, 65 mg; folic acid, 1 mg; niacin, 60 mg; pantothenic acid, 15 mg; pyridoxine, 5 mg; riboflavin, 5 mg; thiamin, 3 mg; vitamin A, 8,000 IU; vitamin B12, 0.02 mg; vitamin E, 20 IU; and vitamin K, 2 mg. 3 Supplies per kilogram of diet: copper, 10 mg; ethoxyquin, 65 mg; iodine, 2 mg; iron, 60 mg; manganese, 90 mg; selenium, 0.2 mg; zinc, 80 mg. 4 Based on analysis of corn and soybean meal. 2
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measured biweekly, and feed was replaced with fresh feed at that time. One egg from each hen that was laid on the last 2 d of each wk was weighed. Then those eggs were broken out; the shells were washed, allowed to dry, and weighed. Egg mass was calculated by multiplying percentage EP by egg weight (EW) for each replicate. Egg content (EC) was calculated by multiplying EP by EW minus shell weight. The hens were individually weighed at the beginning and end of the experiment, and weight gain was calculated. The daily intake of Trp and energy was calculated by multiplying the amount in the feed by feed consumption. The kilocalories of energy and milligrams of Trp per gram of EC was calculated by dividing the daily intake of energy and Trp by daily EC. The experiment was started at 28 wk of age and continued until 8 wk. However, the first 2 wk were considered as a depletion period and Weeks 3 to 8 were used to test experimental treatments. We use this procedure in our laboratory (Russell and Harms, 1999). The data were subjected to ANOVA with the general linear model procedure of SAS (1988). Duncan’s multiplerange test (1955) was used to determine significant differences among treatment means. The hen requirement for Trp for EP, EC, and BW change was determined by using broken-line regression as described by Noll and Waibel (1989).
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HARMS AND RUSSELL TABLE 2. Performance of commercial laying hens receiving diets with various levels of Trp Egg content (EC)
Dietary Trp
Egg production
Egg weight
(%) 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.20
(%) 66.2e 75.0d 83.6c 88.1b 89.5ab 92.7a 92.7a 92.3a
(g)
(g)
49.7e 51.6e 52.0de 52.0de 52.8cd 53.6bc 54.0ab 54.8a
29.9e 35.1d 39.4c 41.5b 42.9b 45.1a 45.2a 45.2a
Trp Intake Feed consumption
Energy intake
BW Change
Daily
(g/h/d)
(g)
(mg/h/d)
(mg)
kcal
kcal
68.0d 75.2c 84.9b 88.7ab 88.7ab 89.6ab 92.6a 90.8a
−192d −123c −16b 52.3a 67.3a 71.9a 98.1a 83.9a
81.4g 97.8b 118.9e 133.0d 142.0c 157.5b 161.4b 181.7a
2.74e 2.80e 3.07d 3.20c 3.31c 3.49b 3.57b 3.94a
197d 218c 245b 255ab 254ab 264a 254ab 255ab
6.67a 6.24b 6.22b 6.14bc 5.91cd 5.85d 5.62e 5.52e
g/EC
h/d
g/EC
a–e
Means within a column with a different superscript differ significantly.
ACKNOWLEDGMENT Financial support from Novus International Inc., St. Louis, MO 63304, is gratefully acknowledged.
REFERENCES Bray, D. J., 1969. Studies with corn-soy laying diets. 8. Requirements for limiting amino acids—the basal diet and the requirements for isoleucine, lysine, and tryptophan. Poultry Sci. 48:674–684. Coon, G., and B. Zhang, 1999. Ideal amino acid profile for layers examined. Feedstuffs 71(14):13–15, 31. Duncan, D. B., 1955. Multiple range and multiple F test. Biometrics 11:1–42. Harms, R. H., and C. R. Douglas, 1984. Amino acids, mineral needs for replacement pullets modified. Feedstuffs 56(26):16–17. Harms, R. H., and G. B. Russell, 1996. A re-evaluation of the methionine requirement of the commercial layer. J. Appl. Anim. Res. 9:141–151. Harms, R. H., G. B. Russell, H. Harlow, and F. J. Ivey, 1997. Performance of laying hens fed three levels of methionine in diets containing two levels of protein and energy. J. Appl. Poult. Res. 7:45–52. Harms, R. H., and P. W. Waldroup, 1963. Methionine hydroxy analogue and lysine supplementation of low-protein laying diets. Br. Poult. Sci. 4:267–273. Jensen, L. S., V. M. Calderon, and C. X. Mendonca, Jr., 1990. Response to tryptophan of laying hens fed practical diets varying in protein concentration. Poultry Sci. 69:1956–1965. Morris, T. R., and E. Wethli, 1978. The tryptophan requirement of young laying pullets. Br. Poult. Sci. 19:455–466. Noll, S. L., and P. E. Waibel, 1989. Lysine requirement of the growing turkey in various temperature environments. Poultry Sci. 68:781–794. Ohtani, H., S. Saitoh, H. Ohkawara, Y. Akiba, K. Takahashi, M. Horiguchi, and K. Goto, 1989. Research note: Production performance of laying hens fed L-tryptophan. Poultry Sci. 68:323–326. Russell, G. B., and R. H. Harms, 1999. Tryptophan requirement of the commercial laying hens. Poultry Sci. 78:1283–1285. SAS Institute, 1988. SAS威 User’s Guide: Statistics. SAS Institute Inc., Cary, NC. Wethli, E., and T. R. Morris, 1978. Effects of age on the tryptophan requirement of laying hens. Br. Poult. Sci. 19:559–565.
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The energy consumed per gram of EC decreased from 6.67 kcal when the diet contained 0.12% Trp to 5.52 kcal when the diet contained 0.20% Trp. There was no significant difference in the amount of energy consumed per gram of EC when the diets contained 0.18 or 0.20% Trp. The decrease in energy required to produce a gram of EC became progressively less as the level of Trp increased. This finding agrees with the relationship of energy consumed as EC increased when the level of Met was increased in the diet (Harms et al., 1997). Body weight change was not significantly different among hens that received diets containing 0.15 to 0.20% Trp (Table 2). Reduction of Trp from 0.15 to 0.14% resulted in a significant difference in BW change. Further significant reductions in BW occurred when Trp was reduced to 0.13 or 0.12%. The daily Trp intake increased each time the Trp was increased. This result was largely due to the increase in Trp content in the diet. However, a portion of the increase resulted from an increase in feed intake as the Trp content of the diet increased. The Trp intake per gram of EC increased as the Trp content of the diet increased (Table 2). It has been reported that the Met intake per gram of EC increases as the daily output of EC increases (Harms et al., 1997). An average of 3.67 mg of Trp was required per gram EC for hens consuming the diets with the three highest levels of AA.
tion was fed that had previously been shown to support maximum performance. Egg production (EP), egg weight (EW), and egg content (EC) were significantly increased by the addition of Trp to the basal diet. Broken-line regression indicated the Trp requirement for EP and EC was 139.8 and 149.0 mg per hen/d, respectively, for EP and EC when hens had a daily EC of 45.4 g per hen/d.
(Key words: commercial layer, tryptophan, egg production, egg content)
the growing period was formulated according to the specifications of Harms and Douglas (1984). Pullets were given 12 h of light during the growing period, and at 18 wk of age were moved to a windowless layer house with tunnel ventilation and given 16 h of artificial light. Hens were randomly placed, one per cage in groups of five cages, and were given the diet containing 0.20% Trp (Table 1). The temperature of the house was not allowed to fall below 26.7 C. The experiment was conducted in December and January, and temperature seldom reached 29.4 C. The temperature was controlled to achieve uniform feed intake at a level that a Trp deficiency could be produced. Eight experimental diets were fed (Table 1). The control diet contained 0.20% Trp and levels of other AA were known to support maximum performance (Harms and Russell, 1996). A second diet was used that contained 0.18% Trp and AA levels that were expected to support maximum egg production (EP). Six other diets were formulated to supply 0.12, 0.13, 0.14, 0.15, 0.16, and 0.17% Trp. The other AA were not reduced when the Trp was reduced from 0.18 to 0.17%. The other five diets were formulated in a similar manner. This formulation resulted in the other AA being higher than required and Trp being first limiting. The AA analysis of diets was based on analysis of corn and soybean meal. Tryptophan analysis was made according to the procedure described by Jensen et al. (1990). Eight replicates of five hens were fed each diet. Egg production was recorded for individual hens but was analyzed on a replicate basis. Feed consumption was
INTRODUCTION As soybean meal is replaced with corn in the diet, Met becomes limiting and can be supplied by synthetic Met (Harms and Waldroup, 1963). When more soybean meal is replaced with corn, Lys becomes limiting (Harms and Waldroup, 1963). However, Lys HCl is not routinely used because we do not have a good estimate for the Trp requirement, which is the next limiting amino acid (AA). In most of the previous research, a variety of ingredients were used to provide a diet deficient in Trp. Morris and Wethli (1978) and Wethli and Morris (1978) used a diet containing maize gluten meal, herring meal, starch, gelatin, and cerelose. The diet Jensen et al. (1990) used contained corn gluten meal, meat and bone meal, and poultry by-product meal. More recently Russell and Harms (1999) used a corn-soybean meal diet containing 2% gelatin. Bray (1969) used a basal diet with 8.5% protein and 60% of the protein from corn and 40% from soybean meal. The present experiment was conducted with a cornsoybean meal diet supplemented with AA sufficient to obtain maximum performance.
MATERIALS AND METHODS Hy-Line W36威3 hens, grown in a dark-out house with pine shavings used as litter, were used. The feed during
Received for publication June 30, 1999. Accepted for publication January 28, 2000. 1 Florida Agricultural Experiment Station Journal Series Number R06950. 2 To whom correspondence should be addressed: Harms@dps. ufl.edu. 3 Hy-Line International, West Des Moines, IA 50265.
Abbreviation Key: AA = amino acids; EC = egg content; EP = egg production; EW = egg weight.
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2000 Poultry Science 79:740–742
741
TRYPTOPHAN REQUIREMENT OF COMMERCIAL LAYERSRESEARCH NOTE
RESULTS AND DISCUSSION Egg production increased from 66.2% with hens receiving the diet containing 0.12% Trp to 92.7% when the diet
contained 0.17% Trp (Table 2). The EP from hens receiving the diet with 0.17% Trp was equal to the EP of hens receiving the practical diet with 0.20% Trp. Broken-line regression [y = 92.24 + 0.4352(x − 139.8); R2 = 0.95] of EP on Trp intake resulted in a Trp requirement of 139.8 ± 1.9 mg/hen per d. Egg weight increased from 49.7 g when the diet contained 0.12% Trp to 54.8 g when the diet contained 0.20% Trp (Table 2). However, increase of the level of Trp above 0.18% did not increase EW significantly. Broken-line regression [y = 55.01 + 0.0474 (x − 185.6); R2 = 0.73] of EW on Trp intake resulted in a Trp requirement of 185.6 ± 11.42 mg/hen per d. The finding that EW increased as dietary Trp increased does not agree with previous reports (Ohtani et al., 1989; Jensen et al., 1990; Russell and Harms, 1999). In previous studies, a basal diet was used, and graded levels of Trp were added to the basal. In the present study, the level of Trp was obtained by varying the level of protein and adding other AA to furnish levels that resulted in Trp being the first limiting. The increase in egg content (Table 2) followed the same trend as EP and EW when Trp was increased. However, the increase from increasing the Trp level was 51% for EC, 11% for EW, and 39% for EP. Broken-line regression [y = 45.45+ 0.2203 (x − 149.0); R2 = 0.96] of EC on Trp intake indicated a requirement of 149.0 ± 1.9 mg/hen per d. Feed consumption increased as the level of Trp increased (Table 2). This increase was a result of an increased energy requirement as the output of EC increased.
TABLE 1. Composition of diets Trp content (%) Ingredients
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.20
(%) Yellow corn Soybean meal (48%) Limestone Dicalcium phosphate1 Vitamin mix2 Mineral mix3 Salt DL-Methionine Lysine-HCl Arginine Threonine Valine Isoleucine Calculated analysis (%)4 Protein Methionine Lysine Threonine Valine Isoleucine Arginine Kcal ME/kg 1
78.730 10.700 7.872 1.423 0.250 0.250 0.326 0.042 0.179 0.096 0.050 0.043 0.039 11.26 0.24 0.62 0.44 0.56 0.46 0.73 2,916
77.125 12.312 7.879 1.393 0.250 0.250 0.326 0.056 0.175 0.098 0.056 0.042 0.038 11.90 0.26 0.66 0.47 0.59 0.49 0.78 2,901
75.520 13.925 7.892 1.363 0.250 0.250 0.326 0.069 0.172 0.099 0.062 0.041 0.037 12.53 0.28 0.70 0.50 0.62 0.52 0.83 2,888
73.915 15.537 7.892 1.334 0.250 0.250 0.327 0.082 0.169 0.101 0.069 0.040 0.035 13.17 0.30 0.74 0.53 0.65 0.55 0.88 2,874
72.311 17.149 7.898 1.304 0.250 0.250 0.327 0.095 0.166 0.102 0.075 0.039 0.033 13.80 0.32 0.78 0.56 0.68 0.58 0.93 2,860
70.706 18.761 7.905 1.274 0.250 0.250 0.327 0.108 0.162 0.104 0.081 0.039 0.033 14.44 0.34 0.82 0.59 0.71 0.61 0.98 2,846
69.478 20.341 7.914 1.240 0.250 0.250 0.326 0.101 0.108 ... ... ... ... 14.70 0.34 0.82 0.54 0.70 0.61 0.93 2,831
66.356 23.567 7.928 1.179 0.250 0.250 0.326 0.143 ... ... ... ... ... 15.88 0.40 0.82 0.58 0.77 0.67 1.02 2,803
Contains 18.5% P and 21% Ca. Supplies per kilogram of diet: biotin, 0.2 mg; cholecalciferol, 2,200 IU; choline, 500 mg; ethoxyquin, 65 mg; folic acid, 1 mg; niacin, 60 mg; pantothenic acid, 15 mg; pyridoxine, 5 mg; riboflavin, 5 mg; thiamin, 3 mg; vitamin A, 8,000 IU; vitamin B12, 0.02 mg; vitamin E, 20 IU; and vitamin K, 2 mg. 3 Supplies per kilogram of diet: copper, 10 mg; ethoxyquin, 65 mg; iodine, 2 mg; iron, 60 mg; manganese, 90 mg; selenium, 0.2 mg; zinc, 80 mg. 4 Based on analysis of corn and soybean meal. 2
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measured biweekly, and feed was replaced with fresh feed at that time. One egg from each hen that was laid on the last 2 d of each wk was weighed. Then those eggs were broken out; the shells were washed, allowed to dry, and weighed. Egg mass was calculated by multiplying percentage EP by egg weight (EW) for each replicate. Egg content (EC) was calculated by multiplying EP by EW minus shell weight. The hens were individually weighed at the beginning and end of the experiment, and weight gain was calculated. The daily intake of Trp and energy was calculated by multiplying the amount in the feed by feed consumption. The kilocalories of energy and milligrams of Trp per gram of EC was calculated by dividing the daily intake of energy and Trp by daily EC. The experiment was started at 28 wk of age and continued until 8 wk. However, the first 2 wk were considered as a depletion period and Weeks 3 to 8 were used to test experimental treatments. We use this procedure in our laboratory (Russell and Harms, 1999). The data were subjected to ANOVA with the general linear model procedure of SAS (1988). Duncan’s multiplerange test (1955) was used to determine significant differences among treatment means. The hen requirement for Trp for EP, EC, and BW change was determined by using broken-line regression as described by Noll and Waibel (1989).
742
HARMS AND RUSSELL TABLE 2. Performance of commercial laying hens receiving diets with various levels of Trp Egg content (EC)
Dietary Trp
Egg production
Egg weight
(%) 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.20
(%) 66.2e 75.0d 83.6c 88.1b 89.5ab 92.7a 92.7a 92.3a
(g)
(g)
49.7e 51.6e 52.0de 52.0de 52.8cd 53.6bc 54.0ab 54.8a
29.9e 35.1d 39.4c 41.5b 42.9b 45.1a 45.2a 45.2a
Trp Intake Feed consumption
Energy intake
BW Change
Daily
(g/h/d)
(g)
(mg/h/d)
(mg)
kcal
kcal
68.0d 75.2c 84.9b 88.7ab 88.7ab 89.6ab 92.6a 90.8a
−192d −123c −16b 52.3a 67.3a 71.9a 98.1a 83.9a
81.4g 97.8b 118.9e 133.0d 142.0c 157.5b 161.4b 181.7a
2.74e 2.80e 3.07d 3.20c 3.31c 3.49b 3.57b 3.94a
197d 218c 245b 255ab 254ab 264a 254ab 255ab
6.67a 6.24b 6.22b 6.14bc 5.91cd 5.85d 5.62e 5.52e
g/EC
h/d
g/EC
a–e
Means within a column with a different superscript differ significantly.
ACKNOWLEDGMENT Financial support from Novus International Inc., St. Louis, MO 63304, is gratefully acknowledged.
REFERENCES Bray, D. J., 1969. Studies with corn-soy laying diets. 8. Requirements for limiting amino acids—the basal diet and the requirements for isoleucine, lysine, and tryptophan. Poultry Sci. 48:674–684. Coon, G., and B. Zhang, 1999. Ideal amino acid profile for layers examined. Feedstuffs 71(14):13–15, 31. Duncan, D. B., 1955. Multiple range and multiple F test. Biometrics 11:1–42. Harms, R. H., and C. R. Douglas, 1984. Amino acids, mineral needs for replacement pullets modified. Feedstuffs 56(26):16–17. Harms, R. H., and G. B. Russell, 1996. A re-evaluation of the methionine requirement of the commercial layer. J. Appl. Anim. Res. 9:141–151. Harms, R. H., G. B. Russell, H. Harlow, and F. J. Ivey, 1997. Performance of laying hens fed three levels of methionine in diets containing two levels of protein and energy. J. Appl. Poult. Res. 7:45–52. Harms, R. H., and P. W. Waldroup, 1963. Methionine hydroxy analogue and lysine supplementation of low-protein laying diets. Br. Poult. Sci. 4:267–273. Jensen, L. S., V. M. Calderon, and C. X. Mendonca, Jr., 1990. Response to tryptophan of laying hens fed practical diets varying in protein concentration. Poultry Sci. 69:1956–1965. Morris, T. R., and E. Wethli, 1978. The tryptophan requirement of young laying pullets. Br. Poult. Sci. 19:455–466. Noll, S. L., and P. E. Waibel, 1989. Lysine requirement of the growing turkey in various temperature environments. Poultry Sci. 68:781–794. Ohtani, H., S. Saitoh, H. Ohkawara, Y. Akiba, K. Takahashi, M. Horiguchi, and K. Goto, 1989. Research note: Production performance of laying hens fed L-tryptophan. Poultry Sci. 68:323–326. Russell, G. B., and R. H. Harms, 1999. Tryptophan requirement of the commercial laying hens. Poultry Sci. 78:1283–1285. SAS Institute, 1988. SAS威 User’s Guide: Statistics. SAS Institute Inc., Cary, NC. Wethli, E., and T. R. Morris, 1978. Effects of age on the tryptophan requirement of laying hens. Br. Poult. Sci. 19:559–565.
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The energy consumed per gram of EC decreased from 6.67 kcal when the diet contained 0.12% Trp to 5.52 kcal when the diet contained 0.20% Trp. There was no significant difference in the amount of energy consumed per gram of EC when the diets contained 0.18 or 0.20% Trp. The decrease in energy required to produce a gram of EC became progressively less as the level of Trp increased. This finding agrees with the relationship of energy consumed as EC increased when the level of Met was increased in the diet (Harms et al., 1997). Body weight change was not significantly different among hens that received diets containing 0.15 to 0.20% Trp (Table 2). Reduction of Trp from 0.15 to 0.14% resulted in a significant difference in BW change. Further significant reductions in BW occurred when Trp was reduced to 0.13 or 0.12%. The daily Trp intake increased each time the Trp was increased. This result was largely due to the increase in Trp content in the diet. However, a portion of the increase resulted from an increase in feed intake as the Trp content of the diet increased. The Trp intake per gram of EC increased as the Trp content of the diet increased (Table 2). It has been reported that the Met intake per gram of EC increases as the daily output of EC increases (Harms et al., 1997). An average of 3.67 mg of Trp was required per gram EC for hens consuming the diets with the three highest levels of AA.