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A. J. M. Jansman, J. Th. M. van Diepen, D. Melchior, The effect of diet composition on tryptophan requirement of young piglets, Journal of Animal Science, Volume 88, Issue 3, March 2010, Pages 1017–1027, https://doi.org/10.2527/jas.2008-1627
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ABSTRACT
The aim of the study was to evaluate the requirement for Trp in relation to diet composition in piglets in the period after weaning (BW range of 9 to 24 kg). Two Trp-deficient [relative to the Dutch (CVB, 1996) and NRC (NRC, 1998) requirement values for piglets of 10 to 20 kg of BW] basal diets were formulated: one based on corn and soybean meal and a second one based on wheat, barley, soybean meal, peas, and whey powder [10.0 g/kg of apparent ileal digestible (AID) Lys; 1.4 g/kg of AID Trp; 1.5 g/kg of standardized ileal digestible (SID) Trp]. Both basal diets were supplemented with 0.3, 0.6, and 0.9 g of L-Trp per kg of diet to obtain diets with 1.7, 2.0, and 2.3 g of AID Trp per kg (1.8, 2.1, and 2.4 g of SID Trp per kg), respectively. Each of the 8 treatments was evaluated in 8 replicates (pens with 8 male or female piglets). Average daily feed intake, ADG, and G:F were measured as response criteria. Over the 28-d experimental period, ADG and G:F were greater for the treatments on the wheat/barley diet compared with those on the corn/soybean meal and were increased by the level of Trp in the diet (P < 0.05). Average daily feed intake was only increased by the level of Trp supplementation (P < 0.05). Increasing the Trp level increased ADFI for the corn/soybean meal diet up to 2.3 g of AID Trp per kg (2.4 g of SID Trp per kg) and up to 2.0 g of AID Trp per kg (2.1 g of SID Trp per kg) in the wheat/barley diet (P < 0.05). For both diet types supplementation of free L-Trp increased the G:F up to 1.7 g of AID Trp per kg (1.8 g of SID Trp per kg). Nonlinear regression analysis of the response curves for ADFI using an exponential model for estimating a requirement value for Trp (defined as the Trp level resulting in 95% of the maximum response) revealed a requirement estimate of 2.3 g of AID Trp per kg for the corn/soybean meal-based diet and 2.1 g of AID Trp per kg for the wheat/barley-based diet, equivalent to 2.4 and 2.2 g of SID Trp per kg of diet, respectively. For ADG, a requirement estimate of 2.1 g of AID Trp per kg for both types of diets was derived, equivalent to 2.2 g of SID Trp per kg of diet. The Trp requirement for young piglets seems to be greater than indicated by some commonly used recommendations and does not seem largely dependent on diet ingredient composition.
INTRODUCTION
Tryptophan is an essential AA for pigs. It is considered as the third or fourth limiting AA in diets for piglets after Lys, Met, and Thr. Tryptophan is required for synthesis of proteins for maintenance purposes and for body protein accretion (skeletal muscles). Moreover, Trp is a precursor for the synthesis of specific metabolically active compounds, such as serotonin and niacin (Sève, 1999; LeFloc'h and Sève, 2007) and is involved in the control of immune and inflammatory responses in pigs (Melchior et al., 2005). To maximize pig performance, dietary Trp needs to be adequate. The Trp supply is dependent on protein level of the diet, its ingredient composition, associated intestinal AA digestibility, and its supply in free form as L-Trp.
The requirement for Trp can be expressed as a required concentration in the diet, taking into account its apparent (AID) or standardized ileal digestibility (SID), or as a proportion of the level of AID or SID Lys. The latter fits to the concept of the existence of an ideal dietary AA profile for pigs in which the requirement of essential AA is expressed relative to the requirement for Lys, the first limiting AA (Fuller et al., 1989; Chung and Baker, 1992). Requirement studies for Trp in pigs often concern dose response experiments in which performance (ADFI, ADG, or N retention in the body) is used as response criterion. The requirement is defined as the dietary concentration of (ileal digestible) Trp resulting in a maximum performance of the pigs, assuming that no other factors have limited performance in the study. Alternatively, estimates can be derived from factorial approaches in which AA requirements are calculated from assumed requirements for maintenance purposes and for body protein accretion (NRC, 1998). The estimates for the requirement of Trp in pigs vary between studies and could be affected by age, breed, and sex of the pigs, environmental conditions, choice of regression model for deriving the requirement value, way of expression of the requirement value (as a gross dietary content or on an AID or SID basis), and choice made concerning the experimental diet (Lys, energy, and AA concentrations). Estimates for the Trp requirement in piglets up to 25 kg of BW vary from 1.6 to 2.3 g of Trp per kg of diet (review, NRC, 1998).
Diet composition for piglets can vary substantially around the world and is affected by availability of feed ingredients, local costs for feedstuffs, and legislation with regard to ingredient use. There is little information on the effect of diet composition on the Trp requirement in piglets. Therefore, the aim of the present study was to evaluate the requirement for Trp in postweaning piglets (BW 9 to 24 kg) using 2 diets differing in ingredient composition.
MATERIALS AND METHODS
The experiment was approved by the Animal Experimental Committee of Wageningen University and Research Centre.
Animals, Housing, and Management
In total 512 piglets [(Great York × Pietrain) × Dalland cross] were used in the study. The animals were housed in pens in groups of 8 in an artificially heated, ventilated, and lighted pig unit. Piglets were fed ad libitum using single-space dry feeders. At the start of the preexperimental period, the piglets were allocated to experimental units based on BW and sex. Body weight was used as a blocking factor (low/high). At the end of the preexperimental period and start of the experimental period (after 7 d), 1 piglet was removed from each pen in such a way that the mean BW per pen within a block was as equal as possible. In batch 1, the mean BW of the piglets per pen was 8.2 ± 0.6 kg (mean ± SD) for the block with light piglets and 10.1 ± 0.8 kg for the block with heavy piglets, whereas in batch 2 the mean BW of the piglets per pen was 8.3 ± 0.5 kg (mean ± SD) for the block with light piglets and 9.7 ± 0.7 kg for the block with heavy piglets. The experimental diets were fed during the experimental period of 28 d. Individual BW at d 0, 14, and 28 of the experimental period and feed consumption per pen over d 0 to 14 and 14 to 28 were measured. From these, ADFI, ADG, and G:F of the piglets were calculated.
Experimental Design
Eight experimental treatments were used in the study using a randomized block design. The study was performed in 2 batches, starting 6 wk apart. In each batch, 4 replicates per treatment were evaluated. Each treatment group consisted of 64 piglets during the experimental period divided over 8 pens with 8 piglets each. Four replicates consisted of females and 4 of males. The experiment consisted of a preexperimental period of 7 d and an experimental period of 28 d. Each of the 2 basal diets, calculated to be Trp deficient and differing in ingredient composition, was supplemented with 0.3, 0.6, or 0.9 g/kg of free L-Trp. For both types of diets the calculated ratio of ileal digestible Trp to ileal digestible Lys ranged from 14.0 to 23.0% (AID basis) and from 14.8 to 23.5% (SID basis). The concentrations of AID Lys, Met plus Cys, and Thr in all diets were calculated to be equal to the requirement of piglets for these AA (CVB, 1996).
Diets and Feeding
A similar diet was fed to all piglets during the pre-experimental period of 7 d. The diet (18.5% CP per kg; 2.0 g of AID Trp per kg), based on corn, wheat, barley, tapioca, soybean meal, peas and corn gluten meal as main ingredients, was formulated to be adequate in all nutrients. Two experimental basal Trp-deficient diets were composed, one based on corn and soybean meal and the second one based on wheat, barley, peas, potato protein and whey powder. The basal Trp-deficient diets (I and V) were supplemented with 0.3, 0.6, and 0.9 g ofL-Trp/kg of diet (Ajinomoto Eurolysine SAS, Paris, France) to formulate diets II to IV and diets VI to VIII, respectively. The diets did not contain an antimicrobial growth promoter. The main ingredients of the experimental diets (tapioca, corn, barley, wheat, wheat middlings, peas, corn gluten meal, potato protein, soybean meal, and whey powder; Table 1) were analyzed for the contents of DM, CP, and AA before diet formulation. The diets were further formulated using data on the chemical composition and nutritional value of feed ingredients according to CVB (2004). The 8 experimental treatments received the respective experimental diets I to VIII.
Item . | Corn/soybean meal . | Wheat/barley . |
---|---|---|
Ingredient | ||
Corn | 67.45 | — |
Wheat | — | 14.02 |
Barley | — | 25.00 |
Tapioca | — | 15.00 |
Soybean meal | 19.27 | 3.79 |
Peas | — | 10.00 |
Potato protein | — | 3.00 |
Whey powder, low lactose | — | 2.50 |
Wheat middlings | — | 5.00 |
Corn gluten meal | 4.69 | 9.69 |
Corn starch | 1.00 | 1.00 |
Cane molasses | 3.00 | 3.00 |
Soybean oil | — | 3.73 |
Limestone | 1.86 | 1.63 |
Monocalcium phosphate·1H2O | 1.50 | 1.32 |
Potassium carbonate | 0.04 | 0.14 |
NaCl | 0.25 | 0.25 |
Premix1 | 0.20 | 0.20 |
L-Lysine HCl | 0.48 | 0.50 |
DL-Methionine | 0.13 | 0.12 |
L-Threonine | 0.13 | 0.11 |
Total | 100.0 | 100.0 |
DM2 | 87.3 | 87.9 |
Ash2 | 5.2 | 6.3 |
CP2 | 18.5 | 18.7 |
Crude fat2 | 3.7 | 5.9 |
Crude fiber2 | 2.0 | 3.7 |
Starch3 | 42.4 | 35.8 |
Sugar3 | 4.1 | 4.8 |
Ca2 | 0.96 | 1.06 |
P2 | 0.65 | 0.62 |
Digestible P3 | 0.37 | 0.37 |
Na2 | 0.11 | 0.15 |
K2 | 0.82 | 0.88 |
Cl2 | 0.35 | 0.48 |
NE,3 kcal/kg | 2,316 | 2,316 |
Apparent ileal digestible Lys3 | 1.004 | 1.004 |
Apparent ileal digestible Met3 | 0.384 | 0.384 |
Apparent ileal digestible Met + Cys3 | 0.604 | 0.604 |
Apparent ileal digestible Thr3 | 0.624 | 0.624 |
Apparent ileal digestible Trp3 | 0.144 | 0.144 |
Apparent ileal digestible Ile3 | 0.604 | 0.594 |
Apparent ileal digestible His3 | 0.374 | 0.304 |
Apparent ileal digestible Leu3 | 1.604 | 1.614 |
Apparent ileal digestible Val3 | 0.654 | 0.674 |
Cu,2 mg/kg | 2.9 | 3.1 |
Zn,2 mg/kg | 9.1 | 9.8 |
Fe,2 mg/kg | 28.4 | 34.6 |
Item . | Corn/soybean meal . | Wheat/barley . |
---|---|---|
Ingredient | ||
Corn | 67.45 | — |
Wheat | — | 14.02 |
Barley | — | 25.00 |
Tapioca | — | 15.00 |
Soybean meal | 19.27 | 3.79 |
Peas | — | 10.00 |
Potato protein | — | 3.00 |
Whey powder, low lactose | — | 2.50 |
Wheat middlings | — | 5.00 |
Corn gluten meal | 4.69 | 9.69 |
Corn starch | 1.00 | 1.00 |
Cane molasses | 3.00 | 3.00 |
Soybean oil | — | 3.73 |
Limestone | 1.86 | 1.63 |
Monocalcium phosphate·1H2O | 1.50 | 1.32 |
Potassium carbonate | 0.04 | 0.14 |
NaCl | 0.25 | 0.25 |
Premix1 | 0.20 | 0.20 |
L-Lysine HCl | 0.48 | 0.50 |
DL-Methionine | 0.13 | 0.12 |
L-Threonine | 0.13 | 0.11 |
Total | 100.0 | 100.0 |
DM2 | 87.3 | 87.9 |
Ash2 | 5.2 | 6.3 |
CP2 | 18.5 | 18.7 |
Crude fat2 | 3.7 | 5.9 |
Crude fiber2 | 2.0 | 3.7 |
Starch3 | 42.4 | 35.8 |
Sugar3 | 4.1 | 4.8 |
Ca2 | 0.96 | 1.06 |
P2 | 0.65 | 0.62 |
Digestible P3 | 0.37 | 0.37 |
Na2 | 0.11 | 0.15 |
K2 | 0.82 | 0.88 |
Cl2 | 0.35 | 0.48 |
NE,3 kcal/kg | 2,316 | 2,316 |
Apparent ileal digestible Lys3 | 1.004 | 1.004 |
Apparent ileal digestible Met3 | 0.384 | 0.384 |
Apparent ileal digestible Met + Cys3 | 0.604 | 0.604 |
Apparent ileal digestible Thr3 | 0.624 | 0.624 |
Apparent ileal digestible Trp3 | 0.144 | 0.144 |
Apparent ileal digestible Ile3 | 0.604 | 0.594 |
Apparent ileal digestible His3 | 0.374 | 0.304 |
Apparent ileal digestible Leu3 | 1.604 | 1.614 |
Apparent ileal digestible Val3 | 0.654 | 0.674 |
Cu,2 mg/kg | 2.9 | 3.1 |
Zn,2 mg/kg | 9.1 | 9.8 |
Fe,2 mg/kg | 28.4 | 34.6 |
1The vitamin-mineral premix supplied per kilogram of feed: 10,000 IU of vitamin A, 2,000 IU of vitamin D3, 20 IU of vitamin E, 1.5 mg of vitamin K, 1.0 mg of vitamin B1, 4 mg of vitamin B2, 15 mg of D-pantothenic acid, 25 mg of niacin, 25 µg of biotin, 20 µg of vitamin B12, 0.2 mg of folic acid, 1.5 mg of vitamin B6, 100 mg of choline chloride, 150 mg of Fe, 20 mg of Cu, 65 mg of Zn, 30 mg of Mn, 0.15 mg of Co, 0.5 mg of I, 0.3 mg of Se, 200 mg of Fx aroma Uni (flavor).
2Analyzed values.
3Calculated values.
4Contents of standardized ileal digestible AA for both respective basal diets calculated according to CVB (2004) were 1.03% for Lys, 0.39% for Met, 0.63 and 0.62% for Met + Cys, 0.67% for Thr, 0.15% for Trp, 0.63% for Ile, 0.39 and 0.32% for His, 1.65% for Leu, and 0.70 and 0.72% for Val.
Item . | Corn/soybean meal . | Wheat/barley . |
---|---|---|
Ingredient | ||
Corn | 67.45 | — |
Wheat | — | 14.02 |
Barley | — | 25.00 |
Tapioca | — | 15.00 |
Soybean meal | 19.27 | 3.79 |
Peas | — | 10.00 |
Potato protein | — | 3.00 |
Whey powder, low lactose | — | 2.50 |
Wheat middlings | — | 5.00 |
Corn gluten meal | 4.69 | 9.69 |
Corn starch | 1.00 | 1.00 |
Cane molasses | 3.00 | 3.00 |
Soybean oil | — | 3.73 |
Limestone | 1.86 | 1.63 |
Monocalcium phosphate·1H2O | 1.50 | 1.32 |
Potassium carbonate | 0.04 | 0.14 |
NaCl | 0.25 | 0.25 |
Premix1 | 0.20 | 0.20 |
L-Lysine HCl | 0.48 | 0.50 |
DL-Methionine | 0.13 | 0.12 |
L-Threonine | 0.13 | 0.11 |
Total | 100.0 | 100.0 |
DM2 | 87.3 | 87.9 |
Ash2 | 5.2 | 6.3 |
CP2 | 18.5 | 18.7 |
Crude fat2 | 3.7 | 5.9 |
Crude fiber2 | 2.0 | 3.7 |
Starch3 | 42.4 | 35.8 |
Sugar3 | 4.1 | 4.8 |
Ca2 | 0.96 | 1.06 |
P2 | 0.65 | 0.62 |
Digestible P3 | 0.37 | 0.37 |
Na2 | 0.11 | 0.15 |
K2 | 0.82 | 0.88 |
Cl2 | 0.35 | 0.48 |
NE,3 kcal/kg | 2,316 | 2,316 |
Apparent ileal digestible Lys3 | 1.004 | 1.004 |
Apparent ileal digestible Met3 | 0.384 | 0.384 |
Apparent ileal digestible Met + Cys3 | 0.604 | 0.604 |
Apparent ileal digestible Thr3 | 0.624 | 0.624 |
Apparent ileal digestible Trp3 | 0.144 | 0.144 |
Apparent ileal digestible Ile3 | 0.604 | 0.594 |
Apparent ileal digestible His3 | 0.374 | 0.304 |
Apparent ileal digestible Leu3 | 1.604 | 1.614 |
Apparent ileal digestible Val3 | 0.654 | 0.674 |
Cu,2 mg/kg | 2.9 | 3.1 |
Zn,2 mg/kg | 9.1 | 9.8 |
Fe,2 mg/kg | 28.4 | 34.6 |
Item . | Corn/soybean meal . | Wheat/barley . |
---|---|---|
Ingredient | ||
Corn | 67.45 | — |
Wheat | — | 14.02 |
Barley | — | 25.00 |
Tapioca | — | 15.00 |
Soybean meal | 19.27 | 3.79 |
Peas | — | 10.00 |
Potato protein | — | 3.00 |
Whey powder, low lactose | — | 2.50 |
Wheat middlings | — | 5.00 |
Corn gluten meal | 4.69 | 9.69 |
Corn starch | 1.00 | 1.00 |
Cane molasses | 3.00 | 3.00 |
Soybean oil | — | 3.73 |
Limestone | 1.86 | 1.63 |
Monocalcium phosphate·1H2O | 1.50 | 1.32 |
Potassium carbonate | 0.04 | 0.14 |
NaCl | 0.25 | 0.25 |
Premix1 | 0.20 | 0.20 |
L-Lysine HCl | 0.48 | 0.50 |
DL-Methionine | 0.13 | 0.12 |
L-Threonine | 0.13 | 0.11 |
Total | 100.0 | 100.0 |
DM2 | 87.3 | 87.9 |
Ash2 | 5.2 | 6.3 |
CP2 | 18.5 | 18.7 |
Crude fat2 | 3.7 | 5.9 |
Crude fiber2 | 2.0 | 3.7 |
Starch3 | 42.4 | 35.8 |
Sugar3 | 4.1 | 4.8 |
Ca2 | 0.96 | 1.06 |
P2 | 0.65 | 0.62 |
Digestible P3 | 0.37 | 0.37 |
Na2 | 0.11 | 0.15 |
K2 | 0.82 | 0.88 |
Cl2 | 0.35 | 0.48 |
NE,3 kcal/kg | 2,316 | 2,316 |
Apparent ileal digestible Lys3 | 1.004 | 1.004 |
Apparent ileal digestible Met3 | 0.384 | 0.384 |
Apparent ileal digestible Met + Cys3 | 0.604 | 0.604 |
Apparent ileal digestible Thr3 | 0.624 | 0.624 |
Apparent ileal digestible Trp3 | 0.144 | 0.144 |
Apparent ileal digestible Ile3 | 0.604 | 0.594 |
Apparent ileal digestible His3 | 0.374 | 0.304 |
Apparent ileal digestible Leu3 | 1.604 | 1.614 |
Apparent ileal digestible Val3 | 0.654 | 0.674 |
Cu,2 mg/kg | 2.9 | 3.1 |
Zn,2 mg/kg | 9.1 | 9.8 |
Fe,2 mg/kg | 28.4 | 34.6 |
1The vitamin-mineral premix supplied per kilogram of feed: 10,000 IU of vitamin A, 2,000 IU of vitamin D3, 20 IU of vitamin E, 1.5 mg of vitamin K, 1.0 mg of vitamin B1, 4 mg of vitamin B2, 15 mg of D-pantothenic acid, 25 mg of niacin, 25 µg of biotin, 20 µg of vitamin B12, 0.2 mg of folic acid, 1.5 mg of vitamin B6, 100 mg of choline chloride, 150 mg of Fe, 20 mg of Cu, 65 mg of Zn, 30 mg of Mn, 0.15 mg of Co, 0.5 mg of I, 0.3 mg of Se, 200 mg of Fx aroma Uni (flavor).
2Analyzed values.
3Calculated values.
4Contents of standardized ileal digestible AA for both respective basal diets calculated according to CVB (2004) were 1.03% for Lys, 0.39% for Met, 0.63 and 0.62% for Met + Cys, 0.67% for Thr, 0.15% for Trp, 0.63% for Ile, 0.39 and 0.32% for His, 1.65% for Leu, and 0.70 and 0.72% for Val.
The basal ingredients per type of diet were mixed as 1 batch. Next, the experimental diets were prepared by adding the required amount of free L-Trp, and mixed. The diets were pelleted with addition of steam (pellet diameter 4 mm). Diets were produced by Arkervaart-Twente (Nijkerk, the Netherlands). The diets were fed ad libitum. The animals had free access to water via an automatic drinking device. All experimental diets were analyzed for contents of DM, ash, and CP according to AOAC (1990) and AA using HPLC analysis. Analysis of AA in feed ingredients and diets was performed by Ajinomoto Eurolysine SAS using a JLC-500/V AminoTac AA Analyzer (Jeol, Croissy-sur-Seine, France) after hydrolysis with 6 N HCl at 110°C for 23 h under reflux. The Met and Cys contents in diets were determined after performic oxidation before hydrolysis. The Trp content in diets was determined after hydrolysis at 120°C for 16 h with barium hydroxide and separation by reverse-phase HPLC and fluorometric detection.
The basal diets were also analyzed on the contents of crude fiber (method 978.10; AOAC, 1990), crude fat (method 920.39; AOAC, 1990), and Ca and P (NPR 6425:1995 NL Atomic emission spectrometry–General guidelines). The analyzed nutrient composition of the diets is given in Tables 1 and 2.
Item . | I . | II . | III . | IV . | V . | VI . | VII . | VIII . |
---|---|---|---|---|---|---|---|---|
DM | 87.3 | 87.2 | 87.1 | 87.3 | 87.9 | 87.9 | 88.1 | 88.0 |
CP | 18.5 | 18.2 | 18.0 | 18.5 | 18.7 | 19.0 | 19.1 | 18.9 |
Lys | 1.13 | 1.11 | 1.12 | 1.12 | 1.11 | 1.11 | 1.11 | 1.13 |
Thr | 0.76 | 0.76 | 0.77 | 0.76 | 0.75 | 0.76 | 0.76 | 0.76 |
Met | 0.38 | 0.38 | 0.38 | 0.38 | 0.39 | 0.38 | 0.39 | 0.39 |
Cys | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.29 | 0.29 |
Trp | 0.18 | 0.20 | 0.23 | 0.26 | 0.19 | 0.21 | 0.24 | 0.26 |
Ile | 0.70 | 0.71 | 0.71 | 0.71 | 0.72 | 0.74 | 0.72 | 0.72 |
Leu | 1.81 | 1.84 | 1.84 | 1.84 | 1.85 | 1.86 | 1.86 | 1.87 |
Val | 0.80 | 0.81 | 0.82 | 0.82 | 0.84 | 0.87 | 0.85 | 0.85 |
Arg | 0.94 | 0.94 | 0.93 | 0.94 | 0.82 | 0.83 | 0.82 | 0.82 |
His | 0.43 | 0.44 | 0.43 | 0.44 | 0.37 | 0.37 | 0.37 | 0.37 |
Phe | 0.88 | 0.89 | 0.89 | 0.88 | 0.90 | 0.94 | 0.93 | 0.92 |
Tyr | 0.67 | 0.69 | 0.70 | 0.67 | 0.69 | 0.72 | 0.72 | 0.71 |
Free L-Trp | 0.000 | 0.025 | 0.052 | 0.077 | 0.000 | 0.025 | 0.052 | 0.080 |
Item . | I . | II . | III . | IV . | V . | VI . | VII . | VIII . |
---|---|---|---|---|---|---|---|---|
DM | 87.3 | 87.2 | 87.1 | 87.3 | 87.9 | 87.9 | 88.1 | 88.0 |
CP | 18.5 | 18.2 | 18.0 | 18.5 | 18.7 | 19.0 | 19.1 | 18.9 |
Lys | 1.13 | 1.11 | 1.12 | 1.12 | 1.11 | 1.11 | 1.11 | 1.13 |
Thr | 0.76 | 0.76 | 0.77 | 0.76 | 0.75 | 0.76 | 0.76 | 0.76 |
Met | 0.38 | 0.38 | 0.38 | 0.38 | 0.39 | 0.38 | 0.39 | 0.39 |
Cys | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.29 | 0.29 |
Trp | 0.18 | 0.20 | 0.23 | 0.26 | 0.19 | 0.21 | 0.24 | 0.26 |
Ile | 0.70 | 0.71 | 0.71 | 0.71 | 0.72 | 0.74 | 0.72 | 0.72 |
Leu | 1.81 | 1.84 | 1.84 | 1.84 | 1.85 | 1.86 | 1.86 | 1.87 |
Val | 0.80 | 0.81 | 0.82 | 0.82 | 0.84 | 0.87 | 0.85 | 0.85 |
Arg | 0.94 | 0.94 | 0.93 | 0.94 | 0.82 | 0.83 | 0.82 | 0.82 |
His | 0.43 | 0.44 | 0.43 | 0.44 | 0.37 | 0.37 | 0.37 | 0.37 |
Phe | 0.88 | 0.89 | 0.89 | 0.88 | 0.90 | 0.94 | 0.93 | 0.92 |
Tyr | 0.67 | 0.69 | 0.70 | 0.67 | 0.69 | 0.72 | 0.72 | 0.71 |
Free L-Trp | 0.000 | 0.025 | 0.052 | 0.077 | 0.000 | 0.025 | 0.052 | 0.080 |
1Amino acid composition analyzed by Ajinomoto Eurolysine S.A.S. (Paris, France).
2I–VIII represent the 8 respective experimental diets, with diets I–IV being based on corn/soybean meal and diets V–VIII being based on wheat/barley.
Item . | I . | II . | III . | IV . | V . | VI . | VII . | VIII . |
---|---|---|---|---|---|---|---|---|
DM | 87.3 | 87.2 | 87.1 | 87.3 | 87.9 | 87.9 | 88.1 | 88.0 |
CP | 18.5 | 18.2 | 18.0 | 18.5 | 18.7 | 19.0 | 19.1 | 18.9 |
Lys | 1.13 | 1.11 | 1.12 | 1.12 | 1.11 | 1.11 | 1.11 | 1.13 |
Thr | 0.76 | 0.76 | 0.77 | 0.76 | 0.75 | 0.76 | 0.76 | 0.76 |
Met | 0.38 | 0.38 | 0.38 | 0.38 | 0.39 | 0.38 | 0.39 | 0.39 |
Cys | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.29 | 0.29 |
Trp | 0.18 | 0.20 | 0.23 | 0.26 | 0.19 | 0.21 | 0.24 | 0.26 |
Ile | 0.70 | 0.71 | 0.71 | 0.71 | 0.72 | 0.74 | 0.72 | 0.72 |
Leu | 1.81 | 1.84 | 1.84 | 1.84 | 1.85 | 1.86 | 1.86 | 1.87 |
Val | 0.80 | 0.81 | 0.82 | 0.82 | 0.84 | 0.87 | 0.85 | 0.85 |
Arg | 0.94 | 0.94 | 0.93 | 0.94 | 0.82 | 0.83 | 0.82 | 0.82 |
His | 0.43 | 0.44 | 0.43 | 0.44 | 0.37 | 0.37 | 0.37 | 0.37 |
Phe | 0.88 | 0.89 | 0.89 | 0.88 | 0.90 | 0.94 | 0.93 | 0.92 |
Tyr | 0.67 | 0.69 | 0.70 | 0.67 | 0.69 | 0.72 | 0.72 | 0.71 |
Free L-Trp | 0.000 | 0.025 | 0.052 | 0.077 | 0.000 | 0.025 | 0.052 | 0.080 |
Item . | I . | II . | III . | IV . | V . | VI . | VII . | VIII . |
---|---|---|---|---|---|---|---|---|
DM | 87.3 | 87.2 | 87.1 | 87.3 | 87.9 | 87.9 | 88.1 | 88.0 |
CP | 18.5 | 18.2 | 18.0 | 18.5 | 18.7 | 19.0 | 19.1 | 18.9 |
Lys | 1.13 | 1.11 | 1.12 | 1.12 | 1.11 | 1.11 | 1.11 | 1.13 |
Thr | 0.76 | 0.76 | 0.77 | 0.76 | 0.75 | 0.76 | 0.76 | 0.76 |
Met | 0.38 | 0.38 | 0.38 | 0.38 | 0.39 | 0.38 | 0.39 | 0.39 |
Cys | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.29 | 0.29 |
Trp | 0.18 | 0.20 | 0.23 | 0.26 | 0.19 | 0.21 | 0.24 | 0.26 |
Ile | 0.70 | 0.71 | 0.71 | 0.71 | 0.72 | 0.74 | 0.72 | 0.72 |
Leu | 1.81 | 1.84 | 1.84 | 1.84 | 1.85 | 1.86 | 1.86 | 1.87 |
Val | 0.80 | 0.81 | 0.82 | 0.82 | 0.84 | 0.87 | 0.85 | 0.85 |
Arg | 0.94 | 0.94 | 0.93 | 0.94 | 0.82 | 0.83 | 0.82 | 0.82 |
His | 0.43 | 0.44 | 0.43 | 0.44 | 0.37 | 0.37 | 0.37 | 0.37 |
Phe | 0.88 | 0.89 | 0.89 | 0.88 | 0.90 | 0.94 | 0.93 | 0.92 |
Tyr | 0.67 | 0.69 | 0.70 | 0.67 | 0.69 | 0.72 | 0.72 | 0.71 |
Free L-Trp | 0.000 | 0.025 | 0.052 | 0.077 | 0.000 | 0.025 | 0.052 | 0.080 |
1Amino acid composition analyzed by Ajinomoto Eurolysine S.A.S. (Paris, France).
2I–VIII represent the 8 respective experimental diets, with diets I–IV being based on corn/soybean meal and diets V–VIII being based on wheat/barley.
Statistical Analysis
The results for ADFI, ADG, and G:F were statistically analyzed by ANOVA [Genstat 5; Payne et al. (1993)]. The data were analyzed using block [BW class at allocation (low/high) per batch per sex (1 to 8)] and type of diet (1 to 2) and Trp level (1 to 4) and the interaction between type of diet and Trp level as experimental factors in the statistical model. A significant interaction between type of diet and Trp level was not observed for any of the variables. An effect of a factor in the statistical evaluation was considered to be significant when the probability of having no effect was less than 5% (P < 0.05). Differences between mean values per factor were evaluated further using the LSD test (Snedecor and Cochran, 1980). Performance data are presented as least squares mean values resulting from the ANOVA analysis.
To derive requirement values for Trp, nonlinear regression analysis was performed using REML analysis in Genstat 8.11 (Payne et al., 1993) using the d 0 to 28 data for ADFI and ADG using the following model: y = a + b(1 – e−cx), where y is the response variable [ADFI (g), ADG (g)], a, b are parameters related to start and end of the response curve and b is the maximum response of y, c is a parameter related to curvature steepness, and x is the content of supplemented free L-Trp in the diet (g/kg). The requirement value for Trp was calculated from the content of AID Trp in the basal diet plus the value for x for which 95% of the maximum value of the response b was obtained.
RESULTS
The chemical composition of the diets (Tables 1 to 2) was in agreement with the calculated composition. The analyzed contents of Trp in the experimental diets (Table 2) also matched with the expected values.
The results of the performance of the piglets (ADFI, ADG, and G:F) over d 0 to 14, 14 to 28, and 0 to 28 are presented in Tables 3, 4, and 5, respectively. There was no significant (P > 0.05) diet × Trp level interaction for any of the response variables.
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 419 | 262 | 0.623 |
Corn/SBM | 1.7 | 477 | 331 | 0.693 |
Corn/SBM | 2.0 | 493 | 344 | 0.696 |
Corn/SBM | 2.3 | 532 | 365 | 0.686 |
Wheat/barley | 1.4 | 428 | 282 | 0.657 |
Wheat/barley | 1.7 | 509 | 365 | 0.720 |
Wheat/barley | 2.0 | 544 | 403 | 0.739 |
Wheat/barley | 2.3 | 528 | 386 | 0.730 |
Diet | ||||
Corn/SBM | 480a | 325a | 0.675a | |
Wheat/barley | 502b | 359b | 0.712b | |
LSD | 18 | 16 | 0.015 | |
P-value | <0.05 | <0.001 | <0.001 | |
Trp, AID, g/kg | ||||
1.4 | 424a | 272a | 0.640a | |
1.7 | 493b | 348b | 0.707b | |
2.0 | 519c | 373c | 0.718b | |
2.3 | 530c | 376c | 0.708b | |
LSD | 25 | 23 | 0.022 | |
P-value | <0.001 | <0.001 | <0.001 |
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 419 | 262 | 0.623 |
Corn/SBM | 1.7 | 477 | 331 | 0.693 |
Corn/SBM | 2.0 | 493 | 344 | 0.696 |
Corn/SBM | 2.3 | 532 | 365 | 0.686 |
Wheat/barley | 1.4 | 428 | 282 | 0.657 |
Wheat/barley | 1.7 | 509 | 365 | 0.720 |
Wheat/barley | 2.0 | 544 | 403 | 0.739 |
Wheat/barley | 2.3 | 528 | 386 | 0.730 |
Diet | ||||
Corn/SBM | 480a | 325a | 0.675a | |
Wheat/barley | 502b | 359b | 0.712b | |
LSD | 18 | 16 | 0.015 | |
P-value | <0.05 | <0.001 | <0.001 | |
Trp, AID, g/kg | ||||
1.4 | 424a | 272a | 0.640a | |
1.7 | 493b | 348b | 0.707b | |
2.0 | 519c | 373c | 0.718b | |
2.3 | 530c | 376c | 0.708b | |
LSD | 25 | 23 | 0.022 | |
P-value | <0.001 | <0.001 | <0.001 |
a–cValues with a different superscript in the same column within a factor differ at P < 0.05.
1Based on 8 replicates (pens with 8 piglets) per treatment (mean initial BW 9.1 kg).
2AID = apparent ileal digestible.
3Soybean meal.
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 419 | 262 | 0.623 |
Corn/SBM | 1.7 | 477 | 331 | 0.693 |
Corn/SBM | 2.0 | 493 | 344 | 0.696 |
Corn/SBM | 2.3 | 532 | 365 | 0.686 |
Wheat/barley | 1.4 | 428 | 282 | 0.657 |
Wheat/barley | 1.7 | 509 | 365 | 0.720 |
Wheat/barley | 2.0 | 544 | 403 | 0.739 |
Wheat/barley | 2.3 | 528 | 386 | 0.730 |
Diet | ||||
Corn/SBM | 480a | 325a | 0.675a | |
Wheat/barley | 502b | 359b | 0.712b | |
LSD | 18 | 16 | 0.015 | |
P-value | <0.05 | <0.001 | <0.001 | |
Trp, AID, g/kg | ||||
1.4 | 424a | 272a | 0.640a | |
1.7 | 493b | 348b | 0.707b | |
2.0 | 519c | 373c | 0.718b | |
2.3 | 530c | 376c | 0.708b | |
LSD | 25 | 23 | 0.022 | |
P-value | <0.001 | <0.001 | <0.001 |
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 419 | 262 | 0.623 |
Corn/SBM | 1.7 | 477 | 331 | 0.693 |
Corn/SBM | 2.0 | 493 | 344 | 0.696 |
Corn/SBM | 2.3 | 532 | 365 | 0.686 |
Wheat/barley | 1.4 | 428 | 282 | 0.657 |
Wheat/barley | 1.7 | 509 | 365 | 0.720 |
Wheat/barley | 2.0 | 544 | 403 | 0.739 |
Wheat/barley | 2.3 | 528 | 386 | 0.730 |
Diet | ||||
Corn/SBM | 480a | 325a | 0.675a | |
Wheat/barley | 502b | 359b | 0.712b | |
LSD | 18 | 16 | 0.015 | |
P-value | <0.05 | <0.001 | <0.001 | |
Trp, AID, g/kg | ||||
1.4 | 424a | 272a | 0.640a | |
1.7 | 493b | 348b | 0.707b | |
2.0 | 519c | 373c | 0.718b | |
2.3 | 530c | 376c | 0.708b | |
LSD | 25 | 23 | 0.022 | |
P-value | <0.001 | <0.001 | <0.001 |
a–cValues with a different superscript in the same column within a factor differ at P < 0.05.
1Based on 8 replicates (pens with 8 piglets) per treatment (mean initial BW 9.1 kg).
2AID = apparent ileal digestible.
3Soybean meal.
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F,g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 943 | 639 | 0.678 |
Corn/SBM | 1.7 | 1,124 | 746 | 0.665 |
Corn/SBM | 2.0 | 1,168 | 780 | 0.668 |
Corn/SBM | 2.3 | 1,201 | 797 | 0.664 |
Wheat/barley | 1.4 | 925 | 622 | 0.675 |
Wheat/barley | 1.7 | 1,137 | 761 | 0.670 |
Wheat/barley | 2.0 | 1,185 | 779 | 0.658 |
Wheat/barley | 2.3 | 1,189 | 807 | 0.681 |
Diet | ||||
Corn/SBM | 1,109 | 740 | 0.669 | |
Wheat/barley | 1,109 | 742 | 0.671 | |
LSD | 30 | 20 | 0.010 | |
P-value | NS4 | NS | NS | |
Trp, AID, g/kg | ||||
1.4 | 934a | 630a | 0.677 | |
1.7 | 1,131b | 754b | 0.667 | |
2.0 | 1,176c | 779bc | 0.663 | |
2.3 | 1,195c | 802c | 0.672 | |
LSD | 42 | 29 | 0.014 | |
P-value | <0.001 | <0.001 | NS |
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F,g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 943 | 639 | 0.678 |
Corn/SBM | 1.7 | 1,124 | 746 | 0.665 |
Corn/SBM | 2.0 | 1,168 | 780 | 0.668 |
Corn/SBM | 2.3 | 1,201 | 797 | 0.664 |
Wheat/barley | 1.4 | 925 | 622 | 0.675 |
Wheat/barley | 1.7 | 1,137 | 761 | 0.670 |
Wheat/barley | 2.0 | 1,185 | 779 | 0.658 |
Wheat/barley | 2.3 | 1,189 | 807 | 0.681 |
Diet | ||||
Corn/SBM | 1,109 | 740 | 0.669 | |
Wheat/barley | 1,109 | 742 | 0.671 | |
LSD | 30 | 20 | 0.010 | |
P-value | NS4 | NS | NS | |
Trp, AID, g/kg | ||||
1.4 | 934a | 630a | 0.677 | |
1.7 | 1,131b | 754b | 0.667 | |
2.0 | 1,176c | 779bc | 0.663 | |
2.3 | 1,195c | 802c | 0.672 | |
LSD | 42 | 29 | 0.014 | |
P-value | <0.001 | <0.001 | NS |
a–cValues with a different superscript in the same column within a factor differ at P < 0.05.
1Based on 8 replicates (pens with 8 piglets) per treatment (mean initial BW 9.1 kg).
2AID = apparent ileal digestible.
3Soybean meal.
4Nonsignificant, P > 0.05.
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F,g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 943 | 639 | 0.678 |
Corn/SBM | 1.7 | 1,124 | 746 | 0.665 |
Corn/SBM | 2.0 | 1,168 | 780 | 0.668 |
Corn/SBM | 2.3 | 1,201 | 797 | 0.664 |
Wheat/barley | 1.4 | 925 | 622 | 0.675 |
Wheat/barley | 1.7 | 1,137 | 761 | 0.670 |
Wheat/barley | 2.0 | 1,185 | 779 | 0.658 |
Wheat/barley | 2.3 | 1,189 | 807 | 0.681 |
Diet | ||||
Corn/SBM | 1,109 | 740 | 0.669 | |
Wheat/barley | 1,109 | 742 | 0.671 | |
LSD | 30 | 20 | 0.010 | |
P-value | NS4 | NS | NS | |
Trp, AID, g/kg | ||||
1.4 | 934a | 630a | 0.677 | |
1.7 | 1,131b | 754b | 0.667 | |
2.0 | 1,176c | 779bc | 0.663 | |
2.3 | 1,195c | 802c | 0.672 | |
LSD | 42 | 29 | 0.014 | |
P-value | <0.001 | <0.001 | NS |
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F,g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 943 | 639 | 0.678 |
Corn/SBM | 1.7 | 1,124 | 746 | 0.665 |
Corn/SBM | 2.0 | 1,168 | 780 | 0.668 |
Corn/SBM | 2.3 | 1,201 | 797 | 0.664 |
Wheat/barley | 1.4 | 925 | 622 | 0.675 |
Wheat/barley | 1.7 | 1,137 | 761 | 0.670 |
Wheat/barley | 2.0 | 1,185 | 779 | 0.658 |
Wheat/barley | 2.3 | 1,189 | 807 | 0.681 |
Diet | ||||
Corn/SBM | 1,109 | 740 | 0.669 | |
Wheat/barley | 1,109 | 742 | 0.671 | |
LSD | 30 | 20 | 0.010 | |
P-value | NS4 | NS | NS | |
Trp, AID, g/kg | ||||
1.4 | 934a | 630a | 0.677 | |
1.7 | 1,131b | 754b | 0.667 | |
2.0 | 1,176c | 779bc | 0.663 | |
2.3 | 1,195c | 802c | 0.672 | |
LSD | 42 | 29 | 0.014 | |
P-value | <0.001 | <0.001 | NS |
a–cValues with a different superscript in the same column within a factor differ at P < 0.05.
1Based on 8 replicates (pens with 8 piglets) per treatment (mean initial BW 9.1 kg).
2AID = apparent ileal digestible.
3Soybean meal.
4Nonsignificant, P > 0.05.
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 681 | 450 | 0.661 |
Corn/SBM | 1.7 | 801 | 538 | 0.673 |
Corn/SBM | 2.0 | 830 | 562 | 0.677 |
Corn/SBM | 2.3 | 864 | 579 | 0.671 |
Wheat/barley | 1.4 | 677 | 452 | 0.670 |
Wheat/barley | 1.7 | 823 | 563 | 0.686 |
Wheat/barley | 2.0 | 865 | 591 | 0.684 |
Wheat/barley | 2.3 | 859 | 597 | 0.696 |
Diet | ||||
Corn/SBM | 794 | 532a | 0.670a | |
Wheat/barley | 806 | 551b | 0.684b | |
LSD | 21 | 15 | 0.008 | |
P-value | 0.27 | <0.05 | <0.01 | |
Trp, AID, g/kg | ||||
1.4 | 679a | 451a | 0.665a | |
1.7 | 812b | 551b | 0.680b | |
2.0 | 847c | 576c | 0.680b | |
2.3 | 861c | 588c | 0.683b | |
LSD | 30 | 21 | 0.011 | |
P-value | <0.001 | <0.001 | <0.01 |
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 681 | 450 | 0.661 |
Corn/SBM | 1.7 | 801 | 538 | 0.673 |
Corn/SBM | 2.0 | 830 | 562 | 0.677 |
Corn/SBM | 2.3 | 864 | 579 | 0.671 |
Wheat/barley | 1.4 | 677 | 452 | 0.670 |
Wheat/barley | 1.7 | 823 | 563 | 0.686 |
Wheat/barley | 2.0 | 865 | 591 | 0.684 |
Wheat/barley | 2.3 | 859 | 597 | 0.696 |
Diet | ||||
Corn/SBM | 794 | 532a | 0.670a | |
Wheat/barley | 806 | 551b | 0.684b | |
LSD | 21 | 15 | 0.008 | |
P-value | 0.27 | <0.05 | <0.01 | |
Trp, AID, g/kg | ||||
1.4 | 679a | 451a | 0.665a | |
1.7 | 812b | 551b | 0.680b | |
2.0 | 847c | 576c | 0.680b | |
2.3 | 861c | 588c | 0.683b | |
LSD | 30 | 21 | 0.011 | |
P-value | <0.001 | <0.001 | <0.01 |
a–cValues with a different superscript in the same column within a factor differ at P < 0.05.
1Based on 8 replicates (pens with 8 piglets) per treatment (mean initial BW 9.1 kg).
2AID = apparent ileal digestible.
3Soybean meal.
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 681 | 450 | 0.661 |
Corn/SBM | 1.7 | 801 | 538 | 0.673 |
Corn/SBM | 2.0 | 830 | 562 | 0.677 |
Corn/SBM | 2.3 | 864 | 579 | 0.671 |
Wheat/barley | 1.4 | 677 | 452 | 0.670 |
Wheat/barley | 1.7 | 823 | 563 | 0.686 |
Wheat/barley | 2.0 | 865 | 591 | 0.684 |
Wheat/barley | 2.3 | 859 | 597 | 0.696 |
Diet | ||||
Corn/SBM | 794 | 532a | 0.670a | |
Wheat/barley | 806 | 551b | 0.684b | |
LSD | 21 | 15 | 0.008 | |
P-value | 0.27 | <0.05 | <0.01 | |
Trp, AID, g/kg | ||||
1.4 | 679a | 451a | 0.665a | |
1.7 | 812b | 551b | 0.680b | |
2.0 | 847c | 576c | 0.680b | |
2.3 | 861c | 588c | 0.683b | |
LSD | 30 | 21 | 0.011 | |
P-value | <0.001 | <0.001 | <0.01 |
Item . | AID2 Trp, g/kg . | ADFI, g . | ADG, g . | G:F, g/g . |
---|---|---|---|---|
Diet type | ||||
Corn/SBM3 | 1.4 | 681 | 450 | 0.661 |
Corn/SBM | 1.7 | 801 | 538 | 0.673 |
Corn/SBM | 2.0 | 830 | 562 | 0.677 |
Corn/SBM | 2.3 | 864 | 579 | 0.671 |
Wheat/barley | 1.4 | 677 | 452 | 0.670 |
Wheat/barley | 1.7 | 823 | 563 | 0.686 |
Wheat/barley | 2.0 | 865 | 591 | 0.684 |
Wheat/barley | 2.3 | 859 | 597 | 0.696 |
Diet | ||||
Corn/SBM | 794 | 532a | 0.670a | |
Wheat/barley | 806 | 551b | 0.684b | |
LSD | 21 | 15 | 0.008 | |
P-value | 0.27 | <0.05 | <0.01 | |
Trp, AID, g/kg | ||||
1.4 | 679a | 451a | 0.665a | |
1.7 | 812b | 551b | 0.680b | |
2.0 | 847c | 576c | 0.680b | |
2.3 | 861c | 588c | 0.683b | |
LSD | 30 | 21 | 0.011 | |
P-value | <0.001 | <0.001 | <0.01 |
a–cValues with a different superscript in the same column within a factor differ at P < 0.05.
1Based on 8 replicates (pens with 8 piglets) per treatment (mean initial BW 9.1 kg).
2AID = apparent ileal digestible.
3Soybean meal.
During the first 2 wk of the experimental period, ADFI, ADG, and G:F were affected by diet type (greater for the wheat/barley diet compared with corn/soybean meal diet; P = 0.018 for ADFI and P < 0.001 for ADG and G:F) and the level of Trp in the diet (P < 0.001). Average daily feed intake and ADG in this period were greater for wheat/barley treatments compared with the corn/soybean meal diet. Increasing the Trp level increased ADFI for both types of diets (P < 0.001). Gain-to-feed ratio was also greater for the pigs fed the wheat/barley diet compared with the pigs fed the corn/soybean meal diet (P < 0.001) and increased by the level of AID Trp in the diet (P < 0.001). Gain-to-feed ratio was on average greater (P < 0.001) for the treatments on the wheat/barley based diet compared with the treatments on the corn/soybean meal diet. For both types of diet G:F improved with the supplementation of free L-Trp.
During the d 14 to 28 of the experimental period, results for ADFI and ADG were similar in trend compared with the first 2 wk of the experiment with regard to the effect of the Trp level in the diet. The ADFI and ADG increased with L-Trp supplementation for both types of diet (P < 0.001). During this period there was no effect of the type (P > 0.05) of diet (corn/soybean meal vs. wheat/barley) on ADFI and ADG. Gain-to-feed ratio did not differ (P > 0.05) between treatments during this part of the experiment.
For the entire experimental period (0 to 28 d), ADG and G:F were greater for the pigs receiving the wheat/barley diet compared corn/soybean meal diet (P = 0.019 for ADG and P = 0.002 for G:F) and were increased by the level of Trp in the diet (P < 0.001 for ADG and P = 0.008 for G:F). Average daily feed intake was increased by the level of Trp supplementation (P < 0.001). Increasing the Trp level increased ADFI for the corn/soybean diet up to 2.3 g/kg of AID Trp and up to 2.0 g/kg of AID Trp in the wheat/barley diet. Average daily gain was greater for the wheat/barley compared with the corn/soybean meal dietary treatments (P = 0.019; on average 551 vs. 532 g). Increasing the Trp level increased ADG in both types of diets (P < 0.001). Gain-to-feed ratio was greater for the pigs fed the wheat/barley diet compared with the pigs fed the corn/soybean meal diet (P = 0.002). For the pigs receiving the corn/soybean meal diet, G:F did not increase with Trp supplementation. For the pigs receiving the wheat/barley diet, G:F was improved (P < 0.01) for diets with 1.7 and 2.3 g/kg of AID Trp compared with the treatment fed the diet with 1.4 g/kg of AID Trp.
The nonlinear regression analysis of the ADFI and ADG data for both sexes over the entire experimental period against the level of AID Trp in the diet is given in Figures 1 and 2. Because no clear response to L-Trp supplementation on G:F was obtained, regression analysis was not applied using these data. In Table 6 parameter estimates of the nonlinear regression models as well as derived requirement values for AID and SID Trp (based on 95% of the calculated maximum response of Trp supplementation) are given. Estimated requirement values for AID Trp based on data for ADFI were numerically slightly greater for the corn/soybean diet compared with the wheat/barley-based diet in both sexes. For ADG, the estimate for the Trp requirement was the same for both types of diets and both sexes. All requirement estimates were within the range of dietary levels of AID Trp tested in the present study.
Item . | a, g/d . | SE . | b, g/d . | SE . | c . | SE . | Trp req. value,1,2g/kg . | Trp req. value,3,4 g/kg . |
---|---|---|---|---|---|---|---|---|
Males | ||||||||
ADFI, g | ||||||||
Corn/SBM5 | 679 | 49 | 167 | 34 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 167 | 34 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 465 | 34 | 104 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 465 | 34 | 131 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
Gilts | ||||||||
ADFI, g | ||||||||
Corn/SBM | 679 | 49 | 213 | 30 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 213 | 30 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 437 | 39 | 144 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 437 | 39 | 170 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
Item . | a, g/d . | SE . | b, g/d . | SE . | c . | SE . | Trp req. value,1,2g/kg . | Trp req. value,3,4 g/kg . |
---|---|---|---|---|---|---|---|---|
Males | ||||||||
ADFI, g | ||||||||
Corn/SBM5 | 679 | 49 | 167 | 34 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 167 | 34 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 465 | 34 | 104 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 465 | 34 | 131 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
Gilts | ||||||||
ADFI, g | ||||||||
Corn/SBM | 679 | 49 | 213 | 30 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 213 | 30 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 437 | 39 | 144 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 437 | 39 | 170 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
1On an AID basis.
2Based on the content of AID Trp resulting in 95% of the calculated maximum response (b).
3On a SID basis.
4Recalculated from the content of AID Trp resulting in 95% of the calculated maximum response, using 0.14 g/kg as basal ileal endogenous loss for Trp (Jansman et al., 2002).
5SBM = soybean meal.
Item . | a, g/d . | SE . | b, g/d . | SE . | c . | SE . | Trp req. value,1,2g/kg . | Trp req. value,3,4 g/kg . |
---|---|---|---|---|---|---|---|---|
Males | ||||||||
ADFI, g | ||||||||
Corn/SBM5 | 679 | 49 | 167 | 34 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 167 | 34 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 465 | 34 | 104 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 465 | 34 | 131 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
Gilts | ||||||||
ADFI, g | ||||||||
Corn/SBM | 679 | 49 | 213 | 30 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 213 | 30 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 437 | 39 | 144 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 437 | 39 | 170 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
Item . | a, g/d . | SE . | b, g/d . | SE . | c . | SE . | Trp req. value,1,2g/kg . | Trp req. value,3,4 g/kg . |
---|---|---|---|---|---|---|---|---|
Males | ||||||||
ADFI, g | ||||||||
Corn/SBM5 | 679 | 49 | 167 | 34 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 167 | 34 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 465 | 34 | 104 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 465 | 34 | 131 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
Gilts | ||||||||
ADFI, g | ||||||||
Corn/SBM | 679 | 49 | 213 | 30 | 3.30 | 0.18 | 2.31 | 2.45 |
Wheat/barley | 679 | 49 | 213 | 30 | 4.55 | 0.20 | 2.06 | 2.20 |
ADG, g | ||||||||
Corn/SBM | 437 | 39 | 144 | 28 | 4.37 | 0.21 | 2.09 | 2.23 |
Wheat/barley | 437 | 39 | 170 | 26 | 4.37 | 0.21 | 2.09 | 2.23 |
1On an AID basis.
2Based on the content of AID Trp resulting in 95% of the calculated maximum response (b).
3On a SID basis.
4Recalculated from the content of AID Trp resulting in 95% of the calculated maximum response, using 0.14 g/kg as basal ileal endogenous loss for Trp (Jansman et al., 2002).
5SBM = soybean meal.
DISCUSSION
The current study was carried out to evaluate the effects of diet composition on the Trp requirement of young piglets (9 to 24 kg of BW). The diet based on corn, soybean meal, and corn gluten meal can be considered as a diet typical for North and South America. The second diet based on wheat, barley, tapioca, soybean meal, potato protein, peas, whey powder, wheat middlings, and corn gluten meal can be regarded as a diet more typical for Western Europe.
The results of the study over the whole experimental period show that at the same level of free L-Trp supplementation, ADFI and ADG were numerically greater for the wheat/barley-based diet compared with the corn/soybean meal diet, except for the performance of the groups receiving the basal diets and for the ADFI at the greatest amount of supplementation of Trp, for which the intake was almost identical. Overall, ADFI and ADG were greater for the groups fed the wheat/barley-based diets compared with the groups receiving the corn/soybean meal dietary treatments. Also, G:F was greater for the treatments fed the wheat/barley-based diet compared with the corn/soybean meal-based diet. Because both types of diets were formulated to be nutritionally adequate for all nutrients, except for Trp, there is currently no obvious explanation for the difference in response curves between both types of diets. It might be related to differences in ingredients or combinations of ingredients used in the 2 types of diets on the palatability of the diet or due to a difference in actual AID of AA in the ingredients used in the diets compared with the tabulated values used during diet formulation (CVB, 2004).
The relatively large response of ADFI of the piglets toward L-Trp supplementation of both Trp-deficient diets can be related to 2 factors. First, reduced serotonin concentrations in the hypothalamus of pigs were found when feeding Trp-deficient basal diets [knowing that Trp serves as a precursor of serotonin (5-hydroxytryptamine) in the brain (Henry et al., 1996)]. Serotonin is an inhibitory neurotransmitter, synthesized in various tissues and cells, and in the brain involved in feed intake regulation (Henry et al., 1996). Because serotonin is found in the hypothalamus, but is unable to pass the blood-brain barrier, serotonin in the brain needs to be synthesized locally from Trp as precursor. Adeola and Ball (1992) also observed an increased hypothalamic serotonin concentration with an increase in the dietary Trp concentration in pigs of about 90 kg of BW. Henry et al. (1992, 1996) and Sève et al. (1991) reported a positive relationship between the dietary Trp content and Trp blood plasma concentration, the ratio between Trp and large neutral AA (LNAA) in blood plasma, and the concentration of brain serotonin. Second, more recently Zhang et al. (2007) showed that oral administration of increased dietary concentrations of free L-Trp increases the expression and concentration of ghrelin in the gastric fundus and plasma of weanling pigs. Ghrelin is a peptide hormone involved in the regulation of feed intake and in the signaling between the digestive system and the brain. Thus, both factors could be involved in explaining in the relationship between Trp intake and voluntary feed intake in pigs.
The results of the present study show that both basal diets were deficient in Trp (1.4 g of AID Trp per kg). Supplementation of free L-Trp to both diets resulted in an increase in ADFI and ADG, and to a lesser extent in an improvement in G:F. The supplementation of L-Trp to the corn/soybean meal and the wheat/barley based diet resulted in a significant increase in performance (ADFI and ADG) up to 2.0 g of AID Trp per kg. Furthermore, Trp supplementation to a level of 2.3 g of AID Trp in the diet only tended to increase ADFI (except for male piglets fed the wheat/barley-based diet) and ADG (except for male piglets fed the wheat/barley-based diet).
The Trp requirement estimates based on nonlinear regression analysis of the response curves for ADFI showed a requirement value of 2.3 g of AID Trp per kg of diet for the corn/soybean meal-based diet and 2.1 g of AID Trp per kg for the wheat/barley-based diet in both sexes. For ADG, the estimate for the Trp requirement was derived at 2.1 g of AID Trp per kg of diet for both diets and sexes. These requirement values fell within the range of dietary Trp levels evaluated in the present study. These values are greater than recommended by NRC (1998) for piglets of 10 to 20 kg of BW (1.6 g/kg of AID Trp for piglets) and those reported by Han et al. (1993), 1.4 g/kg (AID) in piglets of 10 kg of BW; by Borg et al. (1987), 1.6 g/kg (total quantity in the diet) in piglets of 6 to 10 kg of BW; and by Guzik et al. (2002), 1.8 g/kg of SID Trp in piglets of 10 to 16 kg of BW. Eder et al. (2001) reported estimates of 1.8 to 1.9 g/kg of ileal digestible Trp in young piglets. In growing pigs from 25 to 40 kg of BW, using a Lys-limiting basal diet (0.66% AID Lys), Quant et al. (2007) found an optimal Trp-to-Lys ratio of 15.6% on an AID basis using performance data and plasma urea N as response criteria. Our results are in closer agreement with data of Jansman et al. (2000; 2.0 and 2.3 g/kg of AID Trp) and Schutte et al. (1995; 2.1 g/kg of AID Trp) in piglets in the same BW range as used in the present study. Susenbeth (2006) determined the optimal Trp-to-Lys ratio based on a review of 33 Trp requirement experiments with piglets and growing pigs and defined the requirement value as the smallest Trp-to-Lys ratio (using concentrations in the diets as fed) tested within the plateau phase of the response graph using ADFI and ADG as response criteria. A mean value of 17.4% (SD 2.3%; n = 33) for the optimum Trp-to-Lys ratio was reported. The author did not include data in the survey of studies in which only a linear effect of Trp supplementation on performance was observed, and no plateau value was reached. No absolute value for the dietary requirement of Trp was given, as according to the author, the variation in the Lys concentration of the experimental diets relative to the Lys requirement value was large. Although the author did not find an effect of Lys or protein content of the diet on the optimum Trp-to-Lys ratio, it can be stated that the optimum ratio between Trp and Lys could be affected by the concentration of Lys in the diet. Indeed, experiments designed to set a requirement in ratio to Lys should use diets that are second limiting in Lys (Boisen, 2003; Barea et al., 2009) or at the assumed requirement value for Lys. The concentration of Lys used in the diets of the present study (1.00% AID Lys) was assumed to be at the requirement value according to the Dutch standard (CVB, 1996) and was certainly not above the requirement for Lys according to recent findings of Kendall et al. (2008; 1.30% SID Lys).
There is debate about the suitability of the various models for fitting the response curves in nutrient requirement studies (e.g., Fuller and Garthwaite, 1993; Robbins et al., 2006; Pesti et al., 2009). In the present study, nonlinear regression analysis with an exponential model was used to derive a requirement value for AID Trp in both types of diets. Values for the requirement of AID Trp were calculated at 95% of the maximum response to Trp supplementation. A similar approach for estimating nutrient requirement values using dose-response studies has been used by Mack et al. (1999) and Eder et al. (2001). Also, linear and nonlinear broken line models have been proposed for deriving requirement values from such studies (Robbins et al., 2006). In the latter approach, the requirement value is defined as the smallest value for the independent variable for which the maximum (plateau) value of the dependent variable is reached. It has been mentioned that linear broken-line models could be more suitable for individuals, whereas a curvilinear-plateau model might be more suitable for fitting data derived from a population of animals. In the present study an exponential model was used for deriving requirement values because of the nature of the response curve (diminishing the increment of the response with increasing Trp levels seems to follow general biological responses in groups of animals in which the relative efficiency of nutrient utilization is decreasing with increasing supply), and because of the relatively small number dietary Trp levels tested in the present study, limiting the capacity of the data to estimate a plateau value for the performance of the piglets. Although the number of treatments was limited to 4, which is small for the use of linear-plateau regression analysis (Pesti et al., 2009), analysis of the data presented in the current study over both types of diets and sexes with a linear broken-line model, however, revealed requirement values for ADFI and ADG of 1.80 and 1.79 g of AID Trp per kg, respectively. These values are less than those derived from the use of the exponential model. Recently, Barea et al. (2009) also reported a smaller requirement value for valine in piglets when using a linear broken-line model than when using a curvilinear model for fitting the data.
Different factors can explain the variation in requirement values among studies, such as age and BW of the piglets, breed/genotype, sex, response variable used, and way of expression of results [requirement value expressed as a total (gross) concentration in the diet or as an AA content on AID or SID basis or expressed proportionally to the requirement value for Lys on an AID or SID basis]. In addition, diet (ingredient and nutrient) composition could affect requirement values for AA. Although the overall average performance of the piglets receiving the corn/soybean meal diet was less compared with the wheat/barley-based diet, only the estimated requirement for Trp based on the results for ADFI in the present study was slightly greater for the first diet. Jansman et al. (2000) reported a relationship between the ratio of Trp and LNAA and the Trp requirement. Using a diet with a large Trp:LNAA ratio [0.048 (AID basis) and 170 g of CP/kg in basal diet] the Trp requirement was estimated at 2.3 g of AID Trp per kg, whereas using a diet with a smaller Trp:LNAA ratio [0.034 (AID basis) and 200 g of CP/kg in basal diet] Trp requirement was estimated at 1.9 g of AID Trp per kg. This could suggest a metabolic interaction between Trp and LNAA affecting serotonin concentrations in the brain, which could in turn affect voluntary feed intake as also concluded by Henry et al. (1996). In the present study, both the dietary CP content as well as the Trp:LNAA ratio was similar in both types of basal diets, so this factor did not largely affect the Trp requirement estimates in the present study.
Diet composition could affect AA requirement estimates in the case of Thr, which is relatively largely represented in endogenous protein lost in the digestive system (Jansman et al., 2002). In case basal diets would induce a variable loss of endogenous protein and AA, this could result in differences in AA requirement values. For Thr, for example, a relationship between its requirement value and the dietary fiber concentration could be assumed, related to the induction of greater endogenous protein losses in the gut by high fiber diets (Schulze et al., 1994) and the increase in tissue weight of the intestinal tract when feeding high fiber diets (Jørgensen et al., 1996). In addition, greater oxidative losses of AA may be assumed to be related to the metabolic costs for the synthesis and recycling of endogenous protein (Grala et al., 1997) affecting AA availability for body protein accretion. The contribution of Trp in basal endogenous protein in pigs, however, is relatively small (Jansman et al., 2002), suggesting that this is not an important factor in explaining the results of the present study.
Tryptophan seems to have other specific metabolic functions in dealing with stress responses (Koopmans et al., 2005, 2006) via the effects of Trp on brain serotonin synthesis and turnover (Le Floc'h and Sève, 2007), which could potentially interfere with requirement estimates for this AA. Increased quantity of dietary Trp can reduce aggressive behavior and reduce physiological responses to stress. In addition, Trp has been shown to be involved in the control of immune and inflammatory responses (Le Floc'h et al., 2004; Le Floc'h and Sève, 2007). Tryptophan is a precursor for the formation of kynurenine, the first step of a metabolic pathway for the production of xanthurenic and anthranilic acid and eventually picolinic acid and niacin. Melchior et al. (2004, 2005) showed that this metabolic pathway was involved in Trp metabolism disturbances associated with inflammatory responses. In their studies chronic lung inflammation in piglets reduced plasma free Trp concentrations. Dietary supplementation of free Trp increased Trp concentrations in blood of these pigs. This suggests that Trp requirement is increased under suboptimal health conditions. Also, piglets maintained in poor sanitary conditions were shown to have less plasma Trp concentrations and seem to have a greater Trp requirement (Le Floc'h et al., 2006). The former suggests that health status of pigs could affect their requirement estimate for Trp. In the present study, however, piglets were generally in good health condition in each of the experimental groups, so this could not be considered as an important factor in relation to the estimated requirement value for Trp.
It can be concluded that supplementing low-Trp diets based on corn/soybean meal or on wheat/barley as main ingredients increased piglet performance. Based on the results for ADFI and ADG, the requirement for Trp in young male and female piglets for both diets was estimated at 2.1 g of AID Trp per kg (equivalent to 2.2 g of SID Trp per kg of diet), except for a slightly greater value for the estimated Trp requirement based on the results for ADFI in the corn/soybean meal diet (2.3 g of AID Trp per kg). The Trp requirement for young piglets seems to be greater than indicated by some commonly used recommendations and does not seem to be largely dependent on diet ingredient composition.
LITERATURE CITED
Author notes
The authors thank J. W. van Riel (Animal Sciences Group, Lelystad, the Netherlands) for his support in the statistical analysis of the results of the study.