J. Anim. Sci. 2002. 80:2646-2655
© 2002 American Society of Animal Science
The tryptophan requirement of nursery pigs1,2
A. C. Guzik*,
L. L. Southern*,3,
T. D. Bidner* and
B. J. Kerr
* Department of Animal Science, Louisiana State University Agricultural Center, Baton Rouge 70803 and
and
USDA-ARS-SOMMRU, National Swine Research & Information Center, 2150 Pammel Drive, Room 2202, Ames, IA 50011
3 Correspondence:
lsouthern{at}agctr.lsu.edu.
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Abstract
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Five experiments were conducted to determine the true digestible Trp (dTrp) requirement of nursery pigs. Treatments were replicated with four or five pens of five or six pigs each. Pigs were weaned at 21 (Exp. 1, 2, and 5) or 19 d (Exp. 3 and 4), and fed common diets for various times and then experimental diets for 8 (Exp. 1), 13 (Exp. 2 and 3), or 14 d (Exp. 4 and 5). Experiment 1 (160 pigs, initial and final BW of 8.4 and 11.4 kg) evaluated six protein sources low in Trp relative to a positive control diet to identify the protein source to be used in subsequent experiments. The results indicated that a diet with Canadian field peas (CFP) supplemented with Trp resulted in ADG, ADFI, and gain:feed (GF) equal to (P > 0.10) the positive control diet. In Exp. 2, 75 pigs (initial and final BW of 13.2 and 19.2 kg) were fed 1) Trp-deficient diet (0.13% dTrp) with CFP, 2) Diet 1 with added Trp (0.23% dTrp), or 3) positive control diet (0.22% dTrp). Daily gain, ADFI, and GF were decreased (P < 0.01) in pigs fed Diet 1 compared with pigs fed Diets 2 and 3, but ADG, ADFI, and GF were equal (P > 0.10) in pigs fed Diets 2 and 3. Experiments 3 (180 pigs, initial and final BW of 5.2 and 7.3 kg), 4 (120 pigs, initial and final BW of 6.3 and 10.2 kg), and 5 (144 pigs, initial and final BW of 10.3 and 15.7 kg) were conducted to estimate the dTrp requirement of nursery pigs with diets using CFP as a primary protein source. The diets used in Exp. 3, 4, and 5 contained 1.35, 1.19, or 1.01% dLys, respectively, and other amino acids were provided at 105% the ratio relative to Lys. Response variables were ADG, ADFI, GF, and plasma urea N concentrations, and data were analyzed using the broken-line model. The levels of dTrp in the diets for Exp. 3 (Phase I, 5.2 to 7.3 kg) were 0.14, 0.17, 0.20, 0.23, 0.26, and 0.29%. The average dTrp requirement was estimated to be 0.21% (0.24% total Trp). The levels of dTrp in the diets for Exp. 4 (Phase II, 6.3 to 10.2 kg) were 0.13, 0.16, 0.19, 0.22, 0.25, and 0.28%. The average dTrp requirement was estimated to be 0.20% (0.23% total Trp). The levels of dTrp in the diets for Exp. 5 (Phase III, 10.3 to 15.7 kg) were 0.130, 0.155, 0.180, 0.205, 0.230, and 0.255%. The average dTrp requirement was estimated to be 0.18% (0.22% total Trp). These results indicate that the true dTrp requirement is 0.21, 0.20, and 0.18% for Phase I (5.2 to 7.3 kg), II (6.3 to 10.2 kg), and III (10.3 to 15.7 kg) nursery pigs, respectively.
Key Words: Pigs • Requirements • Tryptophan
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Introduction
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Tryptophan is an essential dietary amino acid that is equally second or third limiting in typical diets for pigs. In diets consisting primarily of corn, it is the first limiting amino acid because of the low Trp content and availability in corn (Baker et al., 1969). The Trp content in the diet is important for optimal growth performance, and reliable requirement estimates are imperative when formulating diets based on the ideal protein concept. The Trp requirement of nursery pigs has been studied with results varying from study to study. Protein levels, various feedstuffs, and Trp digestibility of the feedstuffs may be reasons for this variation. Most of the research conducted thus far has estimated the total Trp requirement. Review of published research indicates that the Trp requirements for 5- to 20-kg nursery pigs range from 0.14 to 0.25% total Trp. Burgoon et al. (1992) and Schutte et al. (1995) were among the first to estimate the true digestible Trp (dTrp) requirement of young pigs. Recent research has estimated dTrp requirements because this estimation may be more accurate because of the variation in digestibility of Trp in feedstuffs.
Although there have been no estimates of the dTrp requirement of nursery pigs that segregate pigs into Phase I, II, and III, which is typical of current feeding systems, the NRC (1998) provides recommendations for the requirement for Trp based on a summary of work from various scientists. The estimates for pigs weighing 3 to 5 kg, 5 to 10 kg, and 10 to 20 kg are 0.24, 0.22, and 0.18% dTrp, respectively (NRC, 1998). With the lack of empirical data, accurate Trp requirement estimates to optimize growth performance through diet formulation are necessary. The objective of this research was to estimate the dTrp requirement of nursery pigs immediately after weaning (Phase I), of pigs from 7 to 21 d postweaning (Phase II), and of pigs from 21 to 35 d postweaning (Phase III).
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Materials and Methods
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General
The experiments were approved by the University Animal Care and Use Committee.
Five experiments were conducted to estimate the dTrp requirement of nursery pigs. Yorkshire, Yorkshire x Landrace, or Yorkshire x Landrace x Duroc pigs from the Louisiana State University Agricultural Center Swine Unit were used in each experiment. They were housed in an environmentally controlled modular building with under-floor flush and hard plastic slotted floors. Pigs and their environment were monitored twice daily. Pigs were provided ad libitum access to feed and water throughout the experiments. Pigs in each experiment were allotted to treatments on the basis of weight, and gender and ancestry were equalized across treatments in a randomized complete block design. Pens contained an approximately equal number of barrows and gilts.
The diets in all experiments met or exceeded the nutrient requirements (with the exception of Trp for experimental purposes) of nursery pigs (NRC, 1998). Amino acids were provided at a minimum of 105% the ratio relative to Lys (NRC, 1998). The Phase I, II, and III diets contained 1.35, 1.19, or 1.01% true digestible Lys. We will refer to Phase I diets as those fed immediately after weaning, Phase II diets as those fed from 7 to 21 d postweaning, and Phase III diets as those fed from 21 to 35 d postweaning. We also will refer to Phase I, II, and III pigs as those pigs fed Phase I, II, and III diets.
In Exp. 1, diet formulations using corn, soybean meal (SBM), corn gluten meal, and feather meal were based on the amino acid values and true ileal digestibility coefficients in NRC (1998). Amino acid values and true digestibility coefficients for Canadian field peas (CFP) and oatmeal were obtained by using the NRC (1998) values for pea seeds and oat groats, respectively. Amino acid values and apparent digestibility coefficients for spray-dried porcine plasma were obtained by using the NRC (1998) values for spray-dried blood plasma. Gelatin was analyzed for amino acids (Table 1
), and all amino acids were assumed to have a true digestibility coefficient of 95%.
In Exp. 2, 3, 4, and 5, all ingredients were analyzed for amino acids and true digestibility coefficients (except for spray-dried porcine plasma) from NRC (1998) were used. Apparent ileal digestibility coefficients were used for spray-dried porcine plasma (NRC, 1998), and a digestibility coefficient of 95% was used for gelatin. The amino acid composition of the ingredients (Table 1
) was determined after acid hydrolysis (AOAC, 1990). Total sulfur amino acid content was determined after performic acid oxidation followed by acid hydrolysis (AOAC, 1990). Tryptophan content was determined after alkaline hydrolysis (AOAC, 1990).
Experiment 1
The purpose of this experiment was to evaluate Trp-deficient diets containing various protein sources that, when supplemented with crystalline L-Trp, would result in growth performance similar to that of a positive control diet. The diet with optimal results would be used in subsequent requirement studies. One hundred sixty nursery pigs were allotted to seven dietary treatments: 1) positive control (PC), 2) oatmeal, 3) spray-dried porcine plasma, 4) gelatin, 5) corn gluten meal, 6) CFP, or 7) feather meal as primary protein sources (Table 2). The pigs were weaned at an average age of 21 d, and they were fed a Phase I diet for 7 d before the experiment was initiated. This Phase I diet was formulated to provide 1.6% total Lys and 0.31% total Trp, and it contained 38% corn, 21% SBM, 15% whey, 5% lactose, 5% spray-dried porcine plasma, 8% fish meal, 3,000 ppm Zn as ZnO, and an antibiotic, and it was fortified with vitamins and minerals to exceed the nutrient requirements of 3- to 5-kg pigs (NRC, 1998). The average initial and final BW were 8.4 and 11.4 kg. Each treatment was replicated with four pens of five pigs each. The diets were pelleted and fed for 8 d. Response variables included ADG, ADFI, and gain:feed.
Experiment 2
A preliminary experiment was conducted with 75 pigs weighing 13.2- to 19.2-kg (Phase III) to ensure that a CFP Trp-deficient (0.14%) diet, when supplemented with crystalline L-Trp, would result in growth performance similar to a conventional corn-SBM diet. Pigs were weaned at 21 d of age, and they were fed a Phase I diet for 7 d and a Phase II diet for 14 d before the experiment was initiated. The Phase I diet was the same as that used in Exp. 1. The Phase II diet was formulated to provide 1.5% total Lys and 0.29% total Trp, and it contained 46% corn, 29% SBM, 10% whey, 8% fish meal, 3,000 ppm Zn as ZnO, and an antibiotic, and it was fortified with vitamins and minerals to exceed the nutrient requirements of 5- to 10-kg pigs (NRC, 1998). Pigs were allotted to three dietary treatments derived from the Phase III basal diet described in Table 3 and a "typical" positive control. Each treatment was replicated with five pens of six pigs each. Treatments consisted of 1) CFP negative control (NC), 2) NC + Trp, or 3) corn-SBM PC. The experimental diets were fed for 13 d in meal form. Response variables included ADG, ADFI, and gain:feed.
Experiment 3
One hundred eighty pigs (weaned at 19 d of age) were allotted to six dietary treatments derived from the Phase I basal diet described in Table 3. Pigs had an initial and final BW of 5.2 and 7.3 kg. Each treatment was replicated with five pens of six pigs each. Diets were supplemented with crystalline L-Trp at increments of 0.03% to give six treatments containing 0.14, 0.17, 0.20, 0.23, 0.26, or 0.29% dTrp. The experimental diets were fed in meal form for 13 d. Response variables were ADG, ADFI, gain:feed, and plasma urea N (PUN) concentrations.
Experiment 4
One hundred twenty pigs were allotted to six dietary treatments derived from the Phase II basal diet described in Table 3. The pigs were weaned at 19 d of age and were fed the same Phase I diet used in Exp. 1 for 7 d before the experiment was initiated. Pigs had an initial and final BW of 6.3 and 10.2 kg. Each treatment was replicated with four pens of five pigs each. Diets were supplemented with crystalline L-Trp at 0.03% increments to give six treatments containing 0.13, 0.16, 0.19, 0.22, 0.25, or 0.28% dTrp. The experimental diets were fed in meal form for 14 d. Response variables were ADG, ADFI, gain:feed, and PUN concentrations.
Experiment 5
One hundred forty-four pigs were allotted to six dietary treatments derived from the Phase III basal diet described in Table 3. The pigs were weaned at 21 d of age and were fed the same Phase I and II diets used in Exp. 2 for 7 and 14 d, respectively, before the experiment was initiated. Pigs had an initial and final BW of 10.3 and 15.7 kg. Each treatment was replicated with four pens of six pigs each. Diets were supplemented with crystalline L-Trp at 0.025% increments to give six treatments containing 0.130, 0.155, 0.180, 0.205, 0.230, or 0.255% dTrp. The experimental diets were fed in meal form for 14 d. Response variables were ADG, ADFI, gain:feed, and PUN concentrations.
Blood Sampling
At the termination of Exp. 3, 4, and 5, blood was collected via the anterior vena cava. Pigs had access to feed before bleeding. Blood for each pig was placed in 7-mL tubes (Monoject, Sherwood Medical, St. Louis, MO) containing 17.5 mg of sodium fluoride and 14.0 mg of potassium oxalate. Samples were placed on ice for 2 h before centrifugation at 1,600 x g at 4°C for 20 min. Plasma was collected after centrifugation and samples were frozen until analysis. Plasma was analyzed for PUN concentrations by the methods of Laborde et al. (1995).
Statistical Analysis
In each experiment, data were analyzed by ANOVA as a randomized complete block design using the GLM procedures of SAS (SAS Inst. Inc., Cary, NC). In Exp. 1 and 2, the LSD procedure of SAS was used to determine differences among treatment means. In Exp. 3, 4, and 5, contrasts were used to determine linear and quadratic effects of Trp. The two-slope, broken-line regression model was used for all response variables to obtain an estimate of the dTrp requirement (Robbins, 1986). The pen of pigs served as the experimental unit for all data.
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Results
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Experiment 1 (8.4- to 11.4-kg pigs)
Pigs fed the diet containing CFP had ADG, ADFI, and gain:feed similar (P > 0.10) to those fed the conventional corn-SBM diet (Table 4). Pigs fed diets containing oatmeal, spray-dried porcine plasma, or feather meal as protein sources had reduced (P < 0.10) ADG and ADFI, whereas a gelatin-based diet tended to decrease (P = 0.11) gain:feed. Results from this study suggest that CFP are a quality protein source for nursery pigs. This experiment served as a preliminary study to evaluate various protein sources.
Experiment 2 (13.2- to 19.2-kg pigs)
Pigs fed the CFP-diet supplemented with crystalline L-Trp had growth performance similar (P > 0.10) to those fed the PC diet (Table 5). Pigs fed the CFP-without L-Trp supplementation had consistently reduced (P < 0.01) ADG, ADFI, and gain:feed compared with pigs fed the CFP + Trp or the PC diet. This experiment validated the Trp-deficient CFP diet, and this diet was used in subsequent Trp-requirement studies.
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Table 5. Growth performance of Phase III pigs fed a positive control diet or a diet deficient in Trp or this diet supplemented with Trp, Exp. 2a
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Experiment 3 (5.2- to 7.3-kg pigs)
Overall ADG, ADFI, and gain:feed were increased linearly (P < 0.01) and quadratically (P < 0.04) as the dTrp content increased from 0.14 to 0.29% in Phase I pigs (Table 6). Broken-line analysis estimated the optimum dTrp requirement to be 0.208 and 0.217% for ADG and gain:feed during wk 1 of the experiment. Overall, estimates of dTrp requirement were 0.215, 0.210, and 0.182% for ADG, gain:feed, and PUN concentrations, respectively. The average of these values yields an estimate of 0.21% dTrp (0.24% total Trp) for optimum growth performance of Phase I pigs weighing 5.2 to 7.3 kg.
Experiment 4 (6.3- to 10.2-kg pigs)
Overall ADG, ADFI, and gain:feed were increased linearly (P < 0.01) and quadratically (P < 0.08) as the dTrp content increased from 0.13 to 0.28% in Phase II pigs (Table 7). Broken-line analysis estimated the optimum dTrp requirement to be 0.184, 0.179, 0.207, and 0.215% for overall ADG, ADFI, gain:feed, and PUN concentrations, respectively. The average of these values yields an estimate of 0.20% dTrp (0.23% total Trp) for optimum growth of Phase II pigs weighing 6.3 to 10.2 kg.
Experiment 5 (10.3- to 15.7-kg pigs)
Overall ADG, ADFI, and gain:feed were increased linearly (P < 0.03) and quadratically (P < 0.01) as the dTrp content increased from 0.13 to 0.255% in Phase III pigs (Table 8). Broken-line analysis estimated the optimum dTrp requirement to be 0.18, 0.18, 0.181, and 0.168% for overall ADG, ADFI, gain:feed, and PUN concentrations, respectively. The average of these values yields an estimate of 0.18% dTrp (0.22% total Trp) for optimum growth of Phase III pigs weighing 10.3 to 15.7 kg.
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Discussion
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The purpose of Exp. 1 was to compare various protein sources to a positive control diet. This experiment was conducted after three previous attempts to develop a gelatin-based Trp-deficient diet failed (Table 9). In all three experiments, the gelatin-based diet, when supplemented with L-Trp, failed to give growth performance equal to a positive control. A subsequent experiment with chickens fed protein-deficient or protein-adequate diets was conducted to evaluate the gelatin. Daily gain, ADFI, and gain:feed were decreased in chickens fed gelatin regardless of the protein adequacy of the diet (Table 10). Thus, from these preliminary experiments we concluded that the gelatin we were using did not result in optimum growth performance when added to diets formulated to be nutritionally adequate in all nutrients. Gelatin previously has been used as a protein source in Trp requirement studies. However, these researchers did not compare the gelatin-based diet to a conventional diet to validate it as a suitable Trp-deficient diet (Boomgaardt and Baker, 1973; Zimmerman, 1975; Leibholz, 1981).
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Table 9. Growth performance of pigs fed a gelatin-based tryptophan-deficient diet, the deficient diet with supplemental L-Trp, and a positive control diet
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There has been a lot of variation in Trp requirements for young pigs. This variation may be dependent on many factors apart from the diet itself. These factors include environment, genetics, and weight and age of the pig. Although estimating the requirement of any amino acid should seem straight forward, it is not. It is important that the basal Trp-deficient diet, when supplemented with L-Trp, provides growth performance equal to a conventional positive control diet.
Ball and Bayley (1984) estimated the Trp requirement of 2.5-kg pigs using oxidation of Phe as the response variable. A skim milk-dextrose diet was used. The recovery of CO2 indicated that the total Trp requirement was 0.20%. This estimate is lower than the requirement estimate we obtained (0.24% total Trp) in 5.2- to 7.3-kg pigs.
Burgoon et al. (1992) estimated the dTrp requirement of starting, growing, and finishing pigs. In this experiment, growth and digestion trials were used. A corn, fish meal, and corn gluten meal diet was used, and the requirement of pigs weighing 6 to 16 kg was estimated to be 0.15%, which is substantially lower than that of both the NRC (1998) recommendation and the results we obtained in 6.3- to 10.2-kg pigs.
Han et al. (1993) estimated the apparent ileal digestible Trp requirement of pigs weighing 10 to 20 kg. This weight range is similar to the pigs we used. Broken-line regression resulted in an estimate of 0.14% apparent digestible Trp for 10-kg pigs fed an 18% CP diet.
Boomgaardt and Baker (1973) estimated the requirement of 11-kg pigs to be 0.119% total Trp for pigs fed a corn-gelatin-based diet with 18% CP. Three levels of CP (10, 14, and 18%) were used, and the Trp requirement estimate at each level was 0.071, 0.094, and 0.119%, respectively.
More recently, lower estimates ranging from 0.14 to 0.16% total Trp have also been reported for young pigs (LaRue et al., 1985; Borg et al., 1987; Sato et al., 1987). As indicated previously, these low estimates of the Trp requirement may be due to basal diet composition, Trp availability, or general differences from study to study. As a result, it is difficult to provide a definitive Trp requirement estimate that will optimize growth performance of all young pigs. Factors such as age, weight, and protein content of the diet will affect the estimate. In addition, it is likely that the requirement of a pig 20 yr ago is different from that of a pig produced today based on an increased genetic potential for lean growth.
Based on the results of our experiments with the age, weight, and breed of pigs used, the true dTrp requirement of pigs weighing 5.2 to 7.3 kg (Phase I), 6.3 to 10.2 kg (Phase II), and 10.3 to 15.7 kg (Phase III) pigs is 0.21, 0.20, and 0.18%, respectively.
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Implications
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The true digestible tryptophan requirement of Phase I, II, and III pigs was determined to be 0.21, 0.20, and 0.18%, respectively. When formulating diets for these ages of pigs, the use of these estimates will result in optimal growth performance. These estimates are similar to the recommendations of the National Research Council.
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Footnotes
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1 Approved for publication by the Director of the Louisiana Agric. Exp. Sta. as manuscript publ. no. 2002-11-0108. 
2 Research supported in part with funds and supply of amino acids by Nutri-Quest Inc., Chesterfield, MO 63017.
Received for publication September 14, 2001.
Accepted for publication June 19, 2002.
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Ball, R. O., and H. S. Bayley. 1984. Tryptophan requirement of the 2.5-kg piglet determined by the oxidation of an indicator amino acid. J. Nutr. 114:1741–1746.[Abstract/Free Full Text]
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Abstract
Introduction
