Determining the effects of standardized ileal digestible tryptophan:lysine ratio and tryptophan source in diets containing dried distillers grains with solubles on growth performance and carcass characteristics of finishing pigs

A total of 2,290 pigs (PIC 1050 Ã— 337; initially 157 lb) were used to determine the effect of tryptophan source (L-tryptophan vs. soybean meal) and increasing SID tryptophan:lysine ratio in diets containing 30% dried distillers grains with solubles (DDGS) on finishing pig performance. Pens of pigs were balanced by initial weight and randomly allotted to 1 of 7 dietary treatments in a completely randomized design with 26 to 28 pigs per pen and 10 to 13 replications per treatment. Treatments were arranged as a 2 Ã— 3 factorial with main effects of tryptophan source (L-tryptophan or soybean meal) and SID tryptophan:lysine ratio (18, 20, and 22% of lysine). The seventh treatment was a negative control diet formulated to a 16% SID tryptophan:lysine ratio.; Swine Day, Manhattan, KS, November 15, 2012


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Determining the Effects of Standardized Ileal Digestible Tryptophan:Lysine Ratio and Tryptophan Source in Diets Containing Dried Distillers Grains with Solubles on Growth Performance and Carcass Characteristics of Finishing Pigs 1 S. Nitikanchana 2 , M. D. Tokach, S. S. Dritz 2 , J.L. Usry 3 , R. D. Goodband, J. M. DeRouchey, and J. L. Nelssen Summary A total of 2,290 pigs (PIC 1050 × 337; initially 157 lb) were used to determine the effect of tryptophan source (L-tryptophan vs. soybean meal) and increasing SID tryptophan:lysine ratio in diets containing 30% dried distillers grains with solubles (DDGS) on finishing pig performance.Pens of pigs were balanced by initial weight and randomly allotted to 1 of 7 dietary treatments in a completely randomized design with 26 to 28 pigs per pen and 10 to 13 replications per treatment.Treatments were arranged as a 2 × 3 factorial with main effects of tryptophan source (L-tryptophan or soybean meal) and SID tryptophan:lysine ratio (18, 20, and 22% of lysine).The seventh treatment was a negative control diet formulated to a 16% SID tryptophan:lysine ratio.
Overall, a tryptophan source × SID tryptophan:lysine ratio interaction (linear, P = 0.03) was observed for F/G.Increasing SID tryptophan:lysine ratio improved (quadratic, P < 0.01) F/G up to 20% when soybean meal was the source of tryptophan, but the optimum was at only 18% when L-tryptophan was added.Increasing the SID tryptophan:lysine ratio increased (linear, P = 0.01) carcass yield when using L-tryptophan; however, the greatest yield was observed (quadratic, P = 0.03) at 18% SID tryptophan:lysine ratio when soybean meal was used, resulting in a tryptophan source × SID tryptophan:lysine ratio interaction (linear, P = 0.01).For the main effect of SID tryptophan:lysine ratio, ADG and F/G improved (quadratic, P < 0.01), with increasing SID tryptophan:lysine ratio demonstrating the best performance when SID tryptrophan was at 20% of lysine.Loin depth was greatest in the control diet (16% SID tryptophan:lysine ratio) and lowest in 18% SID tryptophan:lysine ratio (quadratic, P = 0.02).For the main effect of tryptophan source, no differences were observed in feed intake or feed efficiency among sources of tryptophan; however, we saw a trend (P = 0.07) for greater ADG when soybean meal was the tryptophan source.Backfat was greater (P = 0.04) and percentage lean (P = 0.02) was lower in pigs fed with L-tryptophan than those with soybean meal as the tryptophan source.This study indicated an optimum SID tryptophan:lysine ratio of 20% for 157-to 279-lb pigs.Because using

Introduction
Dried distillers grains with solubles are widely used in swine diets in the United States.Tryptophan is the second limiting amino acid after lysine in diets containing DDGS.A previous study (Barnes et al., 2011 4 ) observed a linear increase in ADG and ADFI as the SID tryptophan:lysine ratio increased through 18% of lysine in pigs fed 30% DDGS using soybean meal (SBM) as a source of tryptophan; however, the response was not replicated in a recent trial (Nitikanchana et al., 2011 5 ) that used L-tryptophan to increase the SID tryptophan:lysine ratio from 15 to 21%.This result suggests that tryptophan sources (L-tryptophan vs. SBM) may be important to obtain the growth response.Therefore, we conducted this experiment to evaluate tryptophan sources (L-tryptophan vs. SBM) used to increase the SID tryptophan:lysine ratio in diets containing 30% DDGS for finishing pigs from 157 to 279 lb.

Procedures
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment.
The studies were conducted at a commercial research-finishing barn in southwestern Minnesota.The barns were naturally ventilated and double-curtain-sided. Pens had completely slatted flooring and deep pits for manure storage.Each pen was equipped with a 5-hole stainless steel dry self-feeder and a cup waterer for ad libitum access to feed and water.Daily feed additions to each pen were accomplished through a robotic feeding system (FeedPro; Feedlogic Corp., Willmar, MN) capable of providing and measuring feed amounts for individual pens.
Two replicated studies were conducted using a total of 2,290 gilts (PIC 1050 × 337) with initial BW of 153 and 161 lb in Exp. 1 and 2, respectively, with 26 to 28 gilts per pen and 10 to 13 pens per treatment.Pens of pigs were assigned to 1 of 7 dietary treatments in a completely randomized design while balancing for initial BW within study.Treatments were arranged as a 2 × 3 factorial with the main effects of tryptophan source (L-tryptophan or SBM) and SID tryptophan:lysine ratio (18, 20, and 22% of lysine) with the addition of a control diet that contained 16% SID tryptophan:lysine.Soybean meal and DDGS sources used in each experiment were analyzed for total amino acid content (Table 1; Ajinomoto Heartland LLC, Chicago, IL).These values along with standardized digestibility coefficients from NRC (1998) for SBM and Stein (20076 ) for DDGS were used in diet formulation for each study.The SID tryptophan:lysine ratio was increased by adding crystalline tryptophan to the control diet at the expense of corn or by replacing crystalline lysine and corn with SBM.All  2 through 7).All diets contained 30% DDGS except diets fed in the last phase, in which DDGS level was lowered to 15% to reduce the impact on carcass fat quality and yield.Diets in phase 3 also contained 9 g/ton of Ractopamine HCl (Paylean; Elanco Animal Health, Greenfield, IN).Diet samples were collected from feeders during every phase and stored at −20 º C, then amino acid analysis was conducted on composite samples by Ajinomoto Heartland LLC.
Pens of pigs were weighed and feed disappearance was recorded at d 22, 40, and 56 in Exp.1 and at d 21, 47, and 68 in Exp. 2 to determine ADG, ADFI, and F/G.On d 40 of Exp. 1 and d 47 of Exp. 2, the 5 heaviest pigs per pen were weighed and sold according to the farm's normal marketing procedure.At the end of the trial, pigs were individually tattooed by pen number to allow for carcass data collection.Pigs were transported to JBS Swift and Company (Worthington, MN) for processing and carcass data collection.Hot carcass weights were measured immediately after evisceration, and carcass criteria of backfat depth, and loin depth were collected using an optical probe.Carcass yield percentage was calculated by dividing live weight at the plant with carcass weight at the plant as reported by the processor, and percentage lean was calculated by the processor using a proprietary equation that depended on backfat and loin depth.
The experimental data were analyzed using the MIXED procedure of SAS (SAS Institute, Inc., Cary, NC).Pen was the experimental unit for all data analysis, and experiment was included in the statistical model as a random effect.Significance and tendencies were set at P < 0.05 and P < 0.10, respectively.Analysis of backfat depth, loin depth, and percentage lean were adjusted to a common HCW.Contrast coefficients were used to evaluate linear and quadratic responses to SID tryptophan:lysine ratio (16, 18, 20, and 22%) to compare the two tryptophan sources (L-tryptophan vs. SBM) and to determine linear and quadratic SID tryptophan:lysine ratio by tryptophan source interactions.

Results and Discussion
The analyzed total amino acids were within an acceptable range in both experiments except for a control diet and 22% SID tryptophan:lysine ratio during one phase in Exp. 1 that had a lower lysine level than the formulated value; however, the growth rate was not significantly affected and appeared to be due to random analytic variation.During Phase 1, a linear interaction (P = 0.04; Table 8) occurred between tryptophan source and SID tryptophan:lysine ratio for F/G.This was a result of an improvement in F/G (linear, P < 0.01; Table 8) when SID tryptophan:lysine ratio was increased using SBM whereas the best F/G (quadratic, P = 0.13) was achieved at 18% SID tryptophan:lysine when using L-tryptophan.An interaction in ADG (quadratic, P = 0.02) and ADFI (quadratic, P = 0.01) was observed during Phase 2 due to the difference in pattern of response between sources.For pigs fed supplemental L-tryptophan, the highest ADG and ADFI was for pigs fed 20% with a slight decrease at 22%, whereas pigs fed with SBM also had the greatest response at 20%, but the response was numerically decreased at 22%.No interaction was detected (P > 0.25) during phase 3 when Ractopamine was included in the diets.For the overall period (d 0 to market), an interaction (linear, P = 0.03) occurred between tryptophan source and SID

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tryptophan:lysine ratio for F/G.Increasing the SID tryptophan:lysine ratio improved (quadratic, P < 0.01) F/G, with the best F/G observed at 20% of SID lysine when SBM was a source of tryptophan and 18% of lysine when L-tryptophan was the source.For carcass characteristics, increasing the SID tryptophan:lysine ratio increased (linear, P = 0.01; Table 8) carcass yield when using L-tryptophan as a tryptophan source; however, the greatest yield was observed (quadratic, P = 0.03; Table 8) at an 18% SID tryptophan:lysine ratio when adding SBM resulting in a tryptophan source by SID tryptophan:lysine ratio interaction (linear, P = 0.01).An interaction trend also was observed in loin depth (quadratic, P = 0.08) and lean percentage (quadratic, P = 0.07).Increasing SID tryptophan:lysine ratio with L-tryptophan from 16 to 22% decreased loin depth (quadratic, P < 0.01) and lean percentage, but no differences (P > 0.11) occurred when increasing tryptophan with SBM.
For the main effects, as the SID tryptophan:lysine ratio increased, ADG tended to improve (quadratic, P = 0.10; Table 9) during Phase 1. Feed efficiency improved (linear, P = 0.05) when the SID tryptophan:lysine ratio increased, but ADFI was unaffected (P > 0.41).During Phase 2, increasing the SID tryptophan:lysine ratio resulted in an increase in ADG (quadratic, P = 0.09) and ADFI (linear, P < 0.01), but no differences in F/G (P > 0.19).The greatest ADG and ADFI were observed at the 20% SID tryptophan:lysine ratio.During Phase 3 when Ractopamine HCl was added to diets, ADG increased (quadratic, P = 0.01) and F/G improved (quadratic, P < 0.01) up to a 20% SID tryptophan:lysine ratio.
For the overall period (d 0 to market), ADG and F/G improved (quadratic, P < 0.01) with the increasing SID tryptophan:lysine ratio, but with no differences in ADFI (P > 0.44).This was the result of pigs fed the 20% SID tryptophan:lysine ratio diets having the greatest growth rate and best F/G.For carcass characteristics, pigs fed the 20% SID tryptophan:lysine ratio had the heaviest (quadratic, P = 0.01) HCW.Loin depth was greatest in the control diet (16% SID tryptophan:lysine ratio) and was lowest in the pigs fed 18% SID tryptophan:lysine ratio (quadratic, P = 0.02).Other carcass characteristics were unaffected (P > 0.15) by increasing the SID tryptophan:lysine ratio.
For the main effect of tryptophan source, growth performance during Phase 1 did not differ (P > 0.55; Table 10) between pigs fed the two sources of tryptophan.During Phase 2, pigs fed diets with SBM as a source of tryptophan had greater ADG (P = 0.03) than those fed diets with L-tryptophan as the source; however, there were no differences (P > 0.25) in ADFI or F/G.During Phase 3, ADFI was greater (P = 0.02) when using L-tryptophan as a source of tryptophan compared with using SBM, but ADG and F/G (P > 0.11) did not differ between pigs fed the two sources of tryptophan.For the overall period, a tendency was observed toward greater ADG (P = 0.07) when using SBM as a tryptophan source.Backfat was greater (P = 0.04) and percentage of lean was lower (P = 0.02) in pigs fed with L-tryptophan as the tryptophan source, but no difference in other carcass characteristics was detected.
In this study, an improvement in yield was observed at 18 and 22% SID tryptophan:lysine ratio when using L-tryptophan as a source of tryptophan, and at 18% when using SBM with no improvement afterward.The influence of the tryptophan:lysine ratio on yield and other carcass traits is not conclusive in this study, but increasing the SID tryptophan:lysine ratio in late finishing pigs fed high levels of

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DDGS might offer an opportunity to improve carcass traits, as suggested by Nitikanchana et al. (2011 7,8 ).
Increasing the SID tryptophan:lysine ratio from 16 to 22% quadratically improved ADG and F/G, resulting in an optimum SID tryptophan:lysine ratio of 20% for pigs from 157 to 279 lb.The results of this experiment agree with Barnes (2011 9 ) that concluded the optimum SID tryptophan:lysine ratio for 160-to 265-lb pigs was at least 18%.
Because SBM or L-tryptophan provided a similar response in growth performance, the difference in feed cost when adding SBM or crystalline tryptophan to the diet will be a major factor in choosing the optimal source of tryptophan in diet formulation; however, our study showed that pigs fed with supplemental L-tryptophan deposited slightly more backfat and had a lower lean percentage.The difference in CP might explain these responses; several trials have reported fatter carcasses with a low-CP, amino acid-fortified diet (Smith et al., 1997 10 ; Kerr et al., 1995 11 ) compared with the high-CP diet.Only a small difference in CP (2%) was demonstrated in our trials between diets with L-tryptophan and SBM source; other factors may contribute to these responses.
in meal form and fed in 3 phases from 161 to 205 lb, 205 to 240 lb, and 240 to 270 lb in Exp.1, and 153 to 195 lb, 195 to 244 lb, and 244 to 287 lb in Exp. 2 (Tables

Table 1 .
Amino acid analysis of soybean meal and dried distillers grains with solubles (DDGS) 1

Table 8 .
Effects of tryptophan sources to increasing standardized ileal digestible tryptophan:lysine ratio in diets containing dried distillers grains with solubles (DDGS) on growth performance and carcass characteristics of finishing pigs 1

Table 8 .
Effects of tryptophan sources to increasing standardized ileal digestible tryptophan:lysine ratio in diets containing dried distillers grains with solubles (DDGS) on growth performance and carcass characteristics of finishing pigs 1

Table 9 .
Effects of tryptophan sources to increasing standardized ileal digestible (SID) tryptophan:lysine ratio in DDGS on growth performance and carcass characteristics of finishing pigs (main effect of SID tryptophan:lysine ratio) 1 A total of 2,290 pigs (PIC 1050 × 337; initially 157 lb) were used in 2 replicated studies with 26 to 28 gilts per pen.There were 13 pens per control treatment and 22 to 26 pens for main effect of 18 to 22 SID tryptophan:lysine ratio. 2 Phases were from d 0 to 20, d 20 to 40, and d 40 to 56 in Exp. 1 and from d 0 to 21, d 21 to 47, and d 47 to 68 in Exp.2.3Backfat, loin depth, and lean percentage were adjusted to a common HCW. 1

Table 10 .
Effects of tryptophan sources to increasing standardized ileal digestible tryptophan:lysine ratio in DDGS on growth performance and carcass characteristics of finishing pigs (main effect of tryptophan source) 1 ,290 pigs (PIC 1050 × 337; initially 157 lb) were used in 2 replicated studies with 26 to 28 gilts per pen with 35 to 37 pens per main effect of tryptophan source. 2 Phases were from d 0 to 20, d 20 to 40, and d 40 to 56 in Exp. 1 and from d 0 to 21, d 21 to 47, and d 47 to 68 in Exp.2.3Backfat, loin depth, and lean percentage were adjusted to a common HCW.