Standardized Ileal Digestible Trp Research Articles

Estimation of digestible tryptophan:lysine ratios for maximum performance, egg quality and welfare of white-egg-laying hens by fitting the different non-linear models

ABSTRACTA total of 360 Hy-Line W-36 hens at 30 wk of age were assigned to 6 dietary treatments that consisted of 6 different (11, 15, 19, 23, 27 and 31) digestible Trp:Lys ratios. Hens were fed the experimental diets from 30 to 36 wk of age. Productive traits were recorded every wk and egg quality was measured at 36 wk of age. Total IgM, IgG, anti-sheep red blood cell antibody titres, plasma corticosterone, serotonine and glucose concentrations and heterophil to lymphocyte ratio (H:L) were determined at wk 6 of the experiment. Results showed a significant improvement (P < .0001) in egg production, egg mass, feed intake, feed conversion ratio and body weight by increasing the standardized ileal digestible (SID) Trp:Lys ratio from 11 to 19. Relative weights of shell (P < .05) and shell strength (P < .06) were affected by dietary treatments. Hens fed graded levels of SID Trp responded by decreasing the H:L ratio in a linear or curvilinear manner (P < .05). The study reported here indicated that the ideal SID Trp:Lys ratio for laying hens ranged from17.5 to 29 based on the response criteria and regression models.

Effects of different dietary tryptophan:lysine ratios and sanitary conditions on growth performance, plasma urea nitrogen, serum haptoglobin and ileal histomorphology of weaned pigs.

A total of 180 mixed-sex pigs (Duroc × (Yorkshire × Landrace); average initial body weight of 7.36±0.2kg) weaned at 21±1 days were fed corn-soybean meal-wheat-based diets to determine the optimal standardized ileal digestible (SID) tryptophan to lysine ratio (Trp:Lys) in a 2×5 factorial arrangement (two sanitary conditions: clean (CL) and unclean (UCL), and five dietary treatments (SID Trp:Lys (16, 18, 20, 22 and 24%)). In each sanitary condition, blood was collected on days 0 and 14 to determine plasma urea nitrogen and on day 14, ileal tissue (one pig per pen) was collected for the measurement of gut morphology. Pigs kept under UCL conditions had lower growth rate (P<0.05) than under CL conditions. Under CL conditions, the estimated optimal SID Trp:Lys for average daily gain (ADG) was 19.7% whereas under UCL conditions these values were 20.5% and 19.0% for ADG and gain-to-feed ratio, respectively. Under CL conditions, increasing SID Trp:Lys reduced (linear, P=0.05) plasma urea nitrogen concentration but had no effect (P>0.10) on villous height (VH), crypt depth ( CD) and VH:CD. In conclusion, an SID Trp:Lys to optimize ADG for pigs raised under UCL conditions was higher (4%) than CL conditions.

Effects of dietary tryptophan:lysine ratio on the reproductive performance of primiparous and multiparous lactating sows

The objective of this study was to determine the effects of dietary tryptophan (Trp) to lysine (Lys) ratio on the performance of lactating sows. Thirty primiparous and 195 multiparous lactating sows (Landrace×Yorkshire) were allocated on the basis of parity, body weight, and backfat to 5 dietary treatments according to a randomized complete block design with 5 blocks of farrowing date. The 5 experimental diets contained 0.16%, 0.19%, 0.23%, 0.26%, or 0.29% standardized ileal digestible (SID) Trp and SID Lys level was identical (0.87%) for all diets, with the Trp:Lys ratio being 0.18, 0.22, 0.26, 0.30, and 0.33, respectively. Sows received their assigned lactation diets from day 109 of gestation to weaning. Litter size was standardized to 10–12 piglets within 2 days after farrowing. The average lactation length was 19 days and no creep feed was provided. Changes of sow body weight and backfat during lactation, weaning-to-estrus interval, litter size and weight, litter weight gain, preweaning piglet mortality, and performance of subsequent parity (total born alive, stillborns, and mummies) were recorded. A quadratic pattern of body weight loss (P=0.046), backfat loss (P=0.067), and average daily feed intake (P=0.096) with increasing Trp level was observed for the primiparous sows during lactation, and the losses were minimized with the SID Trp:Lys ratio of 0.25 (0.22% SID Trp) and average feed intake was maximized with the SID Trp:Lys ratio of 0.22 (0.19% SID Trp) according to a segmented regression analysis model. Nevertheless, preweaning piglet mortality of the primiparous sows increased linearly and quadratically (P<0.001) as Trp level increased. On the contrary, piglet mortality of the multiparous sows decreased linearly (P=0.031) with increasing dietary Trp and the mortality was noticeably reduced when the SID Trp:Lys ratio reached 0.26 (0.23% SID Trp). Furthermore, stillborn piglet numbers of multiparous sows in the subsequent parity decreased linearly (P=0.035) with increasing level of Trp. Other parameters were not significantly (P>0.05) influenced by the dietary treatment. In conclusion, our results indicate that the optimal Trp:Lys ratio for lactating sows is between 0.22 and 0.26.

An update on modeling dose-response relationships: Accounting for correlated data structure and heterogeneous error variance in linear and nonlinear mixed models.

Advanced methods for dose-response assessments are used to estimate the minimum concentrations of a nutrient that maximizes a given outcome of interest, thereby determining nutritional requirements for optimal performance. Contrary to standard modeling assumptions, experimental data often present a design structure that includes correlations between observations (i.e., blocking, nesting, etc.) as well as heterogeneity of error variances; either can mislead inference if disregarded. Our objective is to demonstrate practical implementation of linear and nonlinear mixed models for dose-response relationships accounting for correlated data structure and heterogeneous error variances. To illustrate, we modeled data from a randomized complete block design study to evaluate the standardized ileal digestible (SID) Trp:Lys ratio dose-response on G:F of nursery pigs. A base linear mixed model was fitted to explore the functional form of G:F relative to Trp:Lys ratios and assess model assumptions. Next, we fitted 3 competing dose-response mixed models to G:F, namely a quadratic polynomial (QP) model, a broken-line linear (BLL) ascending model, and a broken-line quadratic (BLQ) ascending model, all of which included heteroskedastic specifications, as dictated by the base model. The GLIMMIX procedure of SAS (version 9.4) was used to fit the base and QP models and the NLMIXED procedure was used to fit the BLL and BLQ models. We further illustrated the use of a grid search of initial parameter values to facilitate convergence and parameter estimation in nonlinear mixed models. Fit between competing dose-response models was compared using a maximum likelihood-based Bayesian information criterion (BIC). The QP, BLL, and BLQ models fitted on G:F of nursery pigs yielded BIC values of 353.7, 343.4, and 345.2, respectively, thus indicating a better fit of the BLL model. The BLL breakpoint estimate of the SID Trp:Lys ratio was 16.5% (95% confidence interval [16.1, 17.0]). Problems with the estimation process rendered results from the BLQ model questionable. Importantly, accounting for heterogeneous variance enhanced inferential precision as the breadth of the confidence interval for the mean breakpoint decreased by approximately 44%. In summary, the article illustrates the use of linear and nonlinear mixed models for dose-response relationships accounting for heterogeneous residual variances, discusses important diagnostics and their implications for inference, and provides practical recommendations for computational troubleshooting.

Day-night behaviour and performance of barrows and gilts (70–100 kg) fed low protein diets with different levels of tryptophan and B6 vitamin

Tryptophan (Trp) is involved in regulation of animal behaviour, since it originates serotonin and melatonin, especially in low crude protein diets, and Trp metabolism requires B6 vitamin (B6) as enzymatic cofactor. The objective of this study was to feed low protein diets with different levels of standardized ileal digestible (SID) Trp and B6 for barrows and gilts (70–100kg) and to measure day-night behaviour, performance and carcass traits. In experiment 1 (Exp. 1) sixty four barrows (initial BW=70.77±2.07kg) were used, and in experiment 2 (Exp. 2) sixty four gilts (initial BW=70.52±2.95kg) were used. In both experiments a 2×4 factorial arrangement of treatments was used: two B6 levels (1 and 5mgkg−1) and four levels of SID Trp (Exp. 1: 0.130, 0.155, 0.180, 0.205%; and Exp. 2: 0.140, 0.167, 0.194, 0.221%). Day-night behaviour was recorded at the end of weeks 1, 2 and 3 (days 7, 14 and 21) during 24h. Scan-sampling was used to determine time-budget behaviour. Growth performance and carcass traits were measured at the end of the experimental period, when animals reached about 100kg BW (in average 26days). In Exp. 1 (barrows), stationary behaviour in daytime period (from 6:00h to 18:00h) increased quadratically (P=0.005) as Trp content in diets increased from 0.130 to 0.165%, but it decreased until 0.205% of SID Trp. Interacting behaviour in night-time period (from 18:00h to 6:00h) was affected by B6 (P=0.031). Sleeping behaviour decreased linearly (P=0.003) as Trp content in diets increased from 0.130 to 0.205% and feeding behaviour showed quadratic response (P=0.008) to SID Trp (0.161%). In Exp. 2 (gilts) sleeping behaviour in daytime period decreased quadratically (P=0.001) as SID Trp content in diets increased from 0.140 to 0.179%, but it decreased until 0.221% of SID Trp. Feeding behaviour was affected by the interaction Trp×B6 (P=0.030) as supplementary B6 (5mgkg−1) decreased visits to feeder up to 0.194% Trp content. Sleeping behaviour in night-time period was affected by the interaction Trp×B6 (P=0.030) once supplementary B6 (5mgkg−1) markedly decreased time spent sleeping when compared to basal B6 (1mgkg−1) as Trp levels increased in diets. Feeding behaviour responded quadratically (P=0.001) to Trp (0.173%). In both experiments performance variables and carcass traits were not different (P>0.05) neither for Trp nor B6. SID Trp levels from 0.130 to 0.205% (barrows) and 0.140 to 0.221% (gilts) even as B6 content (1 or 5mgkg−1) in diets had no consistent effects on behaviour and did not alter performance of pigs.

042 An update on modeling dose–response relationships: Accounting for correlated data structures and heterogeneous variance in linear and nonlinear mixed models

Advanced methods for dose–response assessments are used to estimate concentrations of a nutrient that optimize a given outcome of interest, thereby determining nutritional requirements for optimal performance. Traditionally, many dose–response methods use a fixed-effects framework that assumes mutually independent observations with homogeneous variances. Yet experimental data often present a design structure that includes correlations between observations (e.g., blocking, nesting, etc.) as well as heterogeneity of variances that can mislead inference if disregarded. Our objective is to demonstrate practical implementation of computationally intensive linear and nonlinear mixed models methodology to describe dose–response relationships accounting for correlated data structure and heterogeneous variances. To illustrate, we model data from a randomized complete block design study to evaluate the standardized ileal digestible (SID) Trp:Lys dose–response on G:F of nursery pigs. A base linear mixed model was fit to explore the functional form of G:F relative to Trp:Lys and assess model assumptions, in particular residual homoscedasticity. Next, we fitted 3 competing dose–response mixed models to G:F, namely a quadratic polynomial (QP), a broken-line linear (BLL) ascending model, and a broken-line quadratic (BLQ) ascending model, all of which included heteroskedastic specifications, as dictated by the base model, and used parameter estimates from the base model as initial values. The GLIMMIX procedure of SAS (version 9.4; SAS Inst. Inc., Cary, NC) was used to fit the base and QP models and the NLMIXED procedure was used to fit the nonlinear models. We further illustrate the use of a grid-search approach to facilitate convergence and parameter estimation in nonlinear mixed models, as this seemed to be the most common implementation problem. Model fit between competing dose–response models was compared using maximum likelihood–based Bayesian information criterion (BIC). The QP, BLL, and BLQ models fitted on G:F of nursery pigs yielded BIC values of 353.7, 343.4, and 345.2, respectively, indicating a better fit of BLL followed closely by BLQ. The BLL breakpoint estimate of the SID Trp:Lys was 16.5% (95% confidence interval [CI] 16.1–17.0), whereas the BLQ estimate was 16.0% (95% CI 15.5–16.6). Importantly, accounting for heterogeneous variance enhanced inferential precision as the breadth of the CI for mean breakpoint decreased by approximately 44%, from 95% CI 15.8 to 17.4 to 95% CI 16.1 to 17.0 SID Trp:Lys. In summary, we illustrate the use of linear and nonlinear mixed models for dose–response relationships accounting for heterogeneous residual variances, discuss important diagnostics and their implications for inference, and provide practical recommendations for computational troubleshooting.

Simultaneous determination of standardized ileal digestible tryptophan and lysine for barrows from 15 to 30 kg live weight

The digestible amino acid (AA) determination of ingredients, or experimental diets, are essential in obtaining the real levels of AA that are being studied, as well as of other indispensable AA, because the lack of a single indispensable AA may limit pig growth performance. Two experiments were conducted to determine the optimum levels and the ideal ratio of standardized ileal digestible (SID) Trp and Lys for barrows from 15 to 30kg of live weight. The first experiment (Exp. 1) was conducted to determine the SID AA content of the basal diet used in the growth performance study (Exp. 2). Ten crossbred barrows (21.5±1.6kg live weight) were used in Exp. 1. Pigs were fed a basal diet and a protein free diet to determine the SID of Trp, Lys, and all other indispensable AA of the basal diet. In Exp. 2, 64 barrows (15.0±1.6kg) were allotted to 16 diets in a 4×4 factorial arrangement of treatments (1.55, 1.85, 2.15, and 2.45g SID Trp and 9.72, 11.12, 12.52, and 13.92g SID Lys/kg) with 4 replications per treatment. In both Exp. 1 and 2, each pig was considered as an experimental unit. Growth performance, Longissimus muscle (LM), backfat thickness, and plasma urea nitrogen (PUN) were evaluated. Average daily feed intake and average daily gain increased linearly (P<0.05) with increasing levels of SID Trp. There was a quadratic effect (P=0.04) of dietary SID Trp and Lys levels on the gain:feed, and the optimal levels were estimated to be 2.1 (0.65g/Mcal ME) and 11.98g/kg (3.71g/Mcal ME), respectively, resulting in a SID Trp:Lys of 17.5:100. A quadratic effect of SID Trp (P=0.021) and Lys (P=0.026) levels on LM was observed, and the optimum levels were 2.08 and 11.36g/kg diet, respectively, with a Trp:Lys of 18.3:100. The amount of PUN decreased linearly (P=0.004) as SID Lys increased. For pigs used in our study (between 15 and 30kg live weight), the SID Trp and SID Lys requirements are 2.10 and 11.98g/kg, respectively. The corresponding Trp:Lys are 17.5:100.

Effects of standardized ileal digestible tryptophan: lysine ratio on growth performance of nursery pigs.

Two experiments were conducted to estimate the standardized ileal digestible (SID) Trp:Lys ratio requirement for growth performance of nursery pigs. Experimental diets were formulated to ensure that lysine was the second limiting AA throughout the experiments. In Exp. 1 (6 to 10 kg BW), 255 nursery pigs (PIC 327 × 1050, initially 6.3 ± 0.15 kg, mean ± SD) arranged in pens of 6 or 7 pigs were blocked by pen weight and assigned to experimental diets (7 pens/diet) consisting of SID Trp:Lys ratios of 14.7%, 16.5%, 18.4%, 20.3%, 22.1%, and 24.0% for 14 d with 1.30% SID Lys. In Exp. 2 (11 to 20 kg BW), 1,088 pigs (PIC 337 × 1050, initially 11.2 kg ± 1.35 BW, mean ± SD) arranged in pens of 24 to 27 pigs were blocked by average pig weight and assigned to experimental diets (6 pens/diet) consisting of SID Trp:Lys ratios of 14.5%, 16.5%, 18.0%, 19.5%, 21.0%, 22.5%, and 24.5% for 21 d with 30% dried distillers grains with solubles and 0.97% SID Lys. Each experiment was analyzed using general linear mixed models with heterogeneous residual variances. Competing heteroskedastic models included broken-line linear (BLL), broken-line quadratic (BLQ), and quadratic polynomial (QP). For each response, the best-fitting model was selected using Bayesian information criterion. In Exp. 1 (6 to 10 kg BW), increasing SID Trp:Lys ratio linearly increased ( 0.05) ADG and G:F. For ADG, the best-fitting model was a QP in which the maximum ADG was estimated at 23.9% (95% confidence interval [CI]: [<14.7%, >24.0%]) SID Trp:Lys ratio. For G:F, the best-fitting model was a BLL in which the maximum G:F was estimated at 20.4% (95% CI: [14.3%, 26.5%]) SID Trp:Lys. In Exp. 2 (11 to 20 kg BW), increasing SID Trp:Lys ratio increased ( 0.05) ADG and G:F in a quadratic manner. For ADG, the best-fitting model was a QP in which the maximum ADG was estimated at 21.2% (95% CI: [20.5%, 21.9%]) SID Trp:Lys. For G:F, BLL and BLQ models had comparable fit and estimated SID Trp:Lys requirements at 16.6% (95% CI: [16.0%, 17.3%]) and 17.1% (95% CI: [16.6%, 17.7%]), respectively. In conclusion, the estimated SID Trp:Lys requirement in Exp. 1 ranged from 20.4% for maximum G:F to 23.9% for maximum ADG, whereas in Exp. 2 it ranged from 16.6% for maximum G:F to 21.2% for maximum ADG. These results suggest that standard recommendations may underestimate the SID Trp:Lys requirement for nursery pigs from 11 to 20 kg BW.

Optimum standardized ileal digestible tryptophan to lysine ratio for pigs weighing 7–14 kg

The objective of the present study was to evaluate the optimum ratio of standardized ileal digestible (SID) Trp to Lys for pigs after weaning. A total of 96 female pigs were allocated to 1 of 6 diets containing 0.13, 0.15, 0.17, 0.19, 0.21, and 0.23 SID Trp:Lys, with 16 individually housed pigs/treatment. The diets contained similar crude protein (154g/kg), NE (10.5MJ/kg), and SID Lys (10.9g/kg). Average daily feed intake (ADFI), average daily gain (ADG), and gain to feed ratio (G:F) were determined for a 21-d period. Blood and urine samples were collected on d 8 and 15. Urea concentration in plasma and urine decreased (P<0.001) concurrently with increasing SID Trp:Lys. The ADFI, ADG, and G:F improved (P<0.001) with increasing SID Trp:Lys. By fitting by a curvilinear-plateau model, minimum SID Trp:Lys to support optimum ADFI, ADG, and G:F were estimated to be 0.20, 0.20, and 0.16, respectively. By fitting a broken-line model, the minimum SID Trp:Lys was estimated to be 0.18, 0.18, and 0.15 for optimum ADFI, ADG, and G:F, respectively. In conclusion, growth performance of pigs weighing 7–14kg increased up to 0.20 SID Trp:Lys.

Modeling the Effects of Standardized Ileal Digestible Tryptophan:Lysine Ratio on Growth Performance of 65- to 275-lb Pigs

The objective of this study was to model the effects of standardized ileal digestible (SID) Trp:Lys ratio on growth performance of 65to 275-lb pigs. The present experiment, along with three previous experiments from Goncalves et al. (2014), were used in the analysis. For all studies, dietary treatments consisted of SID Trp:Lys ratios of 14.5, 16.5, 18.0, 19.5, 21.0, 22.5, and 24.5%. The experiments were 21 d in duration and used corn and soybean meal-based diets with 30% dried distillers grains with solubles formulated to be deficient in Lys at the end of each of the experiments. In the current experiment, a total of 975 gilts (337 × 1050; PIC, Hendersonville, TN) were used with initial BW of 234.1 ± 6.8 lb and final BW of 274.9 ± 10.4 (mean ± SD). Pens of pigs were blocked by weight and assigned to one of the seven dietary treatments in a randomized complete block design. There were 6 pens/treatment with 20 to 24 pigs per pen. For 235 to 275 lb-pigs, increasing SID Trp:Lys improved ADG (quadratic, P < 0.022), ADFI (linear, P < 0.001), and F/G (linear, P < 0.001). Data from all experiments were then combined for analysis using linear and non-linear mixed models with random effects of experiment and weight block nested within experiment allowing for heterogeneous variances. Competing models included broken-line linear (BLL), broken-line quadratic (BLQ), and quadratic polynomial (QP). In the combined analysis for ADG, QP was the best fitting model and estimated SID Trp:Lys requirement at 23.5% (95% CI: [22.7, 24.3%]). In the combined analysis for F/G, BLL and BLQ had comparable fit and estimated SID Trp:Lys requirements at 16.9% (95% CI: [16.0, 17.8%]) and 17.0% (95% CI: [15.0, 18.9%]), respectively. Thus, the estimated mean requirements for SID Trp:Lys for 65to 275-lb pigs ranged from 16.9% for optimum mean F/G to 23.5% for maximum mean ADG. Furthermore, 95% of the maximum estimated mean ADG was obtained by feeding 17.6% SID Trp:Lys and 98% of the maximum estimated mean ADG was obtained by feeding 19.8% SID Trp:Lys.

Effect of dietary tryptophan to lysine ratio on growth of young pigs fed wheat–barley or corn based diets

There is considerable variation in recommendations for optimum tryptophan (Trp):lysine (Lys) ratio in diets of starter pigs up to 35kg body weight (BW) which may partly be due to differences in the composition of experimental diets, the experimental approach, and the mathematical model used for data analysis. The objective of this study was therefore to determine the Trp:Lys ratio required for maximum response of pigs (15–35kg BW; BW) offered a wheat–barley–soybean meal (WB) or a corn–soybean meal (C) based diet. Three mathematical models were applied to test to which extent the choice of model will affect the estimate of optimum Trp:Lys ratio.A 4-week dose–response growth study was conducted with 880 crossbred castrated male and female pigs. The pigs were randomly allotted to eight dietary treatments per diet type. A Trp-deficient diet (T1) was formulated for each diet type that met animals׳ requirements for all amino acids other than Trp (1.4g standardized ileal digestible (SID) Trp/kg diet) and Lys (10.5g SID Lys/kg diet). L-Trp was added to T1 diets to create six additional diets per diet type (T2–T7) with SID Trp concentrations increasing from 13.1% to 19.7% in WB based and from 14.3% to 20.9% in C based diets. To test whether Lys was the second-limiting amino acid, a Lys adequate diet was formulated (T8) for each diet type by adding crystalline Lys to the respective T7 diet. Pigs had free access to feed and water. Individual BW was recorded every two weeks and pen feed intake daily.For both diet types BW gain increased (P<0.01) and feed to gain ratio improved (P<0.05) with increasing Trp:Lys ratio. In the Trp-deficient diets feed intake was reduced by 100 and 60g/day in WB and C based diets, respectively, compared to diets 2–8. According to the broken-line, curvilinear plateau, and exponential models, highest BW gain was reached at Trp:Lys ratios of 16.8%, >19.7%, and >19.7% for BW based, and 18.0%, >20.9%, and >20.9% for C based diets, respectively. The respective ratios for the feed to gain ratio were 17.0%, 18.5%, and >19.7% and 19.9%, >20.9%, and >20.9% for WB and C based diets, respectively. The results confirm published ratios determined in WB based diets and indicate a slightly higher optimum ratio in C based diets. However, the mathematical model used for data analysis, the chosen response parameter, and the target performance level strongly affect estimates of the optimum dietary Trp:Lys ratio.

Estimation of the optimal ratio of standardized ileal digestible tryptophan to lysine for finishing barrows fed low protein diets supplemented with crystalline amino acids

Optimum standardized ileal digestible (SID) tryptophan (Trp) to lysine (Lys) ratio was estimated for 67&amp;ndash;96 kg barrows fed low protein diets supplemented with crystalline amino acids (AA). One hundred and fifty Yorkshire &amp;times; Landrace barrows, with an average initial body weight (BW) of 67.3 &amp;plusmn; 3.2 kg, were used in a 28-day feeding trial. All dietary treatments were based on corn, wheat bran, and soybean meal and were formulated to provide 10.5% crude protein and 12.6 MJ/kg metabolizable energy. The dietary SID Lys was set at 0.61% ensuring that Lys was marginally deficient for barrows of this weight range. Graded levels of crystalline l-Trp were added to the basal diet to produce diets providing SID Trp to Lys ratios of 0.131, 0.164, 0.197, 0.230, and 0.262. There were improvements in weight gain (linear and quadratic effect P &amp;lt; 0.01) and feed intake (linear effect P = 0.04) with increasing dietary SID Trp to Lys ratio. Increased SID Trp to Lys ratio resulted in a decrease in the serum urea nitrogen (SUN) content (linear and quadratic effect P &amp;lt; 0.01). The serum concentration of Trp increased with increasing dietary SID Trp to Lys ratio (linear effect P = 0.03, quadratic effect P = 0.08). Estimates of the optimum SID Trp to Lys ratios were 0.203, 0.197, and 0.214 for weight gain, feed conversion ratio, and SUN, respectively, using a broken-line model while a quadratic model produced optimum SID Trp to Lys ratios of 0.251, 0.224, and 0.249 for the same parameters. The results of this experiment indicate that the SID Trp to Lys ratio for finishing barrows is at least 0.203, which is higher than the SID ratio of Trp to Lys currently recommended by the National Research Council (NRC, 2012).

Validating a dietary approach to determine amino acid:lysine ratios for pigs (2014)

Standardized ileal digestible (SID) amino acid:lysine (AA:Lys) ratio experiments are commonly conducted to estimate the AA requirement of pigs relative to lysine (Lys) and allow for accurate diet formulation. The objective of the studies herein was to validate a dietary approach to determine the optimal SID AA:Lys ratio for pigs using tryptophan (Trp) as a model. Four 21-d experiments were conducted in which pigs (337 × 1050; PIC) were fed corn-soybean meal–based diets with 30% corn dried distillers grains with solubles (DDGS). A total of 1,188, 1,232, 1,204, and 1,183 pigs with initial BW of 28.5 ± 0.4, 50.1 ± 1.3, 127.0 ± 2.5, and 192.5 ± 2.6 lb were used in experiments 1, 2, 3, and 4, respectively. Each experiment had 11 pens per treatment with 24 to 28 pigs per pen. In Experiment 1, each pen housed the same number of barrows and gilts, whereas in Experiments 2 to 4 only gilts were used. Dietary treatments were: (1) High CP, High Lys, and High Trp:Lys ratio (HHH); (2) Low CP, High Lys, and High Trp:Lys ratio (LHH); (3) Low CP, Low Lys, and High Trp:Lys ratio (LLH); and (4) Low CP, Low Lys, and Low Trp:Lys ratio (LLL). The SID Trp concentrations used were 14.5 vs. 20% of Lys, CP was at least 3 percentage units different, and SID Lys levels were 0.01 percentage unit above the estimated requirement at the expected initial BW and 0.10 or 0.05 percentage units below requirement at the expected final BW of the Experiment 1 (nursery) and Experiments 2, 3, and 4 (finishing), respectively. In Experiment 1, decreasing CP (HHH vs. LHH) did not influence ADG but increased (P < 0.05) F/G. Decreasing Lys (LHH vs. LLH) and decreasing the SID Trp:Lys ratio (LLH vs. LLL) reduced (P < 0.05) ADG and increased (P < 0.05) F/G. In Experiment 2, decreasing CP (HHH vs. LHH) did not affect ADG but increased (P < 0.05) F/G. Decreasing Lys (LHH vs. LLH) and the SID Trp:Lys ratio (LLH vs. LLL) decreased (P < 0.05) ADG and increased (P < 0.05) F/G. In Experiment 3, decreasing CP (HHH vs. LHH) or Lys (LHH vs. LLH) did not influence ADG or F/G. Decreasing the SID Trp:Lys ratio (LLH vs. LLL) reduced (P < 0.05) ADG and increased (P < 0.05) F/G. In Experiment 4, decreasing CP (HHH vs. LHH) did not influence ADG but increased (P

Prediction of the concentration of standardized ileal digestible amino acids in distillers dried grains with solubles1

Values for the concentration of standardized ileal digestible (SID) CP, Lys, Met, Thr, and Trp from 34 sources of distillers dried grains with solubles (DDGS) were obtained from a series of 5 experiments with the objective of predicting the concentration of SID AA from physical and chemical assays. The concentration of NDF, ADF, hemicellulose, acid detergent insoluble CP (ADICP), and KOH soluble protein (SolCP) were measured and calculated in all DDGS sources. Likewise, particle size was measured and color of each source of DDGS was determined with a Minolta colorimeter and HunterLab spectrometer and was expressed as lightness (L*), redness (a*), and yellowness (b*). The HunterLab spectrometer also provided optical density that was recorded between 400 and 700 nm. Front face fluorescence was measured at 360 nm excitation and recorded from 380 to 600 nm. Multiple linear regression and principal components analyses were performed to predict the concentration of SID AA among DDGS sources, and predicted means as well as predicted residual sums of squares (PRESS) were calculated to estimate accuracy and precision of the model. Some correlations (P < 0.05) were observed between ADF, hemicellulose, ADICP, and SolCP with SID CP and AA but were generally low (r < 0.51). There was a greater association (R(2) = 0.40; P < 0.05) between L* and SID Lys among DDGS sources when L* was less than 50 than when samples had L* values greater than 50. In addition, a* was negatively correlated (P < 0.05) with SID CP (r = -0.41), Lys (r = -0.59), and Met (r = -0.50) whereas b* tended to be positively correlated (P < 0.10) with SID Lys (r = 0.31) and Trp (r = 0.30) and was correlated (P = 0.05) with SID Met (r = 0.43) and Thr (r = 0.36). There were no correlations between NDF or particle size with SID CP and AA. Optical density, along with CP, was highly predictive of SID Lys (R(2) = 0.97; PRESS = 0.05), Thr (R(2) = 0.94; PRESS = 0.06), and Trp (R(2) = 0.93; PRESS = 0.004) but not SID Met (R(2) = 0.39; PRESS = 0.12). Front face fluorescence was also highly predictive of SID Lys (R(2) = 0.99; PRESS = 0.07), Met (R(2) = 0.95; PRESS = 0.05), Thr (R(2) = 0.99; PRESS = 0.008), and Trp (R(2) = 0.99; PRESS = 0.006). In conclusion, correlations between ADICP, SolCP, NDF, particle size, and color measurements with SID AA concentrations were poor, but optical density and front face fluorescence methods appear to provide good predictions of SID AA concentrations in DDGS. However, these prediction equations need to be validated using samples of DDGS from a separate data set.

Effects of standardized ileal digestible tryptophan:lysine in diets containing 30% dried distillers grains with solubles on finishing pig performance and carcass traits1,2

Two experiments were conducted to determine the effects of standardized ileal digestible (SID) Trp:Lys in grow-finish swine diets containing 30% dried distillers grains with solubles (DDGS). Within each experiment, crystalline Lys and Trp replaced soybean meal to alter the dietary SID Trp:Lys concentration but maintain minimum ratios of other AA to Lys. In Exp. 1, 638 pigs (36.3 kg initial BW) were used in a 105-d trial (6 pens per treatment). Pens of pigs were randomly allotted to 1 of 4 dietary treatments with SID Trp:Lys of 14.0, 15.0, 16.5, and 18.0%. From d 0 to 42, as Trp:Lys increased, ADG increased (quadratic; P = 0.05) and ADFI tended to increase (quadratic; P = 0.07) with no changes in G:F. Both ADG and ADFI were maximized at Trp:Lys of 16.5%. From d 42 to 105, increasing SID Trp:Lys increased (linear; P < 0.001) ADG and ADFI. Unlike data from d 0 to 42, the response was linear through the greatest SID Trp:Lys of 18.0%. Overall (d 0 to 105), increasing SID Trp:Lys increased (linear; P < 0.001) final BW, ADG, ADFI, and HCW. In Exp. 2, 1,214 pigs (66.3 kg initial BW) were used in a 73-d finishing trial (9 pens per treatment). Pens of pigs were randomly allotted to 1 of 5 dietary treatments with SID Trp:Lys of 15.0, 16.5, 18.0, and 19.5 and the 15.0% Trp:Lys diet with l-Trp added to achieve 18.0% SID Trp:Lys. Overall (d 0 to 73), ADG, ADFI, G:F, and final BW improved (linear; P < 0.03) as dietary SID Trp:Lys increased through 19.5%. No differences were found in growth performance between the 2 diets containing 18.0% SID Trp:Lys. For carcass traits, increasing SID Trp:Lys resulted in increased HCW (linear; P = 0.01) and a tendency toward a decreased (quadratic; P = 0.09) backfat depth and fat-free lean index (FFLI), with pigs fed diets containing 16.5 and 18.0% SID Trp:Lys having increased FFLI and lower backfat depth compared with pigs fed 15.0 and 19.5% SID Trp:Lys. Pigs fed the diet with added crystalline Trp tended to have increased (P = 0.08) backfat depth and decreased FFLI (P = 0.10) compared with pigs fed the same SID Trp:Lys without crystalline Trp. The results indicated that the optimal SID Trp:Lys was 16.5% from 36.3 to 72.6 kg but at least 19.5% from 72.6 to 120.2 kg in corn-soybean meal diets containing 30% DDGS.

Estimation of the ideal standardized ileal digestible tryptophan to lysine ratio for growing pigs fed low crude protein diets supplemented with crystalline amino acids

Tryptophan is typically regarded as the second or third limiting amino acid (AA) in low-crude protein (CP), corn-soybean meal based diets fed to growing swine. However, there is limited data available concerning the ideal standardized ileal digestible (SID) Trp to Lys ratio for growing pigs fed low-CP diets supplemented with crystalline AA. Therefore, the aim of this study was to evaluate the Trp requirement for 25–50kg pigs, expressed as a SID Trp to Lys ratio, using swine housed under commercial conditions. In Experiment 1, 144 growing pigs were used to identify a diet deficient in Lys. The pigs were fed either a high-CP (18.6%) diet with 1.02% SID Lys or one of two low-CP diets (CP content reduced by four percentage units but supplemented with crystalline Lys, Trp, Met, Thr, Ile, and Val) providing 0.9 or 1.02% SID Lys, respectively. Each diet was fed to six pens containing eight pigs (4 barrows and 4 gilts) per pen. The weight gain (688g/day) of pigs receiving the low-CP diet containing 0.9% SID Lys was lower (P=0.03) than that of pigs fed diets containing 1.02% SID Lys with a high- (758g/day) or low-CP (747g/day) content, confirming that this diet was deficient in Lys and, therefore, 0.9% SID Lys was used in the basal diet fed in Experiment 2. Experiment 2 was a dose–response study involving 300 growing pigs, in which graded levels of crystalline Trp were used to produce five diets providing SID Trp to Lys ratios of 13, 16, 19, 22, or 25%. Each diet was fed to six pens containing ten pigs (five barrows and five gilts) per pen. Serum Ile, Leu, Phe, and Trp concentrations linearly increased (P<0.05) as the dietary SID Trp to Lys ratio increased. In contrast, serum urea nitrogen (SUN) and Ala concentrations linearly decreased (P<0.05) as the dietary SID Trp to Lys ratio increased. The SID Trp to Lys ratios that maximized weight gain, feed conversion ratio, and SUN were 19.7, 20.0, and 20.8% using a linear-breakpoint model and 22.6, 23.2, and 23.6% using a curvilinear–plateau model. Taking an average of these six values, we conclude that the optimum SID Trp to Lys ratio is at least 22% for 25–50kg growing pigs fed low-CP diets supplemented with crystalline AA.

Effect of susceptibility to enterotoxigenic Escherichia coli F4 and of dietary tryptophan on gut microbiota diversity observed in healthy young pigs

Healthy weaned pigs susceptible to enterotoxigenic Escherichia coli F4 (ETEC) require more tryptophan (Trp) to maximize their performance. This may be related to an effect on intestinal microbiota. We studied the intestinal bacterial diversity of healthy pigs with different susceptibility to ETEC and fed different Trp levels. Thirty-six littermate weaned pigs were selected to obtain a set potentially formed of 50% ETEC-susceptible and 50% non-susceptible pigs, based on a Mucin 4 gene polymorphism. Pigs were fed a diet with 0.17 (TrpL) or 0.22 (TrpH) standardized ileal digestible Trp:Lys ratio for 21 days. Slaughtered pigs were classified into non-susceptible, mildly susceptible, and susceptible, by testing ETEC adhesion to intestinal villi. Bacterial diversity in jejunum content was assessed by the 16S rRNA gene-targeted denaturing gradient gel electrophoresis (DGGE) fingerprinting analysis and expressed by the Shannon index. Susceptible pigs had a reduced bacterial diversity, particularly with TrpL diet (p=0.003). The ETEC adhesion class affected the quantification of enterobacteria DNA (p=0.027). One DGGE band, which referred to Clostridium bartlettii, was not evidenced in all the susceptible pigs; less DNA from this microbe was quantified by RT-PCR in the jejunum from TrpH susceptible pigs (p=0.025) compared to TrpL. The gene expression for β-galactoside α-2,3-sialyltransferase 1 was higher in jejunal tissue of ETEC-susceptible pigs (p=0.019). In studies on pig gut microbiota, the presence of intestinal receptors for ETEC should be considered because of their contribution to a reduced bacterial diversity. This effect could be partially reversed by dietary Trp addition.

Immune system stimulation reduces the efficiency of tryptophan utilization for body protein deposition in growing pigs1

The effect of immune system stimulation (ISS) on N retention and Trp utilization in pigs fed Trp-limiting diets was evaluated using 36 growing pigs (20.0 ± 1.1 kg BW; 3 blocks of 12 barrows). Pigs were randomly assigned to 1 of 5 diets (Diet 1, 2, 4, and 5, n = 7; Diet 3, n = 8) and fed restrictively at 800 g/d. Diets 1 to 4 were generated by blending Diet 1 with a protein-free supplement and were calculated to contain varying amounts of standardized ileal digestible (SID) Trp (1.31, 1.05, 0.80, and 0.55 g/kg). To confirm that Trp was the first-limiting AA in Diets 1 to 4, an additional diet was used (Diet 5), which was equivalent to Diet 4 and contained 0.34 g/kg of added Trp. After a 5-d adaptation period, pigs were injected every 2 d with increasing amounts of E. coli lipopolysaccharide to induce ISS (initial dose 20 μg/kg BW, increasing 15% each subsequent injection). Whole body N balance was measured in 3 periods: before immune stimulation (pre-ISS) and during ISS in 2 subsequent periods (ISS-1, 3 d; ISS-2, 4 d). Regression analysis was used to estimate the marginal efficiency of Trp utilization for whole body protein deposition (PD; N retention × 6.25). Plasma concentrations of acute-phase proteins and white blood cell counts increased (P < 0.001) and plasma albumin decreased (P < 0.001) during ISS. Nitrogen retention increased (P < 0.001) as Trp intake increased. Nitrogen retention was numerically greater but not statistically different between Diet 5 (added Trp diet) and Diet 4. Whole body N retention was less (P < 0.05) during ISS due primarily to an increase (P < 0.05) in urinary N excretion. There was a linear response (P < 0.05) in N retention, urinary N, and total excreted N to increasing Trp intake. Protein deposition increased by 88.2 ± 5.2, 82.5 ± 5.1, and 92.5 ± 3.4 g/d for each additional g/d of SID Trp intake during pre-ISS, ISS-1, and ISS-2, respectively, but the intercept was not different (-32.3 g/d). The slope of the response of PD to increasing Trp intake (based on the common intercept) was less during ISS-1 compared with pre-ISS (P = 0.01) or ISS-2 (P = 0.002) but not different between pre-ISS and ISS-2. Immune system stimulation reduced N retention in pigs fed limiting dietary Trp. The efficiency of Trp utilization for protein deposition was also reduced during ISS, indicating that the Trp requirement for PD is increased ∼7% during an inflammatory state.

Valine and isoleucine requirement of 20- to 45-kilogram pigs1,2

Three experiments were conducted to determine the Val and Ile requirements in low-CP, corn-soybean meal (C-SBM) AA-supplemented diets for 20- to 45-kg pigs. All experiments were conducted for 26 to 27 d with purebred or crossbred barrows and gilts, which were blocked by initial BW. Treatments were replicated with 5 or 6 pens of 3 or 4 pigs per pen. At the beginning of Exp. 1 and the end of all experiments, blood samples were obtained from all pigs to determine plasma urea N (PUN) concentrations. All diets were C-SBM with 0.335% supplemental Lys to achieve 0.83% standardized ileal digestible (SID) Lys, which is the Lys requirement of these pigs. In Exp. 1, 0, 0.02, 0.04, 0.06, 0.08, or 0.10% L-Val was supplemented to achieve 0.51, 0.53, 0.55, 0.57, 0.59, or 0.61% dietary SID Val, and Thr, Trp, Met, and Ile were supplemented to maintain Thr:Lys, Trp:Lys, TSAA:Lys, and Ile:Lys ratios of 0.71, 0.20, 0.62, and 0.60, respectively. Also, supplemental Gly and Glu were added to all diets to achieve 1.66% Gly + Ser and 3.28% Glu, which is equal to the Gly + Ser and Glu content of a previously validated positive control diet that contained no supplemental AA. Treatment differences were considered significant at P < 0.10. Valine addition increased ADG, ADFI, and G:F in pigs fed 0.51 to 0.59% SID Val (linear, P < 0.08), but ADG and ADFI were decreased at 0.61% SID Val (quadratic, P ≤ 0.10). On the basis of ADG and G:F, the SID Val requirement is between 0.56 and 0.58% in a C-SBM diet supplemented with AA. In Exp. 2 and 3, 0, 0.02, 0.04, 0.06, or 0.08% L-Ile was supplemented to achieve 0.43, 0.45, 0.47, 0.49, or 0.51% dietary SID Ile, and Thr, Trp, Met, and Ile were supplemented to maintain Thr:Lys, Trp:Lys, TSAA:Lys, and Val:Lys ratios of 0.71, 0.20, 0.62, and 0.74, respectively. Also, supplemental Gly and Glu were added to achieve 1.66% Gly + Ser and 3.28% Glu as in Exp. 1. Data from Exp. 2 and 3 were combined and analyzed as 1 data set. Daily BW gain, ADFI, and G:F were not affected by Ile additions to the diet; however, ADFI was decreased among pigs fed the diet with 0.45% SID Ile (P < 0.10) compared with pigs fed the 0.43% SID Ile diet. Broken-line analysis requirements could not be estimated for the combined data from Exp. 2 or 3. The results of this research indicate that the SID Val requirement is between 0.56 to 0.58% (0.67 to 0.70 SID Val:Lys), and the Ile requirement is adequate at 0.43% SID Ile (0.52 SID Ile:Lys) for 20- to 45-kg pigs.

Standardized ileal digestible tryptophan-to-lysine ratios in growing pigs fed corn-based and non-corn-based diets1,2

Two 21-d experiments were conducted to determine the optimum standardized ileal digestible (SID) Trp:Lys in growing pigs fed corn-based diets compared with non-corn-based diets. The primary response variables in both experiments were ADG and plasma urea N (PUN) concentrations with the optimum SID Trp:Lys determined using broken-line analysis. Experiment 1 evaluated the optimum SID Trp:Lys in growing pigs fed corn-based diets consisting primarily of corn with minor inclusion of Canadian field peas and corn gluten meal to keep the SID Trp:Lys low. This experiment used 120 crossbred pigs (initial BW: 25.73 ± 2.46 kg) that were blocked by sex and initial BW and allotted to 5 SID Trp:Lys with 5 pens each for the first 4 treatments and 4 pens for the last treatment and 5 pigs/pen. Diets were formulated by the addition of supplemental Trp to create various SID Trp:Lys (12.77, 14.07, 15.50, 16.91, and 17.94%) with a constant SID Lys of 0.66%, which was determined to be 83% of the Lys requirement for pigs at this location. As the SID Trp:Lys increased from 12.77 to 17.94%, ADG increased (0.562, 0.648, 0.788, 0.787, and 0.815 kg/d) linearly (P < 0.001) and quadratically (P = 0.009), resulting in an optimum SID Trp:Lys of 15.73% (P < 0.001). Plasma urea N decreased (10.43, 9.30, 8.21, 8.55, and 9.25 mg/dL) linearly (P = 0.069) and quadratically (P = 0.015), resulting in an optimum SID Trp:Lys of 15.83% (P = 0.007). Experiment 2 evaluated the optimum SID Trp:Lys in growing pigs fed non-corn-based diets consisting primarily of barley and Canadian field peas, with smaller proportions of corn and wheat. Experiment 2 used 120 crossbred pigs (initial BW: 28.49 ± 2.92 kg) that were allotted to 5 increasing SID Trp:Lys (13.05, 14.32, 15.59, 16.85, and 18.11%; 0.66% SID Lys) in the same manner as Exp. 1. As SID Trp:Lys increased in Exp. 2, ADG increased linearly (P = 0.007) with the optimum SID Trp:Lys of 15.99% (P = 0.048). Plasma urea N concentrations decreased linearly (P = 0.056) and quadratically (P = 0.067) as SID Trp:Lys increased, resulting in an optimum SID Trp:Lys of 15.29% (P = 0.009). Averaging the break point values for ADG and PUN obtained from broken-line analysis for Exp. 1 and 2 produced optimum SID Trp:Lys of 15.78 and 15.64%, respectively. Based on the results from these 2 experiments, it seems that the optimum SID Trp:Lys is virtually unaffected by the dietary feedstuffs used as long as the diets are formulated on an SID AA basis.