Meta-analysis of the response of growing pigs to the isoleucine concentration in the diet

Growth performance, serum parameters, inflammatory responses, intestinal morphology and microbiota of weaned piglets fed 18% crude protein diets with different ratios of standardized ileal digestible isoleucine to lysine

The present study was to explore the Ile requirement of piglets fed 18% crude protein (CP) diets. Two hundred and fifty 28-day-old Duroc × Landrace × Yorkshire piglets (8.37 ± 1.92 kg) were randomly divided into 5 dietary treatments (10 piglets per replicate, 5 barrows and 5 gilts per replicate) with 45%, 50%, 55%, 60%, 65% standardized ileal digestible (SID) Ile-to-Lys ratios, and the SID Lys was formulated to 1.19%. The experimental design consisted of two phases (d 1 to 14 and d 15 to 28). Results showed that average daily gain (ADG) had a tendency to quadratically increase as the SID Ile-to-Lys ratio increased (P = 0.09), and the optimum SID Ile-to-Lys ratios required to maximize ADG were 48.33% and 54.63% for broken-line linear model and quadratic polynomial model, respectively. Different SID Ile-to-Lys ratios had no significant effects on average daily feed intake and gain-to-feed ratio. Dry matter (P < 0.01), CP (P = 0.01), ether extract (P = 0.04), gross energy (P < 0.01) and organic matter (P < 0.01) digestibility increased quadratically. Serum total cholesterol levels decreased linearly (P = 0.01) and quadratically (P < 0.01); aspartate aminotransferase (P < 0.01), interleukin-1β (P = 0.01), and tumor necrosis factor-α (P < 0.01) levels decreased quadratically; immunoglobulin G (P = 0.03) and immunoglobulin M (P = 0.01) concentrations increased quadratically. Serum Ser levels decreased linearly (P < 0.01) and quadratically (P = 0.01); Glu (P = 0.02), Arg (P = 0.05), and Thr (P = 0.03) levels decreased quadratically; Gly (P < 0.01) and Leu (P = 0.01) levels decreased linearly; Ile (P < 0.01) concentration increased linearly. Duodenal villus height (P < 0.01) and villus height to crypt depth ratio (P < 0.01) increased quadratically. The deficiency or excess of Ile decreased short chain fatty acid-producing bacteria abundance and increased pathogenic bacteria abundance. Overall, taking ADG as the effect index, the optimum SID Ile-to-Lys ratios of piglets offered 18% CP diets were 48.33% and 54.63% based on two different statistical models, respectively, and the deficiency or excess of lle negatively affected piglet growth rates and health status.

A Systematic Review and Metanalysis on the Use of Hermetia illucens and Tenebrio molitor in Diets for Poultry

Insect meal as a protein source has been considered a sustainable way to feed animals. H. illucens and T. molitor larvae meal are considered high-protein sources for poultry, also presenting considerable amounts of fatty acids, vitamins, and minerals. However, other potential components in insect meal and insect oil have been more extensively studied in recent years. Chitin, lauric acid, and antimicrobial peptides can present antimicrobial and prebiotic functions, indicating that low levels of their inclusion in insect meal can beneficially affect broilers' health and immune responses. This systematic review was developed to study the impact of insect products on the health parameters of broilers, and a metanalysis was conducted to evaluate the effects on performance. A database was obtained based on a selection of manuscripts from January 2016 to January 2023, following the mentioned parameters. Both H. illucens and T. molitor meal or oil products had positive effects on poultry health status, especially on the ileal and cecal microbiota population, immune responses, and antimicrobial properties. The average daily gain was greater in broilers fed T. molitor meal compared to H. illucens meal (p = 0.002). The results suggest that low levels of insect meal are suitable for broilers, without resulting in negative effects on body weight gain and the feed conversion ratio, while the insect oil can totally replace soybean oil without negative impacts.

Lysine requirements of finishing boars and gilts: A meta-analysis

The expected increase in boar (pig entire male) production while societal concerns for castration increase requires good estimations of their nutrient requirements. In this work, a meta-analytical approach was used to overcome the inconsistent results between studies that compared lysine requirements of boars and gilts. For this meta-analysis, data from 14 different studies analysing the effect of increasing dietary lysine on growth performance of finishing pigs, 70-100 kg average body weight, were extracted from 11 publications. Those studies represented 128 different treatments (53 for boars and 75 for gilts). Diets were reformulated based on NRC (2012) ingredient values to calculate standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and daily SID Lys intake using average daily feed intake (ADFI). As expected, no evidence for differences in ADFI (P = 0.303) was observed between boars and gilts. However, boars grew faster (P < 0.001) and had higher gain to feed (G:F; P < 0.001). The divergent effect of SID Lys:NE on average daily gain (ADG) and G:F was analysed in a quadratic polynomial model showing different parameters for each sex (P < 0.001). Although performance between sexes was similar at low SID Lys:NE, differences were greater at higher SID Lys:NE. Furthermore, broken-line linear, broken-line quadratic (BLQ) and quadratic polynomial (QP) models were fitted to each sex to determine SID Lys:NE and SID Lys daily intake requirements to maximize ADG and G:F. Overall, QP models showed the best fit, and reported that to reach maximum ADG 0.88 (95% CI:[0.82-0.94]) or 1.01 (95% CI:[0.91-1.11]) g SID Lys/MJ, NE was required for gilts and boars, respectively. However, boar ADG was best fitted by BLQ using SID Lys daily intake as independent variable, with the requirement for maximum ADG at 24.2 (95% CI:[21.3-27.2]) g SID Lys/day. The three models reported wide confidence intervals for the requirements at maximum performance, and consequently those were overlapped when comparing boars and gilts. Maximum boars' productive performance when dietary lysine was not limiting was 116% of gilts, and at those levels the amount of SID Lys intake required per kg gain was similar between both sexes. Thus, because ADFI and Lys efficiency of gain was similar, the requirement differences were driven by the increased growth rate and gain to feed ratio between boars and gilts. In conclusion, the present study confirmed a greater productive response of boars compared to gilts when increasing dietary lysine.

Effects on nitrogen balance and metabolism of branched-chain amino acids by growing pigs of supplementing isoleucine and valine to diets with adequate or excess concentrations of dietary leucine

Diets based on high levels of corn protein have elevated concentrations of Leu, which may negatively affect N retention in pigs. An experiment was, therefore, conducted to test the hypothesis that Ile and Val supplementation may overcome the detrimental effects of excess dietary Leu on N balance and metabolism of branched-chain amino acids (BCAA) in growing pigs. A total of 144 barrows (initial body weight: 28.5 kg) were housed in metabolism crates and randomly assigned to 1 of 18 dietary treatments. The basal diet contained 0.98% standardized ileal digestible (SID) Lys and had SID Leu, Val, and Ile ratios to SID Lys of 100%, 60%, and 43%, respectively. Crystalline l-Leu (0% or 2.0%), l-Ile (0%, 0.1%, or 0.2%), and l-Val (0%, 0.1%, or 0.2%) were added to the basal diet resulting in a total of 18 dietary treatments that were arranged in a 2 × 3 × 3 factorial. Urine and fecal samples were collected for 5 d after 7 d of adaptation. Blood, skeletal muscle, and liver samples were collected at the conclusion of the experiment. There were no three-way interactions among the main effects. Excess Leu in diets reduced (P < 0.05) N retention and biological value of protein and increased (P < 0.001) plasma urea N (PUN), but PUN was reduced (P < 0.05) as dietary Val increased. Concentrations of Leu in the liver were greater (P < 0.001) in pigs fed excess Leu diets than in pigs fed adequate Leu diets, but concentrations of BCAA in muscle were greater (P < 0.05) in pigs fed low-Leu diets. Increasing dietary Ile increased (P < 0.001) plasma-free Ile and plasma concentration of the Ile metabolite, α-keto-β-methylvalerate, but the increase was greater in diets without excess Leu than in diets with excess Leu (interaction, P < 0.001). Plasma concentrations of Val and the Val metabolite α-keto isovalerate increased (P < 0.001) with increasing dietary Val in diets with adequate Leu, but not in diets with excess Leu (interaction, P < 0.001). Increasing dietary Leu increased (P < 0.001) plasma-free Leu and plasma concentration of the Leu metabolite, α-keto isocaproate (KIC). In contrast, increased dietary Val reduced (P < 0.05) the plasma concentration of KIC. In conclusion, excess dietary Leu reduced N retention and increased PUN in growing pigs, but Val supplementation to excess Leu diets may increase the efficiency of amino acid utilization for protein synthesis as indicated by reduced PUN.

Evaluating the standardized ileal digestible lysine requirement of 7- to 15-kg weanling pigs fed corn-soybean meal-based diets

Continued genetic improvement necessitates the verification of nutrient requirements for newly developed pig genotypes. Therefore, the objective of this research was to determine the standardized ileal digestible (SID) lysine (Lys) requirement of 7- to 15-kg weanling pigs (TN70 × TN Tempo; Topigs Norsvin) fed a corn-soybean meal-based diet. A total of 144 piglets with an initial BW of 6.51 ± 0.56 kg (mean ± SD) were assigned to one of six diets using a randomized complete block design based on BW to give eight replicate pens with three pigs per pen. The six diets contained 1.00, 1.16, 1.32, 1.48, 1.64, and 1.80% SID Lys, achieved by adding crystalline l-Lys·HCl at the expense of cornstarch. Other indispensable amino acids were provided to meet the requirements. Piglets had free access to diets and water for 21 days. Individual BW of pigs and feed disappearance were recorded weekly and blood samples were collected on day 1, 14, and 21. Average daily gain (ADG) and average daily feed intake were not affected by dietary SID Lys content during the first 7 days. However, the addition of dietary SID Lys quadratically increased (P < 0.05) gain:feed (G:F) during the first 7 days of the experiment. A quadratic increase (P < 0.05) was found in both ADG and G:F when SID Lys content increased in the diets from day 14 to 21. During the overall experimental period, increasing dietary Lys content quadratically increased (P < 0.05) ADG and G:F, whereas plasma urea nitrogen quadratically decreased (P < 0.05) as SID Lys content increased. The SID Lys requirements were estimated for linear and quadratic broken-line models. In conclusion, the SID Lys requirement for optimal growth performance of 7- to 15-kg weanling pigs fed corn-soybean meal-based diets based on linear and quadratic broken-line models were 1.27% (95% confidence interval (CI): [1.01, 1.53]) and 1.30% (95% CI: [0.94, 1.66]) for ADG and 1.27% (95% CI: [1.14, 1.40]) and 1.43% (95% CI: [1.11, 1.75]) for G:F, respectively, thus giving an overall average value of 1.32%.

Improving performance of finishing pigs with added valine, isoleucine, and tryptophan: validating a meta-analysis model

Based on results of a recent meta-analysis, we hypothesized that increased dietary Val, Ile, or Trp could correct possible amino acid interactions because of excess Leu in diets containing high levels of corn protein, namely dried distiller's grains with solubles (DDGS). A total of 1,200 pigs (PIC TR4 × (Fast LW × PIC L02); initially 33.6 ± 0.6 kg) were used in a 103-d study. The 6 dietary treatments were corn-soybean meal (SBM)-DDGS-based as follows: (1) high SBM and low level of l-Lys HCl (HSBM), (2) high l-Lys HCl and moderate Ile, Val, Trp (AA above NRC 2012 estimates; NC), (3) moderate l-Lys HCl and high Ile, Val, and Trp (PC), and PC with either increased (4) L-Val (PC+Val), (5) L-Ile (PC+Ile), or (6) L-Trp (PC+Trp). Pigs fed the NC diet were predicted to have the poorest average daily gain (ADG), the PC diet to be intermediate, and pigs fed the HSBM, PC+Val, PC+Ile, and PC+Trp have the same and highest predicted ADG. In the grower period (34 to 90 kg), ADG was greater (Ρ < 0.05) for the pigs fed HSBM and PC+Val diets than the NC with pigs fed other diets intermediate. Pigs fed HSBM were more (Ρ < 0.05) efficient (G:F) than the NC and PC with pigs fed other diets intermediate. In the finisher period (90 to 136 kg), ADG was greater (Ρ < 0.05) for pigs fed PC+Ile than that of the NC with pigs fed other diets intermediate. Pigs fed PC+Val had greater (Ρ < 0.05) average daily feed intake (ADFI) than the NC with pigs fed other diets intermediate. However, PC+Ile pigs were more (Ρ < 0.05) efficient than PC+Val with pigs fed other diets intermediate. Overall, ADG was greater (Ρ < 0.05) for pigs fed HSBM, PC+Val, and PC+Ile diets than the NC with pigs fed other diets intermediate. Pigs fed the PC+Val diet had greater (Ρ < 0.05) ADFI than the NC with pigs fed other diets intermediate. No differences were detected between treatments for overall G:F or other carcass characteristics. In conclusion, increasing Val or Ile in high l-Lys-HCl-DDGS-based diets improved growth performance compared with pigs fed diets containing high levels of l-Lys HCl without added Val and Ile. These results present evidence that the recently developed meta-analysis can predict the relative differences in overall ADG for pigs fed the NC, PC, PC+Val, and PC+Ile diets; however, the predicted G:F was less accurate. The data demonstrate that the negative effects of high Leu concentrations in corn-DDGS-based diets can be reversed by increasing the ratios of Val and Ile relative to Lys.

Birth weight affects body protein retention but not nitrogen efficiency in the later life of pigs

Exploring factors that might affect nitrogen (N) efficiency in pigs could support the development of precision feeding concepts. Therefore, an experiment was conducted to determine the effects of birth weight (BiW) on N retention, N efficiency, and concentrations of metabolites in plasma and urine related to N efficiency in male pigs of 14 wk of age. BiW of the low BiW (LBW) and high BiW (HBW) pigs was 1.11 ± 0.14 and 1.79 ± 0.12 kg, respectively. Twenty LBW and 20 HBW pigs were individually housed in metabolism cages and were subjected to an N balance study in two sequential periods of 5 d, after an 11-d adaptation period. Pigs were assigned to a protein adequate (A) or protein restricted (R, 70% of A) regime in a change-over design and fed restrictedly 2.8 times the energy requirements for maintenance. Nontargeted metabolomics analyses were performed in urine and blood plasma samples. The N retention in g/d was higher in the HBW than in the LBW pigs (P < 0.001). The N retention in g/(kg BW0.75·d) and N efficiency (= 100% × N retention / N intake), however, were not affected by BiW of the pigs. Moreover, fecal digestibility of N and urinary concentration of N and urea were not affected by BiW of the pigs. The concentration of insulin (P = 0.08) and insulin-like growth factor-1 (IGF-1;P = 0.05) in blood plasma was higher in HBW pigs, whereas the concentration of α-amino N tended to be lower in HBW pigs (P = 0.06). The LBW and HBW pigs could not be discriminated based on the plasma and urinary metabolites retrieved by nontargeted metabolomics. Restricting dietary protein supply decreased N retention (P < 0.001), N efficiency (P = 0.07), fecal N digestibility (P < 0.001), urinary concentration of N and urea (P < 0.001), and concentration of urea (P < 0.001), IGF-1 (P < 0.001), and α-amino N (P < 0.001) in blood plasma. The plasma and urinary metabolites differing between dietary protein regime were mostly amino acids (AA) or their derivatives, metabolites of the tricarboxylic acid cycle, and glucuronidated compounds, almost all being higher in the pigs fed the A regime. This study shows that BiW affects absolute N retention but does not affect N efficiency in growing pigs. Therefore, in precision feeding concepts, BiW of pigs should be considered as a factor determining protein deposition capacity but less as a trait determining N efficiency.

Modeling the effects of standardized ileal digestible isoleucine to lysine ratio on growth performance of nursery pigs. Transl Anim Sci 2017;1:437-447. [PMID: 32704667 PMCID: PMC7204974 DOI: 10.2527/tas2017.0048]

Two experiments evaluated the effects of increasing standardized ileal digestible (SID) Ile:Lys ratio on growth performance of nursery pigs. In both experiments, dietary treatments consisted of 40, 44, 48, 52, 54, 58, or 63% SID Ile:Lys ratio. Diets were formulated using analyzed ingredient AA values and NRC (2012) SID coefficients. A combination of field peas and spray dried blood cells were used to ensure a low enough Ile diet concentration while minimizing the excess of Leu. The experiments consisted of 8 pens per dietary treatment with 5 pigs per pen for a total of 280 nursery pigs per experiment (Exp. 1: PIC 327 × 1,050, initially 6.7 ± 1.0 kg BW; Exp. 2: DNA 600 × 241, initially 6.0 ± 0.97 kg BW). Data were analyzed using mixed models with heterogeneous variance, where appropriate. The dose response was further characterized using quadratic polynomial (QP), broken-line linear (BLL), or broken-line quadratic (BLQ) functional forms. For Exp. 1, diets were initiated 6-d post-weaning and fed for 12-d followed by a common diet from d 12 to 28. From d 0 to 12, increasing dietary SID Ile:Lys ratio increased ADG (linear, P < 0.005) and ADFI (quadratic, P < 0.017) but G:F decreased (quadratic, P < 0.043). For ADG, the QP, BLL, and BLQ models resulted in maximum ADG at 64.7, 52.0, and 52.0 SID Ile:Lys ratios, respectively. For ADFI, the BLL breakpoint occurred at 50.6 and the QP predicted maximum ADFI at 56.2 SID Ile:Lys ratio. In Exp. 2, diets were initiated 6-d post-weaning for 7 pens and 3-d post-weaning for one heavier block and fed for 18-d followed by a common diet from d 18 to 32. From d 0 to 18, ADG and ADFI increased (quadratic, P < 0.016) with no evidence for difference in G:F as SID Ile:Lys ratio increased. For ADG, the QP and BLL had similar fit with breakpoints or maximums occurring at 58.3 and 51.8% SID Ile:Lys ratio, respectively. For ADFI, the BLQ breakpoint occurred at 52.0 SID Ile:Lys and the QP maximum ADFI at 57.2% SID Ile:Lys ratio. In conclusion, broken-line models reported maxima of 52.0% Ile:Lys ratio while quadratic models were as high as 64% of Lys to maximize ADG and ADFI of 6- to 11-kg nursery pigs. However, for the QP models 99% of the maximum response was achieved with a dose comparable to that from the broken line models. Therefore, these results are similar to the NRC (2012) requirement estimate of 51.1 Ile:Lys ratio.

Nontargeted LC-MS Metabolomics Approach for Metabolic Profiling of Plasma and Urine from Pigs Fed Branched Chain Amino Acids for Maximum Growth Performance

The metabolic response in plasma and urine of pigs when feeding an optimum level of branched chain amino acids (BCAAs) for best growth performance is unknown. The objective of the current study was to identify the metabolic phenotype associated with the BCAAs intake level that could be linked to the animal growth performance. Three dose-response studies were carried out to collect blood and urine samples from pigs fed increasing levels of Ile, Val, or Leu followed by a nontargeted LC-MS approach to characterize the metabolic profile of biofluids when dietary BCAAs are optimum for animal growth. Results showed that concentrations of plasma hypoxanthine and tyrosine (Tyr) were higher while concentrations of glycocholic acid, tauroursodeoxycholic acid, and taurocholic acid were lower when the dietary Ile was optimum. Plasma 3-methyl-2-oxovaleric acid and creatine were lower when dietary Leu was optimum. The optimum dietary Leu resulted in increased urinary excretion of ascorbic acid and choline and relatively decreased excretion of 2-aminoadipic acid, acetyl-dl-valine, Ile, 2-methylbutyrylglycine, and Tyr. In conclusion, plasma glycocholic acid and taurocholic acid were discriminating metabolites to the optimum dietary Ile. The optimum dietary Leu was associated with reduced plasma creatine and urinary 2-aminoadipic acid and elevated urinary excretion of ascorbic acid and choline. The optimum dietary Val had a less pronounced metabolic response reflected in plasma or urine than other BCAA.

Concept and application of ideal protein for pigs

Knowledge about the amino acid requirements and the response of pigs to the amino acid supply is essential in feed formulation. A deficient AA supply results in a reduction in performance while an oversupply is costly and leads to excessive nitrogen excretion with a potentially negative environmental impact. Amino acid requirements are determined to a large extent by the protein deposition in the body and, for lactating sows, by the protein exported in the milk. The concept of ideal protein was developed more than 50 years ago and refers to a protein with an amino acid profile that exactly meets the animal’s requirement so that all amino acids are equally limiting for performance. Because Lys typically is the first-limiting amino acid, the ideal amino acid profile is often expressed relative to Lys. Although the ideal protein profile is often assumed to be constant for a given production stage, (small) changes in the ideal protein profile can occur within a production stage. This can be caused by changes in the relative contribution of the different components of amino acid requirements during the productive life on the animal (e.g. changes in the relative contribution of growth and maintenance). Amino acids requirements can be determined experimentally using dose–response studies. The design of the study, the chosen response criterion, and the statistical model affect the requirement estimate. Although considerable experimental work has been carried out to determine the requirements for Lys, Met, Thr, and Trp in growing pigs (and to a lesser extent in sows), little is known about the requirements for the other essential amino acids. Experimental dose–response studies generally focus on the requirement and less on the overall response (i.e. what are the consequences of an amino acid deficiency?). This latter aspect is, to some extent, accounted for in modelling approaches that quantify the response of the animal to the amino acid supply in a dynamic way. The paper describes the origin of ideal protein and illustrates how fundamental concepts of amino acid nutrition have been integrated in practical modeling approaches for the nutrition of growing pigs and sows.

Determining the optimal isoleucine:lysine ratio for ten- to twenty-two-kilogram and twenty-four- to thirty-nine-kilogram pigs fed diets containing nonexcess levels of leucine

Three 21-d experiments were conducted to determine the optimum standardized ileal digestible (SID) Ile:Lys ratio in 10- to 22-kg and 24- to 39-kg pigs. In Exp. 1, 144 Yorkshire pigs (initial BW = 10.2 kg) were assigned to 6 diets with 6 pens per treatment. Diets 1 to 5 were formulated to contain 5 graded SID Ile:Lys (44, 51, 57, 63, and 70%), 1.18% SID Leu, and 0.90% SID Lys (second limiting). Diet 6 (diet 5 with added Lys) was formulated (1.06% SID Lys) as a positive control. Pigs fed diet 6 had higher (P < 0.05) ADG and G:F and lower (P < 0.05) plasma urea N (PUN) than pigs fed diet 5 (P < 0.02), indicating that Lys was limiting in diets 1 to 5. Final BW, ADG, and ADFI increased (linear and quadratic, P < 0.05) while G:F and PUN at d 21 were not affected (P > 0.10) by dietary Ile:Lys. Overall, ADG and ADFI were highest for pigs fed diet 2 (51% SID Ile:Lys). In Exp. 2, 216 Yorkshire pigs (initial BW = 9.6 kg) were assigned to 9 diets with 6 pens per treatment. Diets 1 to 4 contained 0.40, 0.47, 0.54, and 0.61% SID Ile, respectively, and 1.21% SID Lys; diets 5 to 8 contained 0.72, 0.84, 0.96, and 1.08% SID Lys, respectively, and 0.68% SID Ile. Diet 9 was high in both Ile and Lys (0.68% SID Ile and 1.21% SID Lys). All diets contained 1.21% SID Leu. The ADG and G:F increased (linear and quadratic, P < 0.05) as SID Ile:Lys increased (diets 1 to 4 and 9). The ADG and G:F increased (linear, P < 0.05) as SID Lys increased (diets 5 to 9). The PUN at d 21 decreased (linear, P < 0.05) by increasing dietary Ile:Lys. The SID Ile:Lys to optimize ADG was 46% by curvilinear plateau or exponential regression. For G:F, the optimal SID Ile:Lys was 47 and 51% by curvilinear plateau and exponential regressions, respectively. In Exp. 3, 80 pigs (PIC 327 × C23; initial BW = 24.0 kg) were allotted to 5 treatments with 4 pigs per pen. Diets 1 to 5 were formulated to contain 5 graded SID Ile:Lys (39, 46, 53, 61, and 68%), 1.17% SID Leu, and 0.91% SID Lys (second limiting). Final BW and ADG increased (linear and quadratic, P < 0.05) and ADFI increased (linear, P = 0.047) as SID Ile:Lys increased. Using ADG and G:F, the optimum SID Ile:Lys was 54 and 53%, respectively, by curvilinear plateau and exponential regression. The PUN was minimized at 53 and 59% SID Ile:Lys by curvilinear plateau and broken line regression. Overall, the average optimum SID Ile:Lys was approximately 51% for 10- to 22-kg pigs and 54% for 24- to 39-kg pigs fed diets containing nonexcess levels of Leu.

Performance of piglets in response to the standardized ileal digestible phenylalanine and tyrosine supply in low-protein diets

Reducing the CP level of the diet allows for a reduction in N excretion without limiting performance as long as the amino acid (AA) requirements are covered. The availability of crystalline AA has permitted for a considerable reduction in the CP level of diets, practically used in pig nutrition. The adoption of low CP diets and the extent to which the CP content can be reduced further depends on the knowledge of the minimum levels of indispensable AA that maximize growth. The standardized ileal digestible (SID) Phe : Lys and Tyr : Lys requirements and the possibility to substitute Tyr by Phe have never been studied in piglets. The objectives of this study were to estimate these requirements in 10 to 20 kg pig as well as to determine the extent to which Phe can be used to cover the Tyr requirement. In three dose-response studies, six pigs within each of 14 blocks were assigned to six low CP diets (14.5% CP) sub-limiting in Lys at 1.00% SID. In experiment 1, the SID Phe : Lys requirement estimate was assessed by supplementing a Phe-deficient diet with different levels of l-Phe to attain 33%, 39%, 46%, 52%, 58%, and 65% SID Phe : Lys. Because Phe can be used for Tyr synthesis, the diets provided a sufficient Tyr supply. A similar approach was used in experiment 2 with six levels of l-Tyr supplementation to attain 21%, 27%, 33%, 39%, 45% and 52% SID Tyr : Lys. Phenylalanine was supplied at a level sufficient to sustain maximum growth (estimated in experiment 1). The SID Phe : Lys and SID Tyr : Lys requirements for maximizing daily gain were 54% and 40% using a curvilinear-plateau model, respectively. A 10% deficiency in Phe and Tyr reduced daily gain by 3.0% and 0.7%, respectively. In experiment 3, the effect of the equimolar substitution of dietary SID Tyr by Phe to obtain 50%, 57%, and 64% SID Phe : (Phe+Tyr) was studied at two limiting levels of Phe+Tyr. From 57% to 64% SID Phe : (Phe+Tyr), performance was slightly reduced. In conclusion, it is recommended not to use a Phe+Tyr requirement in the ideal AA profile but rather use a SID Phe : Lys of 54% and a SID Tyr : Lys of 40% to support maximal growth.

Response of piglets to the standardized ileal digestible isoleucine, histidine and leucine supply in cereal-soybean meal-based diets

Improving the amino acid (AA) profile of the diet by using l-Lys, l-Thr, dl-Met, l-Trp and l-Val helps to reduce the dietary CP content, thereby reducing nitrogen excretion while maintaining the performance of pigs. Valine is the fifth limiting AA in cereal-soybean meal-based diets. The extent to which the CP content in the diet can be reduced further without compromising performance depends on the requirement of the next limiting AA. In cereal-soybean meal-based diets, Ile, His and Leu may be the limiting AAs after Val, although information on the requirements for these AAs is scarce. Six experiments were conducted to determine the effect of supplementing a low-CP diet with l-Ile, l-His and l-Leu on the performance of pigs weighing 10 to 20 kg. Experiment 1 was designed to determine the most limiting AA with respect to performance among Ile, His and Leu. A diet 10% deficient in Ile, Leu and His relative to the National Research Council (NRC, 1998) requirement estimates tended to decrease daily feed intake and daily gain by 6% and 8%, respectively. A 10% deficiency in His alone had no effect, whereas a 10% deficiency in Ile or Leu slightly reduced daily feed intake and gain. In the remaining experiments, the standardized ileal digestible (SID) Ile : Lys, His : Lys and Leu : Lys requirements were estimated. In Experiments 2, 3, 4, 5 and 6, 14 blocks of six pigs each were assigned to six levels of SID Ile : Lys (40%, 43%, 46%, 49%, 52% and 55%), His : Lys (20%, 24%, 28%, 32%, 36% and 40%), His : Lys (21%, 24%, 27%, 30%, 33% and 36%), Leu : Lys (70%, 78%, 86%, 94%, 102% and 110%) and Leu : Lys (80%, 90%, 100%, 110%, 120% and 130%), respectively. Across experiments, the estimated SID Ile : Lys, His : Lys and Leu : Lys requirements for maximizing daily gain were 49%, 32% and 102%, respectively, using a curvilinear plateau model. When Ile, His and Leu levels were 10% below the requirement estimate, daily gain was reduced by 9%, 3% and 3%, respectively. The results of this study indicate that the Ile requirement estimate is lower than the current NRC requirement estimate, whereas the Leu and His requirements correspond to those proposed by the NRC.