48 Effects of dietary isoleucine and valine supplementation to excess or low leucine diets on nitrogen balance and metabolism of branched-chained amino acids in growing pigs

Abstract An experiment was conducted to test the hypothesis that Ile and Val supplementation may overcome detrimental effects of excess dietary Leu on N balance and metabolism of branched-chained AA (BCAA) in growing pigs. A total of 144 barrows (28.5 ± 2.5 kg) were housed in metabolism crates and randomly assigned to 18 diets. 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. Two levels of synthetic L-Leu (0 or 2.0%), 3 levels of synthetic L-Ile (0, 0.1, or 0.2%), and 3 levels of synthetic L-Val (0, 0.1, or 0.2%) were added to the basal diet for a total of 18 diets 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. Data were analyzed as a 2 × 3 × 3 factorial using the PROC MIXED of SAS with concentrations of Leu, Val, and Ile, and all interactions as main effects and replicate as random effect. No interactions among main effects were observed, but excess Leu in diets reduced (P < 0.05) N retention and biological value of diets and increased (P < 0.05) plasma urea N (PUN). However, PUN was reduced (P < 0.05) as dietary Val increased. Concentrations of BCAA in liver were greater (P < 0.05) in pigs fed excess-Leu diets than in pigs fed low-Leu diets, but concentrations of BCAA in muscle were greater (P < 0.05) in pigs fed low-Leu diets. In conclusion, excess dietary Leu reduced N retention and biological value of diets and increased PUN in growing pigs, but Val supplementation may help overcome negative effects of excess Leu.

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171 Effects of Dietary Valine, Isoleucine, and Tryptophan Supplementations to Diets Containing Excess Leucine on Nitrogen Balance of Growing Pigs

Journal of Animal Science ◽

10.1093/jas/skab054.102 ◽

2021 ◽

Vol 99 (Supplement_1) ◽

pp. 61-61

Author(s):

Woongbi Bi Kwon ◽

Jose A Soto ◽

Hans H Stein

Keyword(s):

Body Weight ◽

Crude Protein ◽

Random Effect ◽

Basal Diet ◽

Growing Pigs ◽

Negative Effects ◽

Initial Body Weight ◽

N Retention ◽

Biological Value ◽

Main Effects

Abstract An experiment was conducted to test the hypothesis that increasing concentrations of dietary Val, Ile, or Trp alone or in combination will alleviate negative effects of excess dietary Leu on N balance of growing pigs. Seventy-two barrows (initial body weight: 33.9 ± 2.6 kg) were housed in metabolism crates and randomly assigned to 1 of 8 diets and 3 blocks with 3 pigs per diet in each block in a 12-d experiment. Treatments were arranged in a 2 × 2 × 2 factorial with the main effects of L-Val (0 or 0.1%), L-Ile (0 or 0.1%), and L-Trp (0 or 0.05%) that were added to a basal diet containing corn and a high-protein corn product (48% crude protein; 5.9% Leu). The basal diet contained 1.00 % standardized ileal digestible (SID) Lys and 171% SID Leu:Lys. Data were analyzed using the PROC MIXED of SAS with concentrations of Val, Ile, and Trp, and all interactions as main effects and replicate as a random effect. No 3-way interactions were observed (Table 1). Results indicated that fecal N output increased if Ile was added to diets without added Val, but that was not the case if Val was added (interaction, P < 0.05). Addition of Ile to diets reduced N retention, but N retention increased with Trp addition to diets without Val addition, but not if Trp was added to diets with added Val (interaction, P < 0.05). The biological value of protein increased if Trp was added to diets without addition of Ile, but if Ile was added, Trp addition did not increase the biological value of protein (interaction, P < 0.05). In conclusion, adding Ile to a diet with excess Leu reduced N retention, but if Trp was added alone or in combination with Ile or Val, N retention increased.

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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

Journal of Animal Science ◽

10.1093/jas/skaa346 ◽

2020 ◽

Vol 98 (11) ◽

Author(s):

Woong B Kwon ◽

Jose A Soto ◽

Hans H Stein

Keyword(s):

Amino Acids ◽

Plasma Concentration ◽

Plasma Concentrations ◽

Basal Diet ◽

Branched Chain Amino Acids ◽

Growing Pigs ◽

Plasma Urea ◽

N Retention ◽

Branched Chain ◽

Dietary Treatments

Abstract 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.

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Excess dietary leucine in diets for growing pigs reduces growth performance, biological value of protein, protein retention, and serotonin synthesis1

Journal of Animal Science ◽

10.1093/jas/skz259 ◽

2019 ◽

Vol 97 (10) ◽

pp. 4282-4292 ◽

Cited By ~ 6

Author(s):

Woong B Kwon ◽

Kevin J Touchette ◽

Aude Simongiovanni ◽

Kostas Syriopoulos ◽

Anna Wessels ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Growth Performance ◽

Growing Pigs ◽

Feed Consumption ◽

Feed Ratio ◽

Plasma Urea ◽

Biological Value ◽

Protein Retention ◽

Branched Chain

Abstract An experiment was conducted to test the hypothesis that excess dietary Leu affects metabolism of branched-chain amino acids (BCAA) in growing pigs. Forty barrows (initial body weight [BW]: 30.0 ± 2.7 kg) were housed individually in metabolism crates and allotted to 5 dietary treatments (8 replicates per treatment) in a randomized complete block design. The 5 diets were based on identical quantities of corn, soybean meal, wheat, and barley and designed to contain 100%, 150%, 200%, 250%, or 300% of the requirement for standardized ileal digestible Leu. Initial and final (day 15) BW of pigs were recorded. Daily feed consumption was also recorded. Urine and fecal samples were collected for 5 d following 7 d of adaptation to the diets. At the end of the experiment, blood and tissue samples were collected to analyze plasma urea N (PUN), plasma and hypothalamic serotonin, tissue BCAA, serum and tissue branched-chain α-keto acids, and messenger ribonucleic acid abundance of genes involved in BCAA metabolism. Results indicated that acid detergent fiber, average daily feed intake, and gain-to-feed ratio decreased (linear, P < 0.05) as dietary Leu increased. A trend (linear, P = 0.082) for decreased N retention and decreased (linear, P < 0.05) biological value of dietary protein was also observed, and PUN increased (linear, P < 0.05) as dietary Leu increased. A quadratic reduction (P < 0.05) in plasma serotonin and a linear reduction (P < 0.05) in hypothalamic serotonin were observed with increasing dietary Leu. Concentrations of BCAA in liver increased (linear, P < 0.001), whereas concentrations of BCAA in skeletal muscle decreased (linear, P < 0.05) as dietary Leu increased. Concentration of α-ketoisovalerate was reduced (linear and quadratic, P < 0.001) in liver, skeletal muscle, and serum, and α-keto-β-methylvalerate was reduced (linear, P < 0.001; quadratic, P < 0.001) in skeletal muscle and serum. In contrast, α-keto isocaproate increased (linear, P < 0.05) in liver and skeletal muscle and also in serum (linear and quadratic, P < 0.001) with increasing dietary Leu. Expression of mitochondrial BCAA transaminase and of the E1α subunit of branched-chain α-keto acid dehydrogenase increased (linear, P < 0.05) in skeletal muscle as dietary Leu increased. In conclusion, excess dietary Leu impaired growth performance and nitrogen retention, which is likely a result of increased catabolism of Ile and Val, which in turn reduces availability of these amino acids resulting in reduced protein retention, and excess dietary Leu also reduced hypothalamic serotonin synthesis.

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282 Effect of formulating diets based on a ratio between STTD Ca and STTD P and the inclusion of phytase on the calcium and phosphorus balance of growing pigs

Journal of Animal Science ◽

10.1093/jas/skaa054.177 ◽

2020 ◽

Vol 98 (Supplement_3) ◽

pp. 103-104

Author(s):

Vanessa Lagos ◽

Mike R Bedford ◽

Hans H Stein

Keyword(s):

Block Design ◽

Random Effect ◽

Growing Pigs ◽

Diet Formulation ◽

Randomized Complete Block Design ◽

Microbial Phytase ◽

P Utilization ◽

P Balance ◽

Main Effects ◽

P Absorption

Abstract An experiment was conducted to test the hypothesis that formulating diets for pigs based on a ratio between standardized total tract digestible (STTD) Ca and STTD P instead of total Ca and STTD P increases the efficiency of Ca and P utilization. Forty barrows (59.4 ± 3.8 kg) were individually housed in metabolism crates and allotted to 4 corn-soybean meal diets and 2 periods of 11 d in a randomized complete block design. Diets were formulated using a 2 × 2 factorial design with 2 Ca requirement estimates (total Ca or STTD Ca) and 2 inclusion levels of microbial phytase (0 or 500 units/kg). Phytase was assumed to release 0.11% STTD P and 0.16% total Ca. Diets were formulated based on requirements for total Ca and STTD P and the ratio between STTD Ca and STTD P was 1.25:1 in diets formulated based on STTD Ca. Fecal and urine samples were collected from feed provided from d 6 to 9. Data for Ca and P balance were analyzed using a model that included the main effects of diet formulation and phytase level, the interaction between main effects, and the random effect of period. Interactions (P < 0.05) between diet formulation and phytase level were observed for Ca intake, Ca in feces, Ca digestibility, Ca retained as a percentage of intake, P digestibility, P absorbed, and P in urine (Table 1). Despite being provided less (P < 0.05) Ca, pigs fed diets formulated based on STTD Ca did not absorb or retain less Ca than pigs fed total Ca diets, but they absorbed more (P < 0.05) P than pigs fed diets formulated based on total Ca. In conclusion, by formulating diets based on values for STTD Ca, P absorption was increased confirming detrimental effects of oversupplying Ca.

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120 Effects of dietary leucine concentration on branched-chain amino acid metabolism in growing pigs

Journal of Animal Science ◽

10.1093/jas/skz122.121 ◽

2019 ◽

Vol 97 (Supplement_2) ◽

pp. 65-66

Author(s):

Woong B Kwon ◽

Kevin J Touchette ◽

Aude Simongiovanni ◽

Kostas Syriopoulos ◽

Anna Wessels ◽

...

Keyword(s):

Growth Performance ◽

Average Daily Gain ◽

Growing Pigs ◽

Feed Ratio ◽

Final Body Weight ◽

Plasma Urea ◽

Biological Value ◽

Branched Chain Amino Acid ◽

Branched Chain ◽

Quadratic Effects

Abstract The hypothesis that excess dietary Leu affects growth performance and metabolism of branched-chain amino acids (BCAA) in growing pigs was tested. Forty barrows (30.0 ± 2.7 kg) were placed in metabolism crates and randomly allotted to 5 diets that contained 100, 150, 200, 250, or 300% of the requirement for standardized ileal digestible Leu. Initial and final body weight of pigs and daily feed provisions were recorded. Urine and fecal samples were collected for 5 d to measure N balance and biological value of diets. At the conclusion of the experiment, blood, brain, liver, and muscle samples were collected and average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio (G:F) were calculated. Orthogonal polynomial contrasts were used to determine linear and quadratic effects of increasing Leu in the diets. Results indicated that ADG, ADFI, and G:F decreased (linear, P < 0.05) as dietary Leu increased (Table 1). A trend (linear, P = 0.082) for decreased N retention and decreased (linear, P < 0.05) biological value of protein was also observed. Plasma urea N increased (linear, P < 0.05) and a quadratic reduction (P < 0.05) in plasma serotonin and a linear reduction (P < 0.05) in cerebral serotonin were observed with increasing dietary Leu. Concentrations of BCAA in liver increased (linear, P < 0.001), concentrations of BCAA in muscle decreased (linear, P < 0.05), concentration of α-keto-isovalerate was reduced (linear and quadratic, P < 0.001) in liver, muscle, and serum, and α-keto-β-methylvalerate was reduced (linear and quadratic, P < 0.001) in muscle and serum, whereas α-keto-isocaproate increased (linear, P < 0.05) in liver and muscle, and in serum (linear and quadratic, P < 0.001) with increasing dietary Leu. In conclusion, excess dietary Leu reduced growth performance and cerebral serotonin and tended to reduce protein synthesis.

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Excessive heating of 00-rapeseed meal reduces not only amino acid digestibility but also metabolizable energy when fed to growing pigs

Journal of Animal Science ◽

10.1093/jas/skaa219 ◽

2020 ◽

Vol 98 (7) ◽

Author(s):

Maryane S F Oliveira ◽

Markus K Wiltafsky-Martin ◽

Hans H Stein

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Basal Diet ◽

Rapeseed Meal ◽

Sole Source ◽

Heating Time ◽

Growing Pigs ◽

Metabolizable Energy ◽

Negative Effects ◽

Ileal Digestibility

Abstract Two experiments were conducted to test the hypothesis that both the degree of heating and the time that heat is applied will affect the concentration of DE and ME, and the apparent ileal digestibility (AID) and the standardized ileal digestibility (SID) of amino acids (AA) in 00-rapeseed meal (00-RSM) fed to growing pigs. The nine treatments were prepared using a conventional 00-RSM that was either not autoclaved or autoclaved at 110 °C for 15 or 30 min or at 150 °C for 3, 6, 9, 12, 15, or 18 min. In experiment 1, 20 growing barrows with an average initial BW of 21.2 ± 1.2 kg were randomly allotted to the 10 diets in a replicated 10 × 4 Youden square with 10 diets and four periods in each square. A corn-based basal diet and nine diets containing corn and each source of 00-RSM were formulated. Urine and fecal samples were collected for 5 d after 7 d of adaptation. In experiment 2, nine diets contained one of the nine sources of 00-RSM as the sole source of AA, and an N-free diet that was used to measure basal endogenous losses of AA and CP was formulated. Twenty growing barrows with an initial BW of 69.8 ± 5.7 kg had a T-cannula installed in the distal ileum and were allotted to a 10 × 7 Youden square design with 10 diets and 7 periods. Ileal digesta were collected on days 6 and 7 of each 7-d period. Results from the experiments indicated that there were no effects of autoclaving at 110 °C on DE and ME or on AID and SID of AA in 00-RSM, but DE and ME, and AID and SID of AA were less (P < 0.01) if 00-RSM was autoclaved at 150 °C compared with 110 °C. At 150 °C, there were decreases (quadratic, P < 0.05) in DE and ME, and in AID and SID of AA as heating time increased. In conclusion, autoclaving at 110 °C did not affect ME or SID of AA in 00-RSM, but autoclaving at 150 °C had negative effects on ME and SID of AA and the negative effects increased as heating time increased.

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Amino acid requirements of growing pigs 5. The interaction between isoleucine and leucine

Animal Science ◽

10.1017/s0003356100002257 ◽

1984 ◽

Vol 38 (2) ◽

pp. 257-261 ◽

Cited By ~ 16

Author(s):

S. J. Taylor ◽

D. J. A. Cole ◽

D. Lewis

Keyword(s):

Amino Acid ◽

Conversion Efficiency ◽

Live Weight ◽

Basal Diet ◽

Growing Pigs ◽

Carcass Quality ◽

Food Conversion ◽

Isoleucine Leucine ◽

Plasma Urea ◽

Food Conversion Efficiency

ABSTRACTThirty-two female growing pigs (25 to 55 kg live weight) were subjected to four dietary treatments combining two levels of isoleucine and two levels of leucine to investigate the effects of leucine supply on the requirement for isoleucine.Results for daily live-weight gain, food conversion efficiency and carcass quality judged by ham dissection indicated that 3·8 g isoleucine per kg diet was marginally adequate for the growing pig in diets containing 13·4 g leucine per kg. An interaction between dietary leucine and isoleucine was demonstrated. Increasing the dietary leucine concentration to 20·4 g/kg clearly resulted in a deficiency of isoleucine in the basal diet, as daily gain, food conversion efficiency and carcass quality were significantly improved by increasing the isoleucine concentration from 3·8 g to 4·5 g/kg diet. Dietary leucine concentration did not influence performance at the higher level of isoleucine supply. Changes in plasma urea and amino acid concentrations confirmed the findings from the growth experiment of the interaction between isoleucine, leucine and valine.

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Effects of the amount and quality of dietary protein on nitrogen metabolism and protein turnover of pigs

British Journal Of Nutrition ◽

10.1079/bjn19870096 ◽

1987 ◽

Vol 58 (2) ◽

pp. 287-300 ◽

Cited By ~ 52

Author(s):

M. F. Fuller ◽

P. J. Reeds ◽

A. Cadenhead ◽

B. Seve ◽

T. Preston

Keyword(s):

Dietary Protein ◽

Protein Turnover ◽

Growing Pigs ◽

Whole Body ◽

Urea Synthesis ◽

Total N ◽

Plasma Urea ◽

Body Protein ◽

N Retention

1. The interrelations between protein accretion and whole-body protein turnover were studied by varying the quantity and quality of protein given to growing pigs.2. Diets with 150 or 290g lysine-deficient protein/kg were given in hourly meals, with or without lysine supplementation, to female pigs (mean weight 47 kg).3. After the animals were adapted to the diets, a constant infusion of [14C]urea was given intra-arterially for 30 h, during the last 6 h of which an infusion of [4,5-3H] leucine was also infused at a constant rate. At the same time, yeast-protein labelled with15N was given in the diet for 50 h.4. The rate of urea synthesis was estimated from the specific radioactivity (SR) of plasma urea. The rate of leucine flux was estimated from the SR of plasma leucine. The irrevocable breakdown of leucine was estimated from the3H-labelling of body water. Total N flux was estimated from the16N-labelling of urinary urea.5. Addition of lysine to the low-protein diet significantly increased N retention, with a substantial reduction in leucine breakdown, but there was no significant change in the flux of leucine or of total N.6. Increasing the quantity of the unsupplemented protein also increased N retention significantly, with concomitant increases in leucine breakdown and in the fluxes of leucine and of total N.7. It is concluded that a doubling of protein accretion brought about by the improvement of dietary protein quality is not necessarily associated with an increased rate of whole-body protein turnover.

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Hydroxy Selenomethionine Improves Meat Quality through Optimal Skeletal Metabolism and Functions of Selenoproteins of Pigs under Chronic Heat Stress

Antioxidants ◽

10.3390/antiox10101558 ◽

2021 ◽

Vol 10 (10) ◽

pp. 1558

Author(s):

Yan Liu ◽

Shenggang Yin ◽

Jiayong Tang ◽

Yonggang Liu ◽

Gang Jia ◽

...

Keyword(s):

Skeletal Muscle ◽

Heat Stress ◽

Growth Performance ◽

Meat Quality ◽

Carcass Traits ◽

Basal Diet ◽

Growing Pigs ◽

Control Group ◽

Encoding Genes

Chronic heat stress (CHS) induces metabolic changes in skeletal muscle from growth to maintenance that jeopardizes growth performance, carcass traits, and meat quality of pigs. We investigated the protective effect of dietary organic selenium (hydroxy-4-methylselenobutanoic acid, OH-SeMet) on CHS-induced skeletal muscle damages of growing pigs, and the corresponding responses of selenoproteins. A total of 40 ((Landrace × Yorkshire) × Duroc) pigs with an average live weight of 49.64 ± 2.48 kg were used in this 4-week trial. Pigs were randomly allotted to 5 groups: The control group was raised on a basal diet in a thermoneutral environment (22 ± 2 °C); and four CHS groups were raised on a basal diet and supplemented with Se 0.0, 0.2, 0.4, and 0.6 mg/kg as OH-SeMet, respectively, in hyperthermal condition (33 ± 2 °C). CHS resulted in significant decrease of growth performance, carcass traits, and meat quality, which were associated with reduced (p < 0.05) serum alkaline phosphatase (ALP) and total superoxide dismutase (T-SOD) and increased (p < 0.05) serum creatine (CK), sarcous heat shock protein 70 (HSP70), glucokinase (GCK), phosphoenolpyruvate carboxykinase (PEPCK), and malondialdehyde (MDA) contents. Meanwhile, four metabolism-related genes and seven selenoprotein encoding genes were abnormally expressed in skeletal muscle. Dietary OH-SeMet addition partially alleviated the negative impact of CHS on carcass traits and improved meat quality. These improvements were accompanied by the increase in Se deposition, the anti-oxidative capacity of serum and muscle, and protein abundance of GPX1, GPX3, GPX4, and SELENOP. Supplementation with 0.6 mg Se/kg (OH-SeMet) restored the sarcous PEPCK, and 0.4 and 0.6 mg Se/kg (OH-SeMet) restored all abnormally expressed metabolism-related and selenoprotein encoding genes. In summary, dietary supplementation with OH-SeMet beyond Se requirement mitigated CHS-induced depression of carcass traits and meat quality of pigs associated with optimal skeletal metabolism, enhanced antioxidant capacity, and regulation of selenoproteins in skeletal muscle of pigs.

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Amino acid requirements of growing pigs. 6. Isoleucine

Animal Science ◽

10.1017/s0003356100031950 ◽

1985 ◽

Vol 40 (1) ◽

pp. 153-160 ◽

Cited By ~ 11

Author(s):

S. J. Taylor ◽

D. J. A. Cole ◽

D. Lewis

Keyword(s):

Amino Acids ◽

Growth Performance ◽

Live Weight ◽

Basal Diet ◽

Essential Amino Acids ◽

Growing Pigs ◽

Food Utilization ◽

Urea Nitrogen ◽

Plasma Urea ◽

Amino Acid Requirements

ABSTRACTThe response of the growing female pig (25 to 55 kg live weight) to increasing dietary isoleucine supplies at two levels of dietary leucine was assessed by measurement of growth rate, food utilization, tissue deposition as indicated by ham dissection and changes in plasma urea concentration. A range of isoleucine concentrations from 3·7 g/kg to 5T g/kg of the diet was derived from a basal diet and seven increments of L-isoleucine. Synthetic L-leucine was added to the basal diet to increase the concentration from 12 g/kg to 15 g/kg to achieve the two levels. The basal diet was formulated using barley, maize, blood meal, yeast protein, fat and tapioca with synthetic amino acids included to maintain at least 9·5 g/kg lysine and adequate concentrations of other essential amino acids and non-essential nitrogen. The 16 diets were replicated four times and fed to 64 female growing pigs once daily according to a restricted feeding scale. Blood samples were taken from each pig at 40 kg live weight for the determination of plasma urea nitrogen.The addition of synthetic leucine to the basal diet had no consistent effect on growth performance or carcass quality, although it did result in elevated levels of plasma urea nitrogen. The response of growth performance and the composition of the ham joint to increasing dietary isoleucine concentration was interpreted by broken line functions which indicated an isoleucine requirement of 4·4 to 4·5 g/kg of the diet.

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