Supplementing l-leucine to a low-protein diet increases tissue protein synthesis in weanling pigs

New insights into the effects of dietary amino acid composition on meat quality in pigs: A review

Pork is an affordable protein source with higher nutrient density. In recent years, meat quality in pigs is getting increasing attention, which has a direct impact on the economic value of pork. Dietary amino acids play a key role in pig production, not only regulating pig growth and health, but also contributing significantly to meat quality. In this review, we discuss the effect of skeletal muscle composition on meat quality. Importantly, we summarize the levels of essential amino acids (EAAs), such as lysine, methionine, threonine, tryptophan and branched-chain amino acids (BCAAs), in diets for finishing pigs to improve meat quality. The beneficial effects of flavor amino acids on meat quality, including flavor production, muscle fiber-type composition and intramuscular fat deposition, are further systematically summarized. We also focus on the impact of dietary amino acid levels on environmental benefits, although research in this area is still limited. Considering that the previously established EAA requirements are based on the principle of maximizing growth rate and feed conversion, this review will provide new insights into the effects of dietary amino acids on aspects of meat quality and highlight the current gaps to promote future research.

Productive, Physiological, and Environmental Implications of Reducing Crude Protein Content in Swine Diets: A Review

Pig production is one of the most important providers of high-quality proteins and amino acids (AAs) to human nutrition. In this sector, feeding has an important economic and environmental impact. A strategy to reduce production costs and negative sustainability effects is reducing dietary crude protein (CP) contents with or without AA supplementation. This review addresses the different aspects related to this strategy, particularly the effects on growth performance and pork traits in piglets and growing and finishing pigs, as well as the physiological molecular mechanisms' underlying effects. Insight is also provided into the effects of dietary CP reduction on the productive performances of alternative pig production systems and breeding boars and sows. Finally, an overview is conducted on the effects of dietary CP reduction on ammonia, odor, and greenhouse gas emissions arising from pig production systems. Overall, CP reduction may lead to production losses, albeit they can be, to some extent, hindered by adequate AA supplementation. Losses are particularly relevant during the post-weaning phase, whereas in finishing pigs, it may bring additional benefits, such as high intramuscular fat contents in some markets or improved gut barrier function with benefits to the animals' health and welfare, as well as decreased ammonia emissions to the environment.

Tuna Dark Muscle Feeding Improved the Meat Quality of Holland Mini-Piglets and Modulated the Gut Microbiota

Pork is one of the most widely produced and consumed meats in the world, and it is also an important source of animal protein. The continuous rise in feed prices has forced the pig industry to consider adding cost-effective alternative feed to pig diets. In this study, we aimed to explore the beneficial effects of tuna dark muscle as a nutritional supplement on the growth performance, serum lipids and antioxidant levels of Holland mini-piglets, as well as on the odor and volatile substances of pork and the gut microbiota. Two-month-old male mini-piglets (n = 24) were fed a control diet or supplemented with either 2% (LD) or 4% (HD) tuna dark muscle for 8 weeks. The use of tuna dark muscle at low and high dosages significantly increased the average daily weight gain, but it showed no significant effect on organ indices or blood lipids. In addition, dark muscle treatment significantly increased the antioxidant capacity, characterized by increased SOD and GSH-Px activities, and it decreased the content of MDA in serum. Moreover, tuna dark muscle feeding shifted the odor of rib muscle and tendon meat away from that of the control group, while similar odor patterns were observed in the longissimus dorsi muscle. Among these volatile substances, hexanal, nonanal, and heptanal increased in response to dietary tuna dark muscle and were regarded as indispensable contributors to the feeding. Furthermore, dietary tuna dark muscle modulated the gut microbiota of the piglets, increasing the abundance of beneficial bacteria such as butyric acid-producing bacteria, and reduced the abundance of harmful bacteria. The feeding strategy reported in this study not only reduces the production costs of pork but also utilizes tuna processing by-products in an environmentally friendly way.

The impact of dietary Laminaria digitata and alginate lyase supplementation on the weaned piglet liver: A comprehensive proteomics and metabolomics approach

The brown seaweed Laminaria digitata, a novel feedstuff for weaned piglets, has potentially beneficial prebiotic properties. However, its recalcitrant cell wall challenges digestion in monogastrics. Alginate lyase is a promising supplement to mitigate this issue. This study's aim was to investigate the impact of incorporating 10% dietary Laminaria digitata, supplemented with alginate lyase, on the hepatic proteome and metabolome of weaned piglets. These diets introduced minor variations to the metabolome and caused significant shifts in the proteome. Dietary seaweed provided a rich source of n-3 PUFAs that could signal hepatic fatty acid oxidation (FABP, ACADSB and ALDH1B1). This may have affected the oxidative stability of the tissue, requiring an elevated abundance of GST for regulation. The presence of reactive oxygen species likely inflicted protein damage, triggering increased proteolytic activity (LAPTM4B and PSMD4). Alginate lyase supplementation augmented the number of differentially abundant proteins, which included GBE1 and LDHC, contributing to maintain circulating glucose levels by mobilizing glycogen stores and branched-chain amino acids. The enzymatic supplementation with alginate lyase amplified the effects of the seaweed-only diet. An additional filter was employed to test the effect of missing values on the proteomics analysis, which is discussed from a technical perspective. SIGNIFICANCE: Brown seaweeds such as Laminaria digitata have prebiotic and immune-modulatory components, such as laminarin, that can improve weaned piglet health. However, they have recalcitrant cell wall polysaccharides, such as alginate, that can elicit antinutritional effects on the monogastric digestive system. The aim of this study was to evaluate the effect of a high level of dietary L. digitata and alginate lyase supplementation on the hepatic metabolism of weaned piglets, using high throughput Omics approaches.

Effects of dietary leucine on growth, antioxidant capacity, immune response, and inflammation in juvenile yellow catfish Pelteobagrus fulvidraco

The experiment was conducted to investigate the effects of dietary leucine on growth, antioxidant capacity, immune response, and inflammation in juvenile yellow catfish. Five diets were formulated to contain five dietary leucine levels: 12.00 (control), 19.00, 26.00, 33.00, and 40.00 g kg-1. Each diet was randomly assigned to triplicate groups of 30 juvenile fish (5.02 ± 0.15 g) twice daily to apparent satiation for 56 days. Weight gain rate, specific growth rate, and activities of liver superoxide dismutase, glutathione peroxidase, and serum lysozyme, as well as immunoglobulin M content, significantly increased with increase in dietary leucine levels up to 26.00 g kg-1, but those values decreased significantly with a further increase in dietary leucine. On the contrary, the lowest malondialdehyde content was found in 26.00 and 33.00 g kg-1 leucine groups. The expression levels of IGF 1 and MYF 5 genes in muscle were significantly upregulated with increase in dietary leucine levels up to 26.00 g kg-1, but the expression of MSTN level showed the opposite trend. The lowest expression levels of IL 8 and TNFɑ genes in the liver were found in 26.00 g kg-1 leucine groups. The quadratic regression analysis on weight gain, specific growth rate, and feed conversion ratio against dietary leucine levels indicated that the optimal dietary leucine requirement was estimated to be 26.84-27.00 g kg-1of the dry diet.

l-Leucine supplementation reduces growth performance accompanied by changed profiles of plasma amino acids and expression of jejunal amino acid transporters in breast-fed intra-uterine growth-retarded piglets

Previously, we provided an evidence that l-Leucine supplementation facilitates growth performance in suckling piglets with normal birth weight. However, it remains hitherto obscure weather breast-fed piglets displaying intra-uterine growth restriction (IUGR) show a similar effect in response to l-Leucine provision. In this study, 7-d-old sow-reared IUGR piglets were orally administrated with l-Leucine (0, 0·7, 1·4 or 2·1 g/kg BW) twice daily for 2 weeks. Increasing leucine levels hampered the growth performance of suckling IUGR piglets. The average daily gain of IUGR piglets was significantly reduced in 1·4 g/kg BW and 2·1 g/kg BW l-Leucine supplementation groups (P < 0·05). Except for ornithine and glutamine, the plasma concentrations of other amino acids were abated as l-Leucine levels increased (P < 0·05). Leucine supplementation led to reduction in the levels of urea, blood ammonia, blood glucose, TAG and total cholesterol, as well as an elevation in the level of LDL-cholesterol in suckling IUGR piglets (P < 0·05). In addition, 1·4 g/kg BW of l-Leucine enhanced the mRNA expression of ATB0,+, whereas decreased the mRNA abundances of CAT1, y + LAT1, ASCT2 and b0,+AT in the jejunum (P < 0·05). Concomitantly, the jejunum of IUGR piglets in l-Leucine group contains more ATB0,+ and less SNAT2 protein than in the control (P < 0·05). Collectively, l-Leucine supplementation impairs growth performance in breast-fed IUGR piglets, which may be associated with depressed nutritional conditions and alterations in the uptake of amino acids and the expression of amino acid transporters in the small intestine.

Dietary Leucine Improves Fish Intestinal Barrier Function by Increasing Humoral Immunity, Antioxidant Capacity, and Tight Junction

This study attempted to evaluate the possible impact and mechanism of leucine (Leu) on fish intestinal barrier function. One hundred and five hybrid Pelteobagrus vachelli ♀ × Leiocassis longirostris ♂ catfish were fed with six diets in graded levels of Leu 10.0 (control group), 15.0, 20.0, 25.0, 30.0, 35.0, and 40.0 g/kg diet for 56 days. Results showed that the intestinal activities of LZM, ACP, and AKP and contents of C3, C4, and IgM had positive linear and/or quadratic responses to dietary Leu levels. The mRNA expressions of itnl1, itnl2, c-LZM, g-LZM, and β-defensin increased linearly and/or quadratically (p < 0.05). The ROS, PC, and MDA contents had a negative linear and/or quadratic response, but GSH content and ASA, AHR, T-SOD, and GR activities had positive quadratic responses to dietary Leu levels (p < 0.05). No significant differences on the CAT and GPX activities were detected among treatments (p > 0.05). Increasing dietary Leu level linearly and/or quadratically increased the mRNA expressions of CuZnSOD, CAT, and GPX1α. The GST mRNA expression decreased linearly while the GCLC and Nrf2 mRNA expressions were not significantly affected by different dietary Leu levels. The Nrf2 protein level quadratically increased, whereas the Keap1 mRNA expression and protein level decreased quadratically (p < 0.05). The translational levels of ZO-1 and occludin increased linearly. No significant differences were indicated in Claudin-2 mRNA expression and protein level. The transcriptional levels of Beclin1, ULK1b, ATG5, ATG7, ATG9a, ATG4b, LC3b, and P62 and translational levels of ULK1, LC3Ⅱ/Ⅰ, and P62 linearly and quadratically decreased. The Beclin1 protein level was quadratically decreased with increasing dietary Leu levels. These results suggested that dietary Leu could improve fish intestinal barrier function by increasing humoral immunity, antioxidative capacities, and tight junction protein levels.

Effect of Isoleucine and Added Valine on Performance, Nutrients Digestibility and Gut Microbiota Composition of Pigs Fed with Very Low Protein Diets

Little is known whether a combination Ile and added Val improves the growth of pigs offered very low protein (VLP) diets through changes in nutrients digestibility and gut microbiota. The objective of this study was to investigate the effect of a mixture of Val above and Ile at NRC levels on growth, nutrient digestibility and gut microbiota in pigs fed with VLP diets. Forty, weaned piglets were assigned to: positive control: normal-protein-diet; negative control (NC): VLP diet supplemented with first four limiting amino acids; VA: NC with Val above NRC; IL: NC with Ile at NRC level; VAIL: NC with Val above and Ile at NRC levels. While both VAIL and VA groups completely recovered the inhibitory effects of VLP diets on feed intake, only VAIL partially recovered the negative effects of VLP diets on growth performance. VAIL and VA increased the thermal radiation and decreased the digestibility of nitrogen. NC increased the relative abundance of Pasteurellaceae and Enterobacteriaceae in the colon. VAIL had a higher abundance of colonic Actinobacteria, Enterococcus, and Brevibacillus and the colon content of VA was more enriched with Mogibacterium. Overall, VAIL partially improved the growth performance which is likely linked with alterations in gut microbiota composition.

Free Amino Acid-Enriched Diets Containing Rapidly but Not Slowly Digested Carbohydrate Promote Amino Acid Absorption from Intestine and Net Fluxes across Skeletal Muscle of Pigs

BACKGROUND

The approach to matching appropriate carbohydrates alongside free amino acids to achieve optimal muscle growth remains unclear.

OBJECTIVES

We investigated whether the consumption of a diet containing rapidly digested carbohydrate and free amino acids can enhance intestinal absorption and muscular uptake of amino acids in pigs.

METHOD

Twelve barrows (28 kg; 11 wk old) with catheters installed in the portal vein, mesenteric vein, femoral artery, and femoral vein were randomly assigned to consume 1 of 2 free amino acid-enriched diets (3.34%) containing rapidly [waxy corn starch (WCS)] or slowly [pea starch (PS)] digested carbohydrate for 27 d. Blood was collected to determine the fluxes of plasma glucose and amino acids across the portal vein and the hindlimb muscle. Dietary in vitro carbohydrate digestive rates were also determined. Data were analyzed using repeated-measures (time × group) ANOVA.

RESULTS

Carbohydrate in vitro cumulative digestibility at 30 and 240 min was 69.00% and 95.25% for WCS and 23.25% and 81.15% for PS, respectively. The animal experiment presented WCS increased individual amino acids (lysine, 0.67 compared with 0.53 mmol/min; threonine, 0.40 compared with 0.29 mmol/min; isoleucine, 0.33 compared with 0.22 mmol/min; glutamate, 0.51 compared with 0.35 mmol/min; and proline, 0.51 compared with 0.27 mmol/min), essential amino acid (EAA; 3.26 compared with 2.65 mmol/min), and branched-chain amino acid (BCAA; 0.86 compared with 0.65 mmol/min) fluxes across the portal vein during 8 h postprandial, as well as individual amino acids (isoleucine, 0.08 compared with 0.02 mmol/min; leucine, 0.06 compared with 0.02 mmol/min; and glutamine, 0.44 compared with 0.25 mmol/min), EAA (0.50 compared with 0.21 mmol/min), and BCAA (0.17 compared with 0.06 mmol/min) net fluxes across the hindlimb muscle during 8 h postprandial compared with PS (P < 0.05).

CONCLUSIONS

A diet containing rapidly digested carbohydrate and free amino acids can promote intestinal absorption and net fluxes across hindlimb muscle of amino acids in pigs.

Branched-Chain Amino Acids and Mitochondrial Biogenesis: An Overview and Mechanistic Summary

Branched-chain amino acids (BCAA) are essential in the diet and promote several vital cell responses which may have benefits for health and athletic performance, as well as disease prevention. While BCAA are well-known for their ability to stimulate muscle protein synthesis, their effects on cell energetics are also becoming well-documented, but these receive less attention. In this review, much of the current evidence demonstrating BCAA ability (as individual amino acids or as part of dietary mixtures) to alter regulators of cellular energetics with an emphasis on mitochondrial biogenesis and related signaling is highlighted. Several studies have shown, both in vitro and in vivo, that BCAA (either individual or as a mixture) may promote signaling associated with increased mitochondrial biogenesis including the upregulation of master regulator of mitochondrial biogenesis peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), as well as numerous downstream targets and related function. However, sparse data in humans and the difficulty of controlling variables associated with feeding studies leave the physiological relevance of these findings unclear. Future well-controlled diet studies will be needed to assess if BCAA consumption is associated with increased mitochondrial biogenesis and improved metabolic outcomes in healthy and/or diseased human populations.

Co-ingestion of glutamine and leucine synergistically promotes mTORC1 activation

Leucine (Leu) regulates protein synthesis and degradation via activation of mammalian target of rapamycin complex 1 (mTORC1). Glutamine (Gln) synergistically promotes mTORC1 activation with Leu via glutaminolysis and Leu absorption via an antiporter. However, Gln has also been shown to inhibit mTORC1 activity. To resolve this paradox, we aimed to elucidate the effects of Gln on Leu-mediated mTORC1 activation. We administered Leu, Gln, tryptophan, Leu + Gln, or Leu + tryptophan to mice after 24-h fasting. The mice were then administered puromycin to evaluate protein synthesis and the gastrocnemius muscle was harvested 30 min later. Phosphorylated eukaryotic initiation factor 4E-binding protein 1, 70-kDa ribosomal protein S6 kinase 1, and Unc-51 like kinase 1 levels were the highest in the Leu + Gln group and significantly increased compared with those in the control group; however, Gln alone did not increase the levels of phosphorylated proteins. No difference in glutamate dehydrogenase activity was observed between the groups. Leu concentrations in the gastrocnemius muscle were similar in the Leu-intake groups. Our study highlights a novel mechanism underlying the promotive effect of Gln on Leu-mediated mTORC1 activation, providing insights into the pathway through which amino acids regulate muscle protein metabolism.

Enhancement of BCAT2-Mediated Valine Catabolism Stimulates β-Casein Synthesis via the AMPK-mTOR Signaling Axis in Bovine Mammary Epithelial Cells

Valine, a kind of branched-chain amino acid, plays a regulatory role beyond that of a building block in milk protein synthesis. However, the underlying molecular mechanism through which valine stimulates β-casein synthesis has not been clarified. Therefore, our study aimed to evaluate the effect of valine on β-casein synthesis and shed light into the molecular mechanism using an in vitro model. Results showed that valine supplementation significantly increased β-casein synthesis in bovine mammary epithelial cells (BMECs). Meanwhile, the supplementation of valine resulted in high levels of branched-chain aminotransferase transaminase 2 (BCAT2), TCA-cycle intermediate metabolites, and ATP, AMP-activated protein kinase (AMPK) inhibition, and mammalian target of rapamycin (mTOR) activation. Furthermore, the inhibition of BCAT2 decreased the β-casein synthesis and downregulated the AMPK-mTOR pathway, with similar results observed for AMPK activation. Together, the present data indicate that valine promotes the synthesis of β-casein by affecting the AMPK-mTOR signaling axis and that BCAT2-mediated valine catabolism is the key target.

Effects of dietary L-leucine supplementation on testicular development and semen quality in boars

Sperm and seminal plasma are rich in leucine, and leucine can promote the protein synthesis. This property makes it an interesting amino acid to increase sperm quality of human and livestock spermatogenesis. The goal of this study was to explore the effects of dietary leucine supplementation on testicular development and semen quality in boars from weaning to 10 months of age. 30 pure-bred, weaned Duroc boars (8.0 ± 1.0 kg) were randomly divided into two groups: control group (CON; fed the basal diet) and leucine group (LEU; fed the basal diet supplemented with 1.2% leucine); then, their body weight and testicular volume were recorded every 4 weeks. Testes were collected for histological and genes expression analysis from 150-day-old boars. Semen was collected and analyzed. Amino acids contents of blood plasma, seminal plasma, sperm, and testes were determined. Dietary supplementation with leucine increased the testicular volume and weight of boars, compared with CON. Sperm viability, sperm count per ejaculation, and average curve speed of sperm in leucine-supplemented boars were increased. Furthermore, leucine supplementation increased the blood plasma and seminal plasma leucine concentrations, and enhanced the gene expressions of branch chain amino acid transaminase, protein kinase B, mammalian target of rapamycin (mTOR), and cyclinb1 in the testes. Interestingly, the expressions of the p-mTOR and mTOR proteins in the testes were also upregulated. Thus, dietary leucine supplementation increased leucine absorption and utilization in the testes, promoted testicular development, and improved semen quality of boars, partly through the mTOR signaling pathway.

Zonated leucine sensing by Sestrin-mTORC1 in the liver controls the response to dietary leucine

The mechanistic target of rapamycin complex 1 (mTORC1) kinase controls growth in response to nutrients, including the amino acid leucine. In cultured cells, mTORC1 senses leucine through the leucine-binding Sestrin proteins, but the physiological functions and distribution of Sestrin-mediated leucine sensing in mammals are unknown. We find that mice lacking Sestrin1 and Sestrin2 cannot inhibit mTORC1 upon dietary leucine deprivation and suffer a rapid loss of white adipose tissue (WAT) and muscle. The WAT loss is driven by aberrant mTORC1 activity and fibroblast growth factor 21 (FGF21) production in the liver. Sestrin expression in the liver lobule is zonated, accounting for zone-specific regulation of mTORC1 activity and FGF21 induction by leucine. These results establish the mammalian Sestrins as physiological leucine sensors and reveal a spatial organization to nutrient sensing by the mTORC1 pathway.

Dietary supplementation with branched-chain amino acids enhances milk production by lactating sows and the growth of suckling piglets

Background

Under current dietary regimens, milk production by lactating sows is insufficient to sustain the maximal growth of their piglets. As precursors of glutamate and glutamine as well as substrates and activators of protein synthesis, branched-chain amino acids (BCAAs) have great potential for enhancing milk production by sows.

Methods

Thirty multiparous sows were assigned randomly into one of three groups: control (a corn- and soybean meal-based diet), the basal diet + 1.535% BCAAs; and the basal diet + 3.07% BCAAs. The ratio (g/g) among the supplemental L-isoleucine, L-leucine and L-valine was 1.00:2.56:1.23. Diets were made isonitrogenous by the addition of appropriate amounts of L-alanine. Lactating sows had free access to drinking water and their respective diets. The number of live-born piglets was standardized to 9 per sow at d 0 of lactation (the day of parturition). On d 3, 15 and 29 of lactation, body weights and milk consumption of piglets were measured, and blood samples were obtained from sows and piglets 2 h and 1 h after feeding and nursing, respectively.

Results

Feed intake did not differ among the three groups of sows. Concentrations of asparagine, glutamate, glutamine, citrulline, arginine, proline,  BCAAs, and many other amino acids  were greater (P < 0.05) in the plasma of BCAA-supplemented sows and their piglets than those in the control group. Compared with the control, dietary supplementation with 1.535% and 3.07% BCAAs increased (P < 0.05) concentrations of free and protein-bound BCAAs, glutamate plus glutamine, aspartate plus asparagine, and many other amino acids in milk; milk production by 14% and 21%, respectively; daily weight gains of piglets by 19% and 28%, respectively, while reducing preweaning mortality rates by 50% and 70%, respectively.

Conclusion

Dietary supplementation with up to 3.07% BCAAs enhanced milk production by lactating sows, and the growth and survival of their piglets.

Short communication: Leucine, but not muscle contractions, stimulates protein synthesis in isolated EDL muscles from golden geckos

Resistance exercise and protein ingestion stimulate muscle protein synthesis in mammals and the combination of both stimuli exert an additive effect. However, mechanisms regulating muscle mass may be different in ectothermic vertebrates because these animals are adapted to low energy consumption, short bouts of physical activity, and prolonged periods of inactivity. Here, we investigated the effects of administration of leucine and simulated resistance exercise induced by electrical stimulation (ES) on protein synthesis rate in isolated extensor digitorum longus muscle from golden geckos (Gekko badenii). Muscles were placed in Krebs-Ringer buffer equilibrated with O₂ (97%) and CO₂ (3%) at 30 °C. One muscle from each animal was subjected to one of three interventions: 1) administration of leucine (0.5 mM) at rest, 2) isometric contractions evoked by ES, or 3) a combination of contractions and leucine, while the contralateral muscle served as untreated control. The rate of protein synthesis was measured through pyromycin-labeling. Administration of leucine led to a 2.75 (±1.88)-fold rise in protein synthesis rate in inactive muscles, whereas isometric contractions had no effect (0.67 ± 0.37-fold). The combination of isometric contractions and leucine did not affect protein synthesis rate (1.02 ± 0.34-fold), suggesting that muscle contractions attenuated the positive influence of leucine. Our study identifies leucine as a potent positive regulator of muscle protein synthesis in golden geckos, but also demonstrates that muscle contraction is not. More studies should be conducted in other taxonomic groups of ectothermic vertebrates to identify whether this is a general pattern.

A Mixture of Valine and Isoleucine Restores the Growth of Protein-Restricted Pigs Likely through Improved Gut Development, Hepatic IGF-1 Pathway, and Plasma Metabolomic Profile

Valine (Val) alone or in combination with isoleucine (Ile) improves the growth under severe protein restriction; however, the underlying mechanisms remain unknown. In this study, we assessed whether Val/Ile-induced growth in protein-restricted pigs is associated with changes in gut development, hepatic insulin-like growth factor 1 (IGF-1) production, and blood metabolomics. Forty piglets were assigned to five dietary groups: positive control (PC) with standard protein content; low protein (LP) with very low protein content; and LP supplemented with Val (LPV), Ile (LPI), and Val and Ile (LPVI). LPVI reversed the negative effects of VLP diets on growth and gut morphology. Both LPV and LPVI restored the reduced transcript of IGF-1 while decreasing the transcript of insulin-like growth factor binding protein 1 (IGFBP1) in the liver. LPV and LPVI recovered the reduced plasma Val, glycine, and leucine concentrations, which were positively correlated with improved gut morphology and the hepatic IGF-1 gene expression and negatively correlated with hepatic IGFBP1 mRNA abundance. In conclusion, supplementation with a combination of Val and Ile into the VLP diets restored the decreased growth performance of pigs fed with these diets likely through improved gut development, hepatic IGF-1 expression and bioavailability, and plasma metabolomics profile.

Use of low dosage amino acid blends to prevent stress-related piglet diarrhea

Weaning is a challenging period for piglets associated with reduced feed intake, impairment of gut integrity, and diarrhea. Previous studies demonstrate that supplementation with single functional amino acids (AA) promote piglets' performance due to the improvement of intestinal health. Thus, we hypothesized that a combination of functional AA provided beyond the postulated requirement for growth could facilitate the weaning transition. Ninety piglets, initially stressed after weaning by 100 min overland transport, received a control diet or the same diet supplemented with a low-dosed (0.3%) mixture of AA (AAB-1: L-arginine, L-leucine, L-valine, L-isoleucine, L-cystine; AAB-2: L-arginine, L-leucine, L-valine, L-isoleucine, L-cystine, and L-tryptophan) for 28 days. Fecal consistency was ranked daily, growth performance was assessed weekly. On days 1 and 14 of the trial, blood samples were collected from a subset of 10 piglets per group to assess concentrations of insulin-like growth factor 1. After 28 days of feeding, tissues were obtained from the same piglets to analyze gut morphology and relative mRNA expression of genes related to gut function. Even if the stress response as indicated by rectal temperature was not different between the groups, pigs supplemented with AAB-2 showed firmer feces after weaning and less days with diarrhea compared to control. Furthermore, the jejunal expression of the MUC-2 gene was reduced (P < 0.05) in group AAB-2. Both AA mixtures increased crypt depth in the duodenum. Collectively, the given results indicate that 0.3% extra AA supplementation might alleviate postweaning diarrhea but did not alter growth performance of weanling piglets.

Branched-chain amino acids partially recover the reduced growth of pigs fed with protein-restricted diets through both central and peripheral factors

The objective of this study was to assess the growth efficiency of pigs fed with protein-restricted diets supplemented with branched-chain amino acids (BCAA) and limiting amino acids (LAA) above the recommended levels. Following 2 weeks of adaptation, 48 young barrows were weight matched and randomly assigned to 6 treatments (8 pigs/treatment) for 4 weeks: positive control (PC) with standard protein, negative control (NC) with very low protein containing LAA (i.e., Lys, Met, Thr and Trp) at recommended levels, and NC containing LAA 25% (L25), LAA 50% (L50), LAA+BCAA (i.e., Leu, Ile and Val) 25% (LB25) and LAA+BCAA 50% (LB50) more than recommendations. Feed intake (FI) and body weight (BW) were measured daily and weekly, respectively. At week 6, blood samples were collected, all pigs euthanized and tissue samples collected. The data were analyzed by univariate GLM or mixed procedure (SPSS) and the means were separated using paired Student's t-test followed by Benjamini-Hochberg correction. Relative to PC, NC had decreased FI, BW, unsupplemented plasma essential amino acids, serum insulin-like growth factor-I (IGF-I) and hypothalamic neuropeptide Y (NPY) (P < 0.01). Compared to NC, L25 or L50, LB50 had increased BW and serum IGF-I and decreased plasma serotonin and both LB25 and LB50 had higher FI, plasma BCAA, hypothalamic 5-hydroxytryptamine-receptor 2A and NPY and jejunal 5-hydroxytryptamine-receptor 7 (P < 0.01). Overall, supplementation of protein-restricted diets with increased levels of dietary BCAA partially recovered the negative effects of these diets on growth through improved IGF-I concentration and FI, which was associated with changed expression of serotonin receptors, blood AA and hypothalamic NPY.

Postnatal growth retardation is associated with deteriorated intestinal mucosal barrier function using a porcine model

Individuals with postnatal growth retardation (PGR) are prone to developing chronic diseases. Abnormal development in small intestine is casually implicated in impaired growth. However, the exact mechanism is still implausible. In this present study, PGR piglets (aged 42 days) were employed as a good model to analyze developmental changes in intestinal mucosal barrier function. Our data demonstrated that PGR piglets exhibited impaired jejunal and ileal epithelial villous morphology and permeability, accompanied by decreased cell proliferation ability and increased apoptosis rate. In addition, the expression of tight junction proteins (ZO-1, claudin 1, and occludin) and E-cadherin was markedly inhibited by PGR. The expression of P-glycoprotein was significantly reduced in PGR piglets, as well as decreased activity of lysozyme. Moreover, the mRNA abundance and content of inflammatory cytokines were significantly increased in the intestinal mucosa and plasma of PGR piglets, respectively. PGR also contributed to lower level of sIgA, and higher level of CD68-positive rate, β-defensins, and protein expression involved p38 MAPK/NF-κB pathway. Furthermore, PGR altered the intestinal microbial community such as decreased genus Alloprevotella and Oscillospira abundances, and led to lower microbial-derived butyrate production, which may be potential targets for treatment. Collectively, our findings indicated that the intestinal mucosal barrier function of PGR piglets could develop the nutritional intervention strategies in prevention and treatment of the intestinal mucosal barrier dysfunction in piglets and humans.

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.

Bacteriophage as an Alternative to Antibiotics Promotes Growth Performance by Regulating Intestinal Inflammation, Intestinal Barrier Function and Gut Microbiota in Weaned Piglets

This study aimed to investigate the effects of dietary bacteriophage supplementation on growth performance, intestinal morphology, barrier function, and intestinal microbiota of weaned piglets fed antibiotic-free diet. A total of 120 weaned piglets were allotted to four dietary treatments with five pens/treatment and six piglets/pen in a 21-d feeding trial. The control diet was supplemented with 25 mg/kg quinocetone and 11.25 mg/kg aureomycin in the basal diet, while the three treatment diets were supplemented with 200, 400, or 600 mg/kg bacteriophage in the basal diet, respectively. There was no difference for growth performance and all measured indices of serum and intestinal tissues between 200 mg/kg bacteriophage group and the control group with antibiotics (P > 0.05). More importantly, compared with the control diet, dietary 400 mg/kg bacteriophage inclusion increased average daily gain and average daily feed intake, and decreased feed/gain ratio and diarrhea incidence of weaned piglets (P < 0.05). Also, piglets fed 400 mg/kg bacteriophage had elevated villi height (VH) in jejunum and ileum, reduced crypt depth (CD) in jejunum and ileum, and elevated VH/CD ratio in duodenum, jejunum and ileum (P < 0.05). Compared to the control group, piglets fed 400 mg/kg bacteriophage had lower interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), and higher interleukin-10 (IL-10) concentration in serum, and higher secretory immunoglobulin A (sIgA), intestinal trefoil factor (ITF), and tumor growth factor-alpha (TGF-α) content in the ileal mucosa (P < 0.05). Besides, dietary addition with 400 mg/kg bacteriophage decreased the D-lactate concentration and diamine oxidase (DAO) activity in serum, and increased the relative mRNA expression of ZO-1, Claudin-1, Occludin, TLR2, TLR4, and TLR9, as well as the relative protein expression of Occludin in the jejunum (P < 0.05). However, the growth performance and all analyzed parameters in serum and intestinal tissues were not further improved when piglets fed 600 vs. 400 mg/kg bacteriophage (P > 0.05). MiSeq sequencing analysis showed that bacteriophage regulated the microbial composition in caecum digesta, as indicated by higher observed_species, Chao1, and ACE richness indices, as well as changes in the relative abundance of Firmicutes, Bacteroidetes, and Tenericutes (P < 0.05). Collectively, 400 mg/kg bacteriophage can be used as an antibiotics alternative for promoting the growth of weaned piglets. The underlying mechanism is associated with a positive effect of bacteriophage on intestinal inflammation, intestinal barrier function and gut microbiota in weaned piglets.

Management and Feeding Strategies in Early Life to Increase Piglet Performance and Welfare around Weaning: A Review

The performance of piglets in nurseries may vary depending on body weight, age at weaning, management, and pathogenic load in the pig facilities. The early events in a pig's life are very important and may have long lasting consequences, since growth lag involves a significant cost to the system due to reduced market weights and increased barn occupancy. The present review evidences that there are several strategies that can be used to improve the performance and welfare of pigs at weaning. A complex set of early management and dietary strategies have been explored in sows and suckling piglets for achieving optimum and efficient growth of piglets after weaning. The management strategies studied to improve development and animal welfare include: (1) improving sow housing during gestation, (2) reducing pain during farrowing, (3) facilitating an early and sufficient colostrum intake, (4) promoting an early social interaction between litters, and (5) providing complementary feed during lactation. Dietary strategies for sows and suckling piglets aim to: (1) enhance fetal growth (arginine, folate, betaine, vitamin B12, carnitine, chromium, and zinc), (2) increase colostrum and milk production (DL-methionine, DL-2-hydroxy-4-methylthiobutanoic acid, arginine, L-carnitine, tryptophan, valine, vitamin E, and phytogenic actives), (3) modulate sows' oxidative and inflammation status (polyunsaturated fatty acids, vitamin E, selenium, phytogenic actives, and spray dried plasma), (4) allow early microbial colonization (probiotics), or (5) supply conditionally essential nutrients (nucleotides, glutamate, glutamine, threonine, and tryptophan).

The role of liver metabolism in compensatory-growth piglets induced by protein restriction and subsequent protein realimentation

The aim of this work was to study the role of hepatic metabolism of compensatory growth in piglets induced by protein restriction and subsequent protein realimentation. Thirty-six weaned piglets were randomly distributed in a control group and a treatment group. The control group piglets were fed with a normal protein level diet (18.83% CP) for the entire experimental period (day 1-28). The treatment group piglets were fed with a protein-restriction diet (13.05% CP) for day 1 to day 14, and the diet was restored to normal protein level diet for day 15 to day 28. RNA-seq is used to analyze samples of liver metabolism on day 14 and day 28, respectively. Hepatic RNA-sequencing analysis revealed that some KEGG signaling pathways involved in glycolipid metabolism (eg, "AMPK signaling pathway," "insulin signaling pathway," and "glycolysis or gluconeogenesis") were significantly enriched on day 14 and day 28. On day 14, protein restriction promoted hepatic lipogenesis by increasing the genes expression level of ACACA, FASN, GAPM, and SREBP1C, decreasing protein phosphorylation levels of AMPKɑ and ACC in AMPK signaling pathway. In contrast, on day 28, protein realimentation promoted hepatic gluconeogenesis by increasing the concentration of G6Pase and PEPCK, decreasing protein phosphorylation levels of IRS1, Akt, and FoXO1 in insulin signaling pathway. In addition, protein realimentation activated the GH-IGF1 axis between the liver and skeletal muscle. Overall, these findings revealed the importance of liver metabolism in achieving compensatory growth.

Prenatal alcohol exposure and maternal glutamine supplementation alter the mTOR signaling pathway in ovine fetal cerebellum and skeletal muscle

Prenatal alcohol exposure causes fetal neurodevelopmental damage and growth restriction. Among regions of the brain, the cerebellum is the most vulnerable to developmental alcohol exposure. Despite vast research in the field, there is still a need to identify specific mechanisms by which alcohol causes this damage in order to design effective therapeutic interventions. The mammalian target of rapamycin (mTOR) is known to be associated with axonal regeneration, dendritic arborization, synaptic plasticity, cellular growth, autophagy, and many other cellular processes. Glutamine and glutamine-related amino acids play a key role in fetal development and are known to alter the mTOR pathway; recent research has shown that disturbances in their bioavailability and signaling pathways may mediate adverse effects of prenatal alcohol exposure. This study investigated the role of the mTOR signaling pathway in the fetal cerebellum and skeletal muscle after third trimester-equivalent prenatal alcohol exposure and maternal l-glutamine (GLN) supplementation using a sheep model. Fetal cerebella and skeletal muscles were sampled for Western blot analysis of mTOR and its downstream targets S6 kinase and eukaryotic initiation factor 4E-bindin protein (4E-BP1). The expression of cerebellar phosphorylated mTOR relative to the total mTOR was elevated in the alcohol+GLN group compared to the saline and GLN groups. Alcohol exposure increased the ratio of phosphorylated S6K to total S6K in fetal cerebellum, and no significant effect of GLN supplementation was observed. On contrary, maternal GLN supplementation reduced the activation of mTOR and S6K in fetal skeletal muscle, possibly to make GLN and other amino acids available for use by other organs. These findings suggest prenatal alcohol exposure and maternal GLN supplementation during the third trimester-equivalent alter the mTOR signaling cascade, which plays a possible key role in alcohol-induced developmental damage.

Effects of dietary leucine levels on intestinal antioxidant status and immune response for juvenile golden pompano (Trachinotus ovatus) involved in Nrf2 and NF-κB signaling pathway

The aim of the study was to evaluate the effects of dietary leucine level on growth performance, intestinal antioxidant status and immune response involved in Nrf2 and NF-κB signaling pathway in juvenile golden pompano (Trachinotus ovatus). A total of 450 juvenile golden pompano (9.15 ± 0.04 g) were fed three isonitrogenous diets with graded leucine levels [1.25% (control), 2.77% and 5.84%] for 8 weeks. The results showed that, compared with the control group, the WG was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05), and the 5.84% dietary leucine group had a tendency to increase. Compared to control group, 5.84% dietary leucine group significantly decreased the moisture and ash contents of whole body (P < 0.05), meanwhile, 2.77% dietary leucine group significantly decreased moisture content of whole body, but significantly improved the whole body crude lipid content (P < 0.05). Compared with the control group, the ALP level was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). Inversely, the AST and ALT activities were significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). Compared with the control group, GPx, T-AOC, SOD activities in group of 2.77% dietary arginine level were significantly increased (P < 0.05). However, MDA level showed a reverse trend, which was significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). 2.77% dietary leucine levels significantly increased the relative expressions of Nrf2, HO-1, Cu/Zn-SOD, Mn-SOD and CAT (P < 0.05). In contrast, the relative expression of Keap1 showed a converse trend. Compared with the control group, the relative expressions of NF-κB, TNF-α and IL1-β were significantly lowered in fish fed with 2.77% of dietary leucine (P < 0.05). Additionally, 2.77% dietary leucine level significantly improved the relative expressions of TGF-β and IL-10 (P < 0.05). The 2.77% dietary leucine level significantly increased the muscular thickness compared with 5.84% dietary leucine level (P < 0.05). Furthermore, compared with the control group, the villus height and goblet cell counts were significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). These results indicated that the optimum dietary leucine plays an important role in promoting growth, enhancing antioxidant and immunity to maintain the intestinal health status of juvenile golden pompano.

Progress towards pig nutrition in the last 27 years

Over the last 27 years (1990-2017), based on the revolutionary progresses of basic nutrition research, novel methods and techniques have been developed which bring a profound technological revolution to pig production from free-range system to intensive farming all over the world. Basic theoretical innovations and feed production studies have provided vital advancements in pig nutrition by developing formula feed, utilizing balanced diets, determining feed energy value, dividing pig physiological stages, enhancing gut health, and improving feed processing technique. Formula feed is the primary contributor of the rise of the mechanized farming industry, and meets comprehensive nutritional needs of the pig. The focuses of the development of a balanced diet by optimizing nutrient levels are the amino acids balance, the balance between amino acids and energy, the balance between calcium and phosphorus. Multiple-site-production and targeted feeding program have been applied extensively. Early weaning of piglets improves production efficiency, but piglets that have not yet fully developed their intestine are prone to diarrhea. Therefore, intestinal health has received special attention in recent years. Feed processing technologies, such as granulation, puffing, fermentation and enzymatic hydrolysis, can improve the utilization of feed nutrients and reduce production cost. However, increasing a sow's potential for production, seeking alternatives to antibiotics, reducing drug treatment in piglets, developing functional additives and improving meat quality remain future challenges. Herein, we outline the important progresses of pig nutrition in the past 27 years, which will shed light on the basic nutrition rules of pig production, and help to push forward its future development. © 2018 Society of Chemical Industry.

Effect of antibiotic-free, low-protein diets with specific amino acid compositions on growth and intestinal flora in weaned pigs

This study investigated the effects of modulation of the amino acid profile on growth performance and gut health in weaned pigs fed an antibiotic-free, low-protein diet. In experiment 1, 5 treatments were included: a control diet with antibiotics; a low-protein diet with antibiotics; a low-protein diet without antibiotics (LP); a LP diet with 10% more dietary essential amino acids (LP110); and an LP110 diet with 12% more dietary Met + Cys, Thr and Trp. The intestinal digestive enzyme activity and morphology were improved with the increase in dietary essential amino acid levels, while the growth performance was decreased, indicating that the dietary amino acid level was too high. In experiment 2, all 5 treatments of experiment 1 were included, plus a LP diet with 5% more dietary essential amino acids (LP105) and an LP105 diet with 6% more dietary Met + Cys, Thr and Trp. The LP105 treatment showed optimal feed efficiency, a reduced plasma endotoxin concentration, and an increased fecal lactate concentration and increased abundances of Prevotellaceae and Roseburia bacteria. Our results demonstrate that the optimal amino acid profile in an antibiotic-free, low-protein diet can efficiently improve growth performance and gut health and modulate the fecal microbial structure in weaned pigs.

Effect of very low-protein diets supplemented with branched-chain amino acids on energy balance, plasma metabolomics and fecal microbiome of pigs

Feeding pigs with very-low protein (VLP) diets while supplemented with limiting amino acids (AA) results in decreased growth. The objective of this study was to determine if supplementing VLP diets with branched-chain AA (BCAA) would reverse the negative effects of these diets on growth and whether this is associated with alterations in energy balance, blood metabolomics and fecal microbiota composition. Twenty-four nursery pigs were weight-matched, individually housed and allotted into following treatments (n = 8/group): control (CON), low protein (LP) and LP supplemented with BCAA (LP + BCAA) for 4 weeks. Relative to CON, pigs fed with LP had lower feed intake (FI) and body weight (BW) throughout the study, but those fed with LP + BCAA improved overall FI computed for 4 weeks, tended to increase the overall average daily gain, delayed the FI and BW depression for ~ 2 weeks and had transiently higher energy expenditure. Feeding pigs with LP + BCAA impacted the phenylalanine and protein metabolism and fatty acids synthesis pathways. Compared to CON, the LP + BCAA group had higher abundance of Paludibacteraceae and Synergistaceae and reduced populations of Streptococcaceae, Oxyphotobacteria_unclassified, Pseudomonadaceae and Shewanellaceae in their feces. Thus, supplementing VLP diets with BCAA temporarily annuls the adverse effects of these diets on growth, which is linked with alterations in energy balance and metabolic and gut microbiome profile.

Postnatal growth retardation is associated with intestinal mucosa mitochondrial dysfunction and aberrant energy status in piglets

Individuals with postnatal growth retardation (PGR) are prone to developing chronic disease. Abnormal development in small intestine is casually implicated in impaired growth performance. However, the exact mechanism is still unknown. In this present study, PGR piglets (aged 42 days) were employed as a good model to analyse changes in nutrient absorption and energy metabolism in the intestinal mucosa. The results showed lower serum concentrations of free amino acids, and lipid metabolites in PGR piglets, which were in accordance with the down‐regulated mRNA expressions involved in fatty acid and amino acid transporters in the jejunal and ileal mucosa. The decreased activities of digestive enzymes and the marked swelling in mitochondria were also observed in the PGR piglets. In addition, it was found that lower ATP production, higher AMP/ATP ratio, deteriorated mitochondrial complex III and ATP synthase, and decreased manganese superoxide dismutase activity in the intestinal mucosa of PGR piglets. Furthermore, altered gene expression involved in energy metabolism, accompanied by decreases in the protein abundance of SIRT1, PGC‐1α and PPARγ, as well as phosphorylations of AMPKα, mTOR, P70S6K and 4E‐BP1 were observed in intestinal mucosa of PGR piglets. In conclusion, decreased capability of nutrient absorption, mitochondrial dysfunction, and aberrant energy status in the jejunal and ileal mucosa may contribute to PGR piglets.

A selectively suppressing amino acid transporter: Sodium-coupled neutral amino acid transporter 2 inhibits cell growth and mammalian target of rapamycin complex 1 pathway in skeletal muscle cells

Sodium-coupled neutral amino acid transporter 2 (SNAT2), also known as solute carrier family 38 member 2 (SLC38A2), is expressed in the skeletal muscle. Our research previously indicated that SNAT2 mRNA expression level in the skeletal muscle was modulated by genotype and dietary protein. The aim of this study was to investigate the key role of the amino acid transporter SNAT2 in muscle cell growth, differentiation, and related signaling pathways via SNAT2 suppression using the inhibitor α-methylaminoisobutyric acid (MeAIB). The results showed that SNAT2 suppression down-regulated both the mRNA and protein expression levels of SNAT2 in C2C12 cells, inhibited cell viability and differentiation of the cell, and regulated the cell distribution in G0/G1 and S phases (P < 0.05). Meanwhile, most of the intercellular amino acid content of the cells after MeAIB co-culturing was significantly lower (P < 0.05). Furthermore, the mRNA expression levels of system L amino acid transporter 1 (LAT1), silent information regulator 1, and peroxisome proliferator-activated receptor-gamma co-activator 1 alpha, as well as the protein expression levels of amino acid transporters LAT1 and vacuolar protein sorting 34, were all down-regulated. The phosphorylated protein expression levels of mammalian target of rapamycin (mTOR), regulatory-associated protein of mTOR, 4E binding protein 1, and ribosomal protein S6 kinase 1 after MeAIB treatment were also significantly down-regulated (P < 0.05), which could contribute to the importance of SNAT2 in amino acid transportation and skeletal muscle cell sensing. In conclusion, SNAT2 suppression inhibited C2C12 cell growth and differentiation, as well as the availability of free amino acids. Although the mTOR complex 1 signaling pathway was found to be involved, its response to different nutrients requires further study.

Effects of vitamin B6 on growth, diarrhea rate, intestinal morphology, function, and inflammatory factors expression in a high-protein diet fed to weaned piglets1

Vitamin B6 (VB6) is an important coenzyme factor which participates in many metabolic reactions, especially amino acid metabolism. There are few reports on how VB6 mediates weaned piglet intestinal health. This study purposed to investigate dietary VB6 effects on growth, diarrhea rates, and intestinal morphology and function in weaned piglets fed a high-crude protein (22% CP) diet. Eighteen 21-d-old weaned [(Yorkshire × Landrace) × Duroc] piglets with body weights of 7.03 ± 0.15 (means ± SEM) kg were randomly assigned into 3 VB6-containing dietary treatments. Vitamin B6 content was: 0, 4, and 7 mg/kg, respectively. The feeding period lasted 14 d. The results showed that no significant difference existed for the growth performance. The 7 mg/kg VB6 group had a tendency to decrease diarrhea rate (P = 0.065). Blood biochemical parameters analysis demonstrated that total protein, cholesterol, and high-density lipoprotein significantly increased in the 7 mg/kg VB6 group (P < 0.05). In the jejunum, no significant differences were detected for villus height, villus width, crypt depth, villus height and crypt depth ratios, and positive Ki67 counts and the mRNA expression of inflammatory cytokines. Vitamin B6 significantly increased the mRNA expression of SLC6A19 and SLC6A20 (P < 0.05) and decreased the mRNA expression of SLC36A1 (P < 0.05). In the ileum, VB6 significantly increased villus height and villus width (P < 0.05) while decreased positive Ki67 cell counts for 7 mg/kg VB6 group (P < 0.05). Vitamin B6 had significantly increased the mRNA expression of interleukin-1β, tumor necrosis factor-α,cyclo-oxygen-ase-2, and transforming growth factor-β (P < 0.05). Vitamin B6 also had significantly increased mRNA expression of SLC6A19, SLC7A6, SLC7A7, and SLC36A1 (P < 0.05). These findings suggest that dietary supplementation with VB6 may affect the intestinal morphology and absorption and metabolism of protein in weaned piglets fed a high-protein diet by altering the expression of intestinal inflammatory cytokines and amino acid transporters.

The influence of dietary leucine above recommendations and fixed ratios to isoleucine and valine on muscle protein synthesis and degradation pathways in broilers

This study investigated the hypothesis that dietary supplementation of leucine (Leu) above actual recommendations activates protein synthesis and inhibits protein degradation pathways on the molecular level and supports higher muscle growth in broilers. Day-old male Cobb-500 broilers (n = 180) were allotted to 3 groups and phase-fed 3 different corn-wheat-soybean meal-based basal diets during periods 1 to 10, 11 to 21, and 22 to 35 D. The control group (L0) received the basal diet which met the broiler's requirements of nutrients and amino acids for maintenance and growth. Groups L1 and L2 received basal diets supplemented with Leu to exceed recommendations by 35 and 60%, respectively, and isoleucine (Ile) and valine (Val) were supplemented to keep Leu: Ile and Leu: Val ratios fixed. Samples of liver and breast muscle and pancreas were collected on days 10, 21, and 35. The gene expression and abundance of total and phosphorylated proteins involved in the mammalian target of rapamycin pathway of protein synthesis, in the ubiquitin-proteasome pathway and autophagy-lysosomal pathway of protein degradation, in the general control nonderepressible 2/eukaryotic translation initiation factor 2A pathway involved in the inhibition of protein synthesis, and in the myostatin-Smad2/3 pathway involved in myogenesis were evaluated in the muscle, as well as expression of genes involved in the growth hormone axis. Growth performance, feed intake, the feed conversion ratio, and carcass weights did not differ between the 3 groups (P > 0.05). Plasma concentrations of Leu, Ile, and Val and of their keto acids, and the activity of the branched-chain α-keto acid dehydrogenase in the pancreas increased dose dependently with increasing dietary Leu concentrations. In the breast muscle, relative mRNA abundances of genes and phosphorylation of selected proteins involved in all investigated pathways were largely uninfluenced by dietary Leu supplementation (P > 0.05). In summary, these data indicate that excess dietary Leu concentrations do not influence protein synthesis or degradation pathways, and subsequently do not increase muscle growth in broilers at fixed ratios to Ile and Val.

Metabolome and proteome changes in skeletal muscle and blood of pre-weaning calves fed leucine and threonine supplemented diets

In pre-weaning calves, both leucine and threonine play important roles in growth and muscle metabolism. In this study, metabolomics, proteomics and clinical chemistry were used to assess the effects of leucine and threonine supplementation added to milk replacer on 14 newborn Holstein male calves: 7 were fed a control diet (Ctrl) and 7 were fed the Ctrl diet supplemented with 0.3% leucine and 0.3% threonine (LT) from 5.6 days of age to 53.6 days. At this time, blood and semitendinosus muscle biopsies were collected for analysis. Integrated metabolomics and proteomics showed that branched-chain amino acids (BCAA) degradation and mitochondrial oxidative metabolism (citrate cycle and respiratory chain) were the main activated pathways in muscle because of the supplementation. BCAA derivatives and metabolites related to lipid mobilization showed the major changes. The deleterious effects of activated oxidative phosphorylation were balanced by the upregulation of antioxidant proteins. An increase in protein synthesis was indicated by elevated aminoacyl-tRNA biosynthesis and increased S6 ribosomal protein phosphorylation in skeletal muscle. In conclusion, LT group showed greater BCAA availability and mitochondrial oxidative activity; as the muscle cells undergo greater aerobic metabolism, antioxidant defenses were activated to compensate for possible cell damage. Data are available via ProteomeXchange (PXD016098). SIGNIFICANCE: Leucine and threonine are essential amino acids for the pre-weaning calf, being of high importance for growth. In this study, we found that leucine and threonine supplementation of milk replacer to feed pre-weaning calves led to differences in the proteome, metabolome and clinical chemistry analytes in skeletal muscle and plasma, albeit no differences in productive performance were recorded. This study extends our understanding on the metabolism in dairy calves and helps optimizing their nutritional status.

The coordination of dietary valine and isoleucine on water holding capacity, pH value and protein solubility of fresh meat in finishing pigs

To investigate coordination of dietary levels of valine (Val) and isoleucine (Ile) on carcass traits and meat quality in pigs, 72 of 73.8 ± 1.6 kg crossbred barrows were randomly divided into a 2 (0.31% vs. 0.65% standard ileum digestible (SID) Val) × 2 (0.25% vs. 0.53% SID Ile) factorial arrangement. As a result, high dietary valine decreased myosin heavy-chain (MyHC)-I mRNA expression, pH_{24 h} value, bound water amount (T₂₁ peak area ratio), sarcoplasmic protein solubility and water holding capacity (WHC) of meat (P < .05). Meanwhile, high dietary isoleucine increased pH_{24 h} value, sarcomere length (P < .05) and tend to decrease drip loss (P = .07). The significant interactions between valine and isoleucine were observed on backfat thickness, water distribution forms and myofibrillar protein solubility (P < .05) of pork. High valine diets undermined WHC of meat probably through decreasing pH_{24 h} value and sarcoplasmic protein solubility considering their significant correlations with drip loss.

Maternal Nutrient Restriction and Skeletal Muscle Development: Consequences for Postnatal Health

Severe undernutrition and famine continue to be a worldwide concern, as cases have been increasing in the past 5 years, particularly in developing countries. The occurrence of nutrient restriction (NR) during pregnancy affects fetal growth, leading to small for gestational age (SGA) or intrauterine growth restricted (IUGR) offspring. During adulthood, SGA and IUGR offspring are at a higher risk for the development of metabolic syndrome. Skeletal muscle is particularly sensitive to prenatal NR. This tissue plays an essential role in oxidation and glucose metabolism because roughly 80% of insulin-mediated glucose uptake occurs in muscle, and it represents around 40% of body weight. Alterations in myofiber number, hypertrophy and myofiber type composition, decreased protein synthesis, lower mitochondrial content and activity of oxidative enzymes, and increased accumulation of intramuscular triglycerides are among the described programming effects of maternal NR on skeletal muscle. Together, these features would add to a phenotype that is prone to insulin resistance, type 2 diabetes, obesity, and metabolic syndrome. Insights from diverse animal models (i.e. ovine, swine, and rodent) have provided valuable information regarding the molecular mechanisms behind those altered developmental pathways. Understanding those molecular signatures supports the development of efficient treatments to counteract the effects of maternal NR on skeletal muscle, and its negative implications for postnatal health.

Dietary Leucine Supplementation Restores Serum Glucose Levels, and Modifying Hepatic Gene Expression Related to the Insulin Signal Pathway in IUGR Piglets

Simple Summary

Intrauterine malnutrition may compromise the size and structure of fetal organs and tissues, which leads to lower birth weight and a slower rate of growth after weaning. Intrauterine growth restriction/retardation (IUGR) impairs pancreas function, resulting in the decreased glucose levels in serum. Leucine, one of branched chain amino acids, is an essential amino acid and the substrate of protein synthesis. Leucine also acts as a major regulator of hormone signal transduction, like insulin. Dietary branched chain amino acids or leucine have beneficial effects on the glucose metabolism and glycogen synthesis of muscle. Leucine supplementation improves the insulin sensitivity in liver and muscle and then influences the systemic glucose homeostasis. However, it is still unclear whether leucine supplementation would alter insulin sensitivity in IUGR neonatal piglets. Our results showed that dietary leucine supplementation restored serum glucose concentrations, increased insulin and creatinine concentrations, and enhanced protein kinase adenosine monophosphate-activated γ 3-subunit and glucose transporter type 2 expression. These findings suggest that leucine might play a positive role in hepatic lipid metabolism and glucose metabolism in IUGR.

Abstract

This study aimed to investigate the effects of leucine with different levels on the insulin resistance in intrauterine growth restriction/retardation (IUGR) piglets. Thirty-two weaned piglets were arranged in a 2 × 2 factorial design and four treatments (n = 8) were as follow: (1) normal weaned piglets fed a basal diet (CONT), (2) IUGR weaned piglets fed a basal diet (IUGR), (3) normal weaned piglets fed a basal diet with the addition of 0.35% l-leucine (C-LEU), and (4) IUGR fed a basal diet with the addition of 0.35% l-leucine (I-LEU) for a 21-days trial. The results showed that compared to the IUGR group, the I-LEU group had higher final body weight and body weight gain, higher serum glucose concentrations, and higher serum insulin concentrations (p < 0.05). The gene expression of phosphatidylinositol 3-kinase p110 gamma, protein kinase adenosine monophosphate-activated γ 3-subunit, glycogen synthase kinase-3 alpha, and glucose transporter type 2 were increased in the I-LEU group as compared to the IUGR group (p < 0.05). It was concluded that dietary leucine supplementation restored serum glucose concentrations, increased insulin and creatinine concentrations, and enhanced protein kinase adenosine monophosphate-activated γ 3-subunit and glucose transporter type 2 expression, suggesting that leucine might play a positive role in hepatic lipid metabolism and glucose metabolism in IUGR.

Modeling nutritional and performance factors that influence the efficiency of weight gain in relation to excreted nitrogen in weaning piglets

One of the most debated topics in pig production is the need to study, understand and change the production system in order to improve nutrient efficiency, becoming more environmentally friendly. The nitrogen excretion has highly deleterious effects on the environment, and it is necessary to develop tools that help to reduce the excretion of this compound without compromising productivity. Therefore, two models were generated to estimate the efficiency of weight gain in relation to excreted nitrogen in post-weaning piglets. Data for testing these models were obtained from previous master and PhD studies carried out at the Federal University of Rio Grande do Sul, Animal Science Laboratory using piglets in the post-weaning phase with results for performance and digestibility. The database that was constructed was composed of raw data from 10 studies carried out between 2000 and 2016, on a total of 726 piglets weaned at ages between 17 and 28 days, and to which 62 different treatments were applied. An exploratory analysis of the data was done by evaluating scatter plots and histograms, and variables representing different treatments were used in a stepwise multiple linear regression analysis, with the F-test used as the selection criterion. Two models were generated that either considered the nitrogen retained or not, to estimate the ratio between weight gain and excreted nitrogen using generalized linear model procedure. The authors analyzed the behavior of each variable to evaluate whether the equation generated was biologically coherent. Weight gain, dry matter intake, nitrogen intake, metabolizable energy intake, retained nitrogen and urinary nitrogen were all significant (P<0.001) variables in model I, and in model II the variable fecal nitrogen was also included. The models had high coefficients of determination (R2 of model I and II were 0.9013 and 0.8271, respectively), and the nitrogen ingested variable was the one that most strongly influenced growth efficiency. When the retained nitrogen variable was removed from the model, there was a reduction in the fit of the equations. It was possible to conclude that both of the two models generated could be applied and the amount of nitrogen ingested had the greatest influence on growth efficiency related to nitrogen excretion.

Dietary Branched-Chain Amino Acids Regulate Food Intake Partly through Intestinal and Hypothalamic Amino Acid Receptors in Piglets

Strategies to increase feed intake are of great importance for producing more meat in swine production. Intestinal and hypothalamic amino acid receptors are found to largely participate in feed intake regulation. The purpose of the current research is to study the function of branched-chain amino acid (BCAA) supplementation in the regulation of feed intake through sensors that can detect amino acids in piglets. Twenty-four piglets were assigned one of four treatments and fed one of the experimental diets for either a short period (Expt. 1) or a long period (Expt. 2): a normal protein diet (NP, 20.04% CP), a reduced-protein diet (RP, 17.05% CP), or a reduced-protein test diet supplemented with one of two doses of BCAAs (BCAA1, supplemented with 0.13% l-isoleucine, 0.09% l-leucine, and 0.23% l-valine; BCAA2, supplemented with the 150% standardized ileal digestibility BCAA requirement, as recommended by the National Research Council (2012)). In Expt. 1, no differences were observed in the feed intake among piglets fed different diets ( P > 0.05). In Expt. 2, compared with the RP group, the feed intake of piglets was significantly increased after sufficient BCAAs were supplemented in the BCAA1 group, which was associated with decreased cholecystokinin secretion ( P < 0.05), down-regulated expression of type-1 taste receptors 1/3 (T1R1/T1R3) in the intestine, as well as increased expression of pro-opiomelanocortin, activated general control nonderepressible 2 (GCN2), and eukaryotic initiation factor 2α (eIF2α) in the hypothalamus ( P < 0.05). However, the feed intake was decreased for unknown reasons when the piglets were fed a BCAA over-supplemented diet. Our study confirmed that a BCAA-deficient diet inhibited feed intake through two potential ways: regulating the amino acid T1R1/T1R3 receptor in the intestine or activating GCN2/eIF2α pathways in the hypothalamus.

N-Carbamylglutamate and l-Arginine Promote Intestinal Absorption of Amino Acids by Regulating the mTOR Signaling Pathway and Amino Acid and Peptide Transporters in Suckling Lambs with Intrauterine Growth Restriction

BACKGROUND

Previous studies have revealed that dietary N-carbamylglutamate (NCG) and l-arginine (Arg) improve intestinal integrity, oxidative state, and immune function in Hu suckling lambs with intrauterine growth restriction (IUGR). Whether these treatments alter intestinal nutrient absorption is unknown.

OBJECTIVE

The aim of this study was to determine the influence of dietary NCG and Arg treatment during the suckling period on intestinal amino acid (AA) absorption, alterations in the mechanistic target of rapamycin (mTOR) signaling pathway, and the abundance of AA and peptide transporters in IUGR lambs.

METHODS

On day 7 after birth, 48 newborn Hu lambs were selected from a cohort of 424 twin lambs. Normal-birth-weight and IUGR Hu lambs were allocated randomly (n = 12/group) to a control (4.09 ± 0.12 kg), IUGR (3.52 ± 0.09 kg), IUGR + 0.1% NCG (3.49 ± 0.11 kg), or IUGR + 1% Arg (3.53 ± 0.10 kg).

RESULTS

At day 28, compared with the IUGR group, the IUGR groups receiving NCG and Arg had 7.4% and 7.2% greater (P < 0.05) body weight, respectively. Compared with the IUGR group, the serum concentration of insulin was greater (P < 0.05) and the cortisol was lower (P < 0.05) in the IUGR groups receiving NCG and Arg. Compared with the IUGR group, the IUGR groups receiving NCG and Arg had 13.2%-62.6% greater (P < 0.05) serum concentrations of arginine, cysteine, isoleucine, and proline. Dietary NCG or Arg to IUGR lambs resulted in greater protein abundance (P < 0.05) of peptide transporter 1 (41.9% or 38.2%) in the ileum compared with the unsupplemented IUGR lambs, respectively. Furthermore, dietary NCG or Arg treatment normalized the IUGR-induced variation (P < 0.05) in the ileal ratio of phosphorylated mTOR to total mTOR protein.

CONCLUSION

Both NCG and Arg can help mitigate the negative effect of IUGR on nutrient absorption in neonatal lambs.

Effects of leucine supplementation on muscle protein synthesis and degradation pathways in broilers at constant dietary concentrations of isoleucine and valine

The present study investigated the hypothesis that dietary concentrations of leucine (Leu) in excess of the breeder´s recommendations activates protein synthesis and decreases protein degradation in muscle of broilers. Day-old male Ross 308 broilers (n = 450) were phase-fed corn-soybean meal-based diets during starter (d 1-10), grower (d 11-22), and finisher (d 23-34) period. The basal diets fed to the control group (L0) met the broilers' requirements for nutrients and amino acids, and contained Leu, Leu:isoleucine (Ile) and Leu:valine (Val) ratios, close to those recommended by the breeder (Leu:Ile: 100:54, 100:52, 100:51; Leu:Val 100:64, 100:61, 100:58; in starter, grower and finisher diet, resp.). Basal diets were supplemented with Leu to exceed the breeder's recommendations by 35% (group L35) and 60% (group L60). Growth performance during 34 d, and carcass weights, and breast and thigh muscle weights on d 34 were similar among groups. Hepatic and muscle mRNA levels of genes involved in the somatotropic axis [growth hormone receptor, insulin-like growth factor (IGF)-1, IGF binding protein 2, IGF receptor] on d 34 were not influenced by Leu. In the breast muscle, relative mRNA abundances of genes involved in the mammalian target of rapamycin (mTOR) pathway of protein synthesis (mTOR, ribosomal p70 S6 kinase) and the ubiquitin-proteasome pathway of protein degradation (F-box only protein 32, Forkhead box protein O1, Muscle RING-finger protein-1) on d 34 were largely similar among groups. Likewise, relative phosphorylation and thus activation of mTOR and ribosomal protein S6 involved in the mTOR pathway, and of eukaryotic translation initiation factor 2A (eIF2a) involved in the general control nonderepressible 2 (GCN2)/eIF2a pathway of protein synthesis inhibition, were not influenced. These data indicate that dietary Leu concentrations exceeding the broiler´s requirements up to 60% neither influence protein synthesis nor degradation pathways nor muscle growth in growing broilers.

Eccentric resistance training and β-hydroxy-β-methylbutyrate free acid affects muscle PGC-1α expression and serum irisin, nesfatin-1 and resistin in rats

The hypothalamus controls metabolism and feeding behaviour via several signals with other tissues. Exercise and supplements can change hypothalamic signalling pathways, so the present study investigated the influence of eccentric resistance training and β-hydroxy-β-methylbutyrate free acid supplementation on PGC-1α expression, serum irisin, nesfatin-1 and resistin concentrations. Thirty-two male rats (8 weeks old, 200±17 g body mass) were randomly allocated to control, β-hydroxy-β-methylbutyrate free acid supplementation (HMB), eccentric resistance training (ERT), and β-hydroxy-β-methylbutyrate free acid supplementation plus eccentric resistance training (HMB+ERT) groups. Training groups undertook eccentric resistance training (6 weeks, 3 times a week) and supplement groups consumed β-hydroxy-β-methylbutyrate free acid (HMB-FA) orally (76 mg kg^-1 day^-1). Twenty-four hours after the last training session, serum and triceps brachii muscle samples were collected and sent to the laboratory for analysis. Two-way ANOVA and Pearson correlation were employed (significance level: P<0.05). The results showed that eccentric resistance training increases skeletal muscle PGC-1α gene expression, as well as serum levels of irisin and nesfatin-1 (P=0.001). Eccentric resistance training decreased the serum concentration of resistin (P=0.001). HMB-FA supplementation increased skeletal muscle PGC-1α gene expression (P=0.002), as well as the serum concentration of irisin and nesfatin-1 (P=0.001), but decreased the serum concentration of resistin (P=0.001). Significant correlations were observed between PGC-1α gene expression and serum concentrations of irisin, nesfatin-1 and resistin. HMB-FA supplementation with eccentric resistance training may induce crosstalk between peptide release from other tissues and increases maximal muscle strength. The combination of the two interventions had a more substantial effect than each in isolation.

Safety and efficacy of l-leucine produced by fermentation with Escherichia coli NITE BP-02351 for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l-leucine produced by fermentation with Escherichia coli NITE BP-02351 when used as nutritional additive or as feed flavouring compound in feed and water for drinking for all animal species. The product under assessment is l-leucine produced by fermentation with a genetically modified strain of E. coli (NITE BP-02351). The production strain and its recombinant DNA were not detected in the final products. l-Leucine, manufactured by fermentation with E. coli NITE BP-02351, does not give rise to any safety concern to the production strain. The use of l-leucine produced with E. coli NITE BP-02351 is safe for the target species when used to supplement the diet in appropriate amounts. It is safe at the proposed use level of 25 mg/kg when used as flavouring compound for all animal species. The use of l-leucine produced by fermentation with E. coli NITE BP-02351 in animal nutrition raises no safety concerns for consumers of animal products. The additive is not irritating to the skin or eyes and is not a skin sensitiser. There is a risk for persons handling the additive from the exposure to endotoxins by inhalation. The use of l-leucine produced by E. coli NITE BP-02351 as feed additive does not represent a risk to the environment. The additive l-leucine produced by E. coli NITE BP-02351 is regarded as an effective source of the amino acid l-leucine when used as nutritional additive. For the supplemental l-leucine to be as efficacious in ruminants as in non-ruminant species, it requires protection against degradation in the rumen. It is also considered efficacious as feed flavouring compound under the proposed conditions of use.

Current feeding strategies to improve pork intramuscular fat content and its nutritional quality

Pork, one of the most consumed meats worldwide, has been facing major challenges regarding its low sensory quality and unhealthy image of fat. This chapter addresses current feeding strategies to ameliorate pork sensory attributes and nutritional quality by increasing intramuscular fat deposition and improving fatty acid composition, respectively. Dietary protein reduction, alone or combined with some components, contributes to satisfy consumer requirements and enhances the competitiveness of the meat industry with higher pork quality and lower production costs. In addition, feeding sources of n-3 polyunsaturated fatty acids to pigs, mainly from marine origin (rich in eicosapentaenoic and docosahexaenoic acids), increases their content in pork, thus improving the health value of its fatty acid profile. In the near future, the inclusion of microalgae and seaweeds in feed represents a promising approach for the maintenance and development of the livestock sector, as an environmental friendly alternative to balance food and feed industries.

Extracellular Proteolytic Activity and Amino Acid Production by Lactic Acid Bacteria Isolated from Malaysian Foods

Amino acids (AAs) are vital elements for growth, reproduction, and maintenance of organisms. Current technology uses genetically engineered microorganisms for AAs production, which has urged the search for a safer food-grade AA producer strain. The extracellular proteolytic activities of lactic acid bacteria (LAB) can be a vital tool to hydrolyze extracellular protein molecules into free AAs, thereby exhibiting great potential for functional AA production. In this study, eight LAB isolated from Malaysian foods were determined for their extracellular proteolytic activities and their capability of producing AAs. All studied LAB exhibited versatile extracellular proteolytic activities from acidic to alkaline pH conditions. In comparison, Pediococcus pentosaceus UP-2 exhibited the highest ability to produce 15 AAs extracellularly, including aspartate, lysine, methionine, threonine, isoleucine, glutamate, proline, alanine, valine, leucine, tryptophan, tyrosine, serine, glycine, and cystine, followed by Pediococcus pentosaceus UL-2, Pediococcus acidilactici UB-6, and Pediococcus acidilactici UP-1 with 11 to 12 different AAs production detected extracellularly. Pediococcus pentosaceus UL-6 demonstrated the highest increment of proline production at 24 h of incubation. However, Pediococcus acidilactici UL-3 and Lactobacillus plantarum I-UL4 exhibited the greatest requirement for AA. The results of this study showed that different LAB possess different extracellular proteolytic activities and potentials as extracellular AA producers.

Leucine alone or in combination with glutamic acid, but not with arginine, increases biceps femoris muscle and alters muscle AA transport and concentrations in fattening pigs

Forty-eight Duroc × Large White × Landrace pigs with an average initial body weight of 77.09 ± 1.37 kg were used to investigate the effects of combination of leucine (Leu) with arginine (Arg) or glutamic acid (Glu) on muscle growth, free amino acid profiles, expression levels of amino acid transporters and growth-related genes in skeletal muscle. The animals were randomly assigned to one of the four treatment groups (12 pigs/group, castrated male:female = 1:1). The pigs in the control group were fed a basal diet (13% Crude Protein), and those in the experimental groups were fed the basal diet supplemented with 1.00% Leu (L group), 1.00% Leu + 1.00% Arg (LA group) or 1.00% Leu + 1.00% Glu (LG group). The experiment lasted for 60 days. Results showed an increase (p < 0.05) in biceps femoris (BF) muscle weight in the L group and LG group relative to the basal diet group. In longissimus dorsi (LD) muscle, Lys, taurine and total essential amino acid concentration increased in the LG group relative to the basal diet group (p < 0.05). In LG group, Glu and carnosine concentrations increased (p < 0.05) in the BF muscle, when compared to the basal diet group. The Leu and Lys concentrations of BF muscle were lower in the LA group than that in the L group (p < 0.05). A positive association was found between BF muscle weight and Leu concentration (p < 0.05). The LG group presented higher (p < 0.05) mRNA levels of ASCT2, LAT1, PAT2, SANT2 and TAT1 in LD muscle than those in the basal diet group. The mRNA levels of PAT2 and MyoD in BF muscle were upregulated (p < 0.05) in the LG group, compared with those in the basal diet group. In conclusion, Leu alone or in combination with Glu is benefit for biceps femoris muscle growth in fattening pig.