Alpha-Ketoglutarate in Low-Protein Diets for Growing Pigs: Effects on Cecal Microbial Communities and Parameters of Microbial Metabolism

Effects of selenium-enriched yeast dietary supplementation on egg quality, gut morphology and caecal microflora of laying hens

Selenium (Se) is an essential micronutrient for humans and animals and is a powerful antioxidant that can promote reproductive and immune functions. The purpose of this study was to evaluate the effects of supplemental dietary selenium-enriched yeast (SeY) on egg quality, gut morphology and microflora in laying hens. In total, 100 HY-Line Brown laying hens (45-week old) were randomly allocated to two groups with 10 replicates and fed either a basal diet (without Se supplementation) or a basal diet containing 0.2 mg/kg Se in the form of SeY for 8 weeks. The Se supplementation did not have a significant effect on egg quality and intestinal morphology of laying hens. Based on the 16S rRNA sequencing, SeY dietary supplementation effectively modulated the cecal microbiota structure. An alpha diversity analysis demonstrated that birds fed 100 mg/kg SeY had a higher cecal bacterial diversity. SeY dietary addition elevated Erysipelotrichia (class), Lachnospiraceae (family), Erysipelotrichaceae (family) and Ruminococcus_torques_group (genus; p < .05). Analysis of microbial community-level phenotypes revealed that SeY supplementation decreased the microorganism abundance of facultatively anaerobic and potentially pathogenic phenotypes. Overall, SeY supplementation cannot significantly improve intestinal morphology; however, it modulated the composition of cecal microbiota toward a healthier gut.

α-Ketoglutarate for Preventing and Managing Intestinal Epithelial Dysfunction

The epithelium lining the intestinal tract serves a multifaceted role. It plays a crucial role in nutrient absorption and immune regulation and also acts as a protective barrier, separating underlying tissues from the gut lumen content. Disruptions in the delicate balance of the gut epithelium trigger inflammatory responses, aggravate conditions such as inflammatory bowel disease, and potentially lead to more severe complications such as colorectal cancer. Maintaining intestinal epithelial homeostasis is vital for overall health, and there is growing interest in identifying nutraceuticals that can strengthen the intestinal epithelium. α-Ketoglutarate, a metabolite of the tricarboxylic acid cycle, displays a variety of bioactive effects, including functioning as an antioxidant, a necessary cofactor for epigenetic modification, and exerting anti-inflammatory effects. This article presents a comprehensive overview of studies investigating the potential of α-ketoglutarate supplementation in preventing dysfunction of the intestinal epithelium.

Enzymolytic soybean meal-impact on growth performance, nutrient digestibility, antioxidative capacity, and intestinal health of weaned piglets

Enzymolytic soybean meal (ESBM) enriches free amino acids and small peptides, while mitigating anti-nutritional factors. Substituting soybean meal with ESBM enhances animal performance, though optimal piglet dietary supplementation levels vary. The present study aimed to assess the impact of ESBM on the growth performance, nutrient digestibility, antioxidative capacity and intestinal health of weaned piglets. A total of 120 piglets (initial body weight, 7.0 ± 0.4 kg) were randomly allocated into 4 dietary groups, each comprising 5 replicates with 6 piglets per replicate. The control group received the basal diet, while the experimental groups were fed diets containing 2, 4% or 8% ESBM as a replacement for soybean meal over 28 days. Compared with the control group, piglets supplemented with 4% ESBM exhibited a significant increase (p < 0.05) in average daily gain and the apparent total tract digestibility of dry matter, ether extract and gross energy (p < 0.05), alongside a notable decrease (p < 0.05) in diarrhea incidence. Fed ESBM linearly increased (p < 0.05) the villus height in the ileum of piglets. The levels of superoxide dismutase and total antioxidant capacity in serum of piglets increased (p < 0.05) in the 2 and 4% ESBM groups, while diamine oxidase content decreased (p < 0.05) in the 4 and 8% ESBM group. ESBM inclusion also upregulated (p < 0.05) the expression of superoxide dismutase 1 (SOD-1), Catalase (CAT) and claudin-1 mRNA. In terms of cecal fermentation characteristics, ESBM supplementation resulted in a increase (p < 0.05) in valerate content and a linear rise (p < 0.05) in propionate, butyrate, and total short-chain fatty acids levels, accompanied by a decrease (p < 0.05) in the concentrations of tryptamine and NH3 in cecal digesta. ESBM had no discernible effect on cecal microbial composition. In summary, substitution of soybean meal with ESBM effectively improved the growth performance of piglets by enhancing nutrient digestibility, antioxidant capacity, intestinal barrier and cecal microbial fermentation characteristics, with the optimal replacement level identified at 4%.

Dietary supplementation of proteases on growth performance, nutrient digestibility, blood characteristics and gut microbiota of growing pigs fed sorghum-based diets

Low-tannin sorghum is an excellent energy source in pig diets. However, sorghum contains several anti-nutritional factors that may have negative effects on nutrient digestibility. The impacts of proteases on growth performance, nutrient digestibility, blood parameters, and gut microbiota of growing pigs fed sorghum-based diets were studied in this study. Ninety-six pigs (20.66 ± 0.65 kg BW) were allocated into three groups (eight pens/group, four pigs/pen): (1) CON (control diet, sorghum-based diet included 66.98% sorghum), (2) PRO1 (CON + 200 mg/kg proteases), (3) PRO2 (CON + 400 mg/kg proteases) for 28 d. No differences were observed in growth performance and apparent total tract digestibility (ATTD) of nutrients between CON and PRO1 groups. Pigs fed PRO2 diet had increased (P < 0.05) BW on d 21 and 28, and increased (P < 0.05) average daily gain during d 14-21 and the overall period compared with pigs fed CON diet. In addition, pigs fed PRO2 diet had improved (P < 0.05) ATTD of gross energy, CP, and DM compared with pigs fed CON and PRO1 diets. Pigs fed PRO2 diet had lower (P < 0.05) plasma globulin (GLB) level and higher (P < 0.05) plasma glucose, albumin (ALB) and immunoglobulin G levels, and ALB/GLB ratio than pigs fed CON and PRO1 diets. Furthermore, pigs fed PRO2 diet had decreased (P < 0.05) the relative abundance of Acidobacteriota at the phylum level and increased (P < 0.05) the relative abundance of Prevotella_9 at the genus level. The linear discriminant analysis effect size analysis also showed that pigs fed PRO2 diet had significantly enriched short-chain fatty acid-producing bacteria, such as Subdoligranulum and Parabacteroides. In conclusion, protease supplementation at 400 mg/kg improved the growth performance of growing pigs fed sorghum-based diets, which may be attributed to the improvement of nutrient digestibility, host metabolism, immune status and associated with the altered gut microbiota profiles.

The Role of Short-Chain Fatty Acids in Acute Pancreatitis

Acute pancreatitis (AP) is a digestive emergency and can develop into a systematic illness. The role of the gut in the progression and deterioration of AP has drawn much attention from researchers, and areas of interest include dysbiosis of the intestinal flora, weakened intestinal barrier function, and bacterial and endotoxin translocation. Short-chain fatty acids (SCFAs), as one of the metabolites of gut microbiota, have been proven to be depleted in AP patients. SCFAs help restore gut homeostasis by rebuilding gut flora, stabilizing the intestinal epithelial barrier, and regulating inflammation. SCFAs can also suppress systematic inflammatory responses, improve the injured pancreas, and prevent and protect other organ dysfunctions. Based on multiple beneficial effects, increasing SCFAs is an essential idea of gut protective treatment in AP. Specific strategies include the direct use of butyrate or indirect supplementation through fiber, pre/pro/synbiotics, or fecal microbiota transplantation as a promising adjective therapy to enteral nutrition.

The Role of Lactoferrin in Intestinal Health

The intestine represents one of the first barriers where microorganisms and environmental antigens come into tight contact with the host immune system. A healthy intestine is essential for the well-being of humans and animals. The period after birth is a very important phase of development, as the infant moves from a protected environment in the uterus to one with many of unknown antigens and pathogens. In that period, mother's milk plays an important role, as it contains an abundance of biologically active components. Among these components, the iron-binding glycoprotein, lactoferrin (LF), has demonstrated a variety of important benefits in infants and adults, including the promotion of intestinal health. This review article aims to provide a compilation of all the information related to LF and intestinal health, in infants and adults.

Lacticaseibacillus rhamnosus Probio-M9 enhanced the antitumor response to anti-PD-1 therapy by modulating intestinal metabolites

BACKGROUND

Probiotics have been increasingly proposed for enhancing immune checkpoint blockade (ICB) treatments against cancer. However, its causal relationship with immunotherapeutic efficacy remains unclear, which promoted us to explore if and how probiotic Lacticaseibacillus rhamnosus Probio-M9 manipulates gut microbiome for expected outcomes.

METHODS

We evaluated the effects of Probio-M9 on the anti-PD-1 treatment against colorectal cancer in mice via a multi-omics approach. We defined the mechanisms of Probio-M9-mediated antitumor immunity by comprehensive analyses of metagenome and metabolites of commensal gut microbes as well as the immunologic factors and serum metabolome of the host.

FINDINGS

The results indicated that Probio-M9 intervention strengthened the anti-PD-1-based tumor inhibition. Both prophylactic and therapeutic administration of Probio-M9 showed conspicuous performance in controlling tumor growth with ICB treatment. The supplement of Probio-M9 modulated enhanced immunotherapy response through promoting beneficial microbes (e.g., Lactobacillus and Bifidobacterium animalis), producing beneficial metabolites including butyric acids in the gut, and accumulating blood-derived α-ketoglutaric acid, N-acetyl-l-glutamic acid and pyridoxine in particular, which promoted the infiltration and activation of cytotoxic T lymphocytes (CTLs) and suppressing the function of regulatory T cells (Tregs) in the tumor microenvironment (TME). Subsequently, we found that enhanced immunotherapeutic response was transmissible by transplanting either post-probiotic-treatment gut microbes or intestinal metabolites to new tumor-bearing mice.

INTERPRETATION

This study offered valuable insight into the causal role of Probio-M9 in correcting the defects in gut microbiota that compromised anti-PD-1 therapeutic efficacy, which can be used as an alternative synergetic agent with ICB for clinical cancer treatment.

FUNDING

This research was supported by Research Fund for the National Key R&D Program of China (2022YFD2100702), Inner Mongolia Science and Technology Major Projects (2021ZD0014), and China Agriculture Research System of MOF and MARA.

Mulberry leaf extract improves intestinal barrier function and displays beneficial effects on colonic microbiota and microbial metabolism in weaned piglets

BACKGROUND

Mulberry leaf extract (MLE) extracted from mulberry leaves is rich in a variety of bioactive ingredients and can be used as feed additives of weaned piglets. The present study was conducted to evaluate the effects of dietary MLE supplementation on intestinal barrier function, colon microbial numbers and microbial metabolites of weaned piglets.

RESULTS

MLE supplementation increased the villus height and the villus height/crypt depth ratio in jejunum and ileum (P < 0.05), increased the mRNA expression of ZO-1, Claudin-1 and MUC-2 in the ileal mucosa (P < 0.05), and decreased the serum level of lipopolysaccharide (P < 0.01). Meanwhile, MLE reduced the mRNA expression of tumor necrosis factor-α and interleukin-1β (P < 0.05) and increased secretory immunoglobulin A level in the ileal mucosa (P < 0.05). In addition, MLE increased the numbers of beneficial bacteria Bifidobacterium and Lactobacillus (P < 0.05) and decreased the number of potential pathogenic bacteria Escherichia coli (P < 0.05) in the colon. Correspondingly, MLE supplementation reduced the pH value of colonic digesta (P < 0.05) and altered the microbial fermentation pattern of the colon by increasing the concentrations of microbial metabolites derived from carbohydrates fermentation such as lactate, acetate, butyrate and total short-chain fatty acids (P < 0.05), and decreasing the concentrations of microbial metabolites derived from amino acid fermentation such as p-cresol, skatole, spermine, histamine and tryptamine (P < 0.05).

CONCLUSION

MLE supplementation improved intestinal barrier function and displayed beneficial effects on colon microbes and microbial metabolism in weaned piglets. © 2022 Society of Chemical Industry.

Effects of low protein diet with a balanced amino acid pattern on growth performance, meat quality and cecal microflora of finishing pigs

BACKGROUND

The present study aimed to investigate the effects of low protein diets balanced with four amino acids on growth performance, meat quality and cecal microflora of finishing pigs. Fifty-four healthy hybrid barrows (Duroc × Landrace × Yorkshire) with an average body weight of 70.12 ± 4.03 kg were randomly assigned to one of the three dietary treatments with six replicate pens per treatment (three barrows per pen). The three dietary treatments included a normal protein diet (NP), a low protein diet (LP) and a very low protein diet (VLP).

RESULTS

The average daily gain, average daily feed intake and feed conversion ratio of pigs were not significantly changed with the LP and VLP diets compared to the NP diet (P > 0.05). The water holding capacity and shear force of longissimus dorsi muscle were decreased, whereas the intramuscular fat content of the longissimus dorsi muscle was increased (P < 0.05) in pigs fed with the LP and VLP diets compared to the NP diet. The contents of saturated fatty acids in muscle were decreased (P < 0.05), whereas the content of polyunsaturated fatty acids in muscle was increased (P < 0.01) with the VLP diet compared to the NP diet. The contents of histamine, spermidine, spermine and tyramine of muscle were decreased with the VLP diet compared to the NP diet (P < 0.05). The relative abundance of Turicibacter, Terrisporobacter, Clostridium_sensu_stricto_1 and UCG-005 was higher (P < 0.05), whereas the relative abundance of Lactobacillus and Streptococcus was lower (P < 0.05) in pigs fed with the LP and VLP diets compared to the NP diet. Based on the correlation of cecal microbiota and cecal biogenic amine, the contents of tyramine, spermidine and histamine were negatively correlated with the abundance of Terrisporobacter (P < 0.01) and the content of histamine was positively correlated with the abundance of Lactobacillus (P < 0.01).

CONCLUSION

Balanced with four essential amino acids, the VLP diet with crude protein levels decreased by > 4% increased the intramuscular fat content, changed the fatty acid and amino acid composition of longissimus dorsi muscle and the profile of cecum microbiota, and reduced the content of cecum bioamine, with no negative effect on the growth performance of pigs. © 2022 Society of Chemical Industry.

Effects of Long-Term Low-Protein Diets Supplemented with Sodium Dichloroacetate and Glucose on Metabolic Biomarkers and Intestinal Microbiota of Finishing Pigs

The objective of this study was to evaluate the effects of low-protein (LP) diets supplemented with sodium dichloroacetate (DCA) and glucose (GLUC) on metabolic markers and intestinal microbiota of finishing pigs. A total of 80 crossbred growing barrows were allocated randomly to one of the five treatments, including the normal protein level diet (CON), the LP diets, LP with 120 mg/kg DCA (LP + DCA) or 1.8% glucose (LP + GLUC), and LP with 120 mg/kg DCA and 1.8% glucose (LP + DCA + GLUC). The LP diet increased the plasma HDL, triglyceride, and cholesterol concentrations and reduced the bile acid, urea nitrogen, albumin, and total protein concentrations compared to the CON diet (p < 0.05). The LP + DCA + GLUC diet reduced the plasma VLDL, triglyceride, and cholesterol concentrations and increased the bile acid concentration compared with the LP diet (p < 0.05). Pigs fed the LP + DCA and LP + GLUC diets showed reduced 3-Hydroxy-3-Methylglutaryl-CoA Reductase content and increased Cytochrome P450 Family 7 Subfamily A Member 1 activity of liver compared that of the CON diet (p < 0.05). Moreover, the LP diets with or without DCA and GLUC supplementation increased the relative abundance of colonic microbiota related to carbohydrate fermentation in finishing pigs. In conclusion, 120 mg/kg DCA or 1.8% GLUC supplementation in an LP diet modulated the hepatic lipid metabolism of pigs, while the DCA along with GLUC supplementation likely improved the lipid metabolism by stimulating bile acid secretion.

Combining fecal microbiome and metabolomics to reveal the disturbance of gut microbiota in liver injury and the therapeutic mechanism of shaoyao gancao decoction

Chemical liver injury is closely related to gut microbiota and its metabolites. In this study, we combined 16S rRNA gene sequencing, ¹H NMR-based fecal metabolomics and GC-MS to evaluate the changes in gut microbiota, fecal metabolites and Short-chain fatty acids (SCFAs) in CCl₄-induced liver injury in Sprague-Dawley rats, and the therapeutic effect of Shaoyao Gancao Decoction (SGD). The results showed that CCl₄-induced liver injury overexpressed CYP2E1, enhanced oxidative stress, decreased antioxidant enzymes (SOD, GSH), increased peroxidative products MDA and inflammatory responses (IL-6, TNF-α), which were ameliorated by SGD treatment. H&E staining showed that SGD could alleviate liver tissue lesions, which was confirmed by the recovered liver index, ALT and AST. Correlation network analysis indicated that liver injury led to a decrease in microbiota correlation, while SGD helped restore it. In addition, fecal metabolomic confirmed the PICRUSt results that liver injury caused disturbances in amino acid metabolism, which were modulated by SGD. Spearman’s analysis showed that liver injury disrupted ammonia transport, urea cycle, intestinal barrier and energy metabolism. Moreover, the levels of SCFAs were also decreased, and the abundance of Lachnoclostridium, Blautia, Lachnospiraceae_NK4A136_group, UCG-005 and Turicibacter associated with SCFAs were altered. However, all this can be alleviated by SGD. More importantly, pseudo germ-free rats demonstrated that the absence of gut microbiota aggravated liver injury and affected the efficacy of SGD. Taken together, we speculate that the gut microbiota has a protective role in the pathogenesis of liver injury, and has a positive significance for the efficacy of SGD. Moreover, SGD can treat liver injury by modulating gut microbiota and its metabolites and SCFAs. This provides useful evidence for the study of the pathogenesis of liver injury and the clinical application of SGD.

Low Protein Diets Supplemented With Alpha-Ketoglutarate Enhance the Growth Performance, Immune Response, and Intestinal Health in Common Carp (Cyprinus carpio)

To investigate the effects of alpha-ketoglutarate (AKG) supplementation in a low protein (LP) diet on the growth performance, immune response, and intestinal health of common carp (Cyprinus carpio), 600 carp were randomly divided into five dietary groups: a normal protein (NP) diet containing 32% crude protein, an LP diet formulated with 28% crude protein, and LP with AKG at 0.4%, 0.8%, and 1.2% (dry matter). After an 8-week trial period, the results demonstrated that an LP diet led to a decrease in performance, immune response, and intestinal barrier function. Compared with the LP group, the final body weight and weight gain rate in the LP+0.4% AKG group were significantly higher, the feed conversion ratio was significantly decreased with the addition of 0.4% and 0.8% AKG. The supplementation with 0.4% and 0.8% AKG markedly increased the activities of T-SOD and GSH-Px, as well as the expression levels of GPX1a and GPX1b relative to the LP group, whereas the MDA content was significantly decreased in the LP+0.4% AKG group. In addition, the expression levels of tight junctions including claudin-3, claudin-7, ZO-1, and MLCK were significantly up-regulated in the LP+0.4% AKG group, and the relative expression levels of the pro-inflammatory factors IL-1β and IL-6α were significantly lower with the addition of 0.4%, 0.8%, and 1.2% AKG. Moreover, the abundance of Proteobacteria in the LP+0.4% AKG group was lower than that in the LP group, and the abundance of Firmicutes and Fusobacteria was higher at the phylum level. The abundance of Citrobacter in the LP+0.4% AKG group was decreased compared to the LP group, while the abundance of Aeromonas was increased at the genus level. In short, the effects of AKG on the intestinal health of the common carp were systematically and comprehensively evaluated from the perspectives of intestinal physical barrier, chemical barrier, biological barrier, and immune barrier. We found that an LP diet supplemented with 0.4% AKG was beneficial to the growth performance and intestinal health of common carp.

Rumen Microbiome and Metabolome of High and Low Residual Feed Intake Angus Heifers

Feed cost is the greatest expense during cattle production; therefore, reducing it is critical to increasing producer profits. In ruminants, the microbial population is important to nutrient digestion and absorption in the rumen. The objective of this study was to investigate the relationships among rumen bacteria, rumen metabolites, and the residual feed intake (RFI) phenotype of beef cattle. Twelve Angus heifers were selected to be sampled and divided into high RFI (HRFI; n = 6) group and low RFI (LRFI; n = 6) group according to their RFI classification determined during the feedlot-finishing period. After the ruminal liquid samples were collected at slaughter, Illumina MiSeq sequencing of the 16S rRNA V3-V4 region and liquid chromatography-mass spectrometry (LC-MS) were performed to determine their bacterial composition and metabolites, respectively. At the phylum level, the relative abundance of Proteobacteria was higher in the LRFI group than in the HRFI group (P < 0.01). At the family level, the relative abundances of Rikenellaceae (P < 0.01), Ruminococcaceae, Bacteroidales_S24-7_group, and Lachnospiraceae (P < 0.05) were significantly higher in the LRFI group. At the genus level, the relative abundances of Rikenellaceae_RC9_gut_group and Ruminiclostridium_1 were higher in the LRFI group (P < 0.01), as were the relative abundances of norank_f__Bacteroidales_S24-7_group, Lachnospiraceae_ND3007_group, and Lachnospiraceae_NK3A20_group (P < 0.05). Moreover, the genera Rikenellaceae_RC9_gut_group, Ruminococcaceae_NK4A214_group, Christensenellaceae_R-7_group, Ruminococcaceae_UCG-010, Lachnospiraceae_ND3007_group, Ruminiclostridium_1, and Lachnospiraceae_NK3A20_group were negatively associated with the RFI; both foundational and key species are associated with feed efficiency phenotype. In addition, rumen metabolomics analysis revealed that the RFI was associated with significantly altered concentrations of rumen metabolites involved in protein digestion and absorption, Linoleic acid metabolism, Lysine degradation, and Fatty acid degradation. Correlation analysis revealed the potential relationships between the significantly differential ruminal metabolites and the genera ruminal bacteria. The present study provides a better understanding of rumen bacteria and metabolites of beef cattle with different RFI phenotypes and the relationships among them, which are potentially important for the improvement of beef cattle feed efficiency.

Different dietary protein sources influence growth performance, antioxidant capacity, immunity, fecal microbiota and metabolites in weaned piglets

The inclusion of high-quality proteins are commonly used in swine production. Our research investigated the effects of hydrolyzed wheat protein (HWP), fermented soybean meal (FSBM), and enzyme-treated soybean meal (ESBM) on growth performance, antioxidant capacity, immunity, fecal microbiota and metabolites of weaned piglets. A total of 144 piglets (weaned at 28 d) were allotted to 3 dietary treatments with 6 replicate pens per treatment and 8 piglets per pen. This study included 2 periods: d 0 to14 for phase 1 and d 15 to 28 for phase 2. Dietary treatments contained 15.90% HWP, 15.80% FSBM, and 15.10% ESBM in phase 1, and 7.90% HWP, 7.80% FSBM, and 7.50% ESBM in phase 2, respectively. The ADG of piglets in ESBM was increased (P < 0.05) compared with HWP and FSBM during d 1-28. Compared with HWP and FSBM, ESBM increased (P < 0.05) the ferric reducing ability of plasma (FRAP), and the serum level of superoxide dismutase (SOD) in piglets on d 14, as well as increased (P < 0.05) the serum FRAP level in piglets on d 28. ESBM decreased (P < 0.05) serum levels of DAO and IL-1β in piglets compared with HWP on d 28. ESBM enhanced (P < 0.05) the relative abundance of Bacteroidetes, Oscillospiraceae and Christensenellaceae, as well as reduced the relative abundance of Clostridiaceae in the feces compared with HWP and FSBM. The PICRUSt analysis revealed that the number of gene tags related to degradation of valine, leucine and isoleucine, as well as lysine degradation in ESBM were lower (P < 0.05) than that in HWP and FSBM. ESBM increased (P < 0.05) the fecal butyrate level in piglets compared with FSBM, and ESBM tended to decrease (P = 0.076) the fecal cadaverine level. Overall, ESBM had advantages over HWP and FSBM in improving antioxidant status, immune function, fecal bacteria and metabolites for weaned piglets.

Emissions of Gaseous Pollutants from Pig Farms and Methods for their Reduction – A Review

Agriculture contributes significantly to anthropogenic emissions of greenhouse gases (GHG). Livestock production, including pig production, is associated with several gaseous pollutants released into the atmosphere, including carbon dioxide (CO2), methane (CH4), ammonia (NH3) and nitrous oxide (N2O). Emissions of volatile organic compounds (VOCs), including alcohols, aldehydes, and aromatic and aliphatic hydrocarbons, as well as typically odorous pollutants, are an inseparable element of raising and breeding farm animals. These emissions can degrade local and regional air quality, contribute to surface water eutrophication and acid rain, and increase the greenhouse gas footprint of the production sector. The paper is organized as follows. First, the sources and factors influencing the level of emissions from pig houses are described. Next, the effects of dietary methods (optimization of animal diets), hygienic methods (including microclimate optimization) and technological methods (application of technological solutions) for mitigating emissions from pigs are discussed.

Suitable ratio of dietary L-carnitine and α-ketoglutarate improves growth and health performance in Nile tilapia, Oreochromis niloticus

L-carnitine (LC) and α-Ketoglutarate (AKG) are important growth promoters used in aquafeed. The study aimed to evaluate the incorporation of LC and AKG at different ratios in the diet of tilapia (initial weight 1.38 ± 0.03 g) in order to facilitate lipid utilization and protein synthesis. Fish were fed six isonitrogenous (~ 30 g/100 g CP) and isolipidic (~ 6 g/100 g CL) diets containing graded LC/AKG ratios of 0 (Control), 0.11, 0.42, 1.00, 2.33 and 9.00 in six treatments for 60 days. Fish fed with LC/AKG ratios 2.33 and 9.00 showed significantly (P < 0.05) higher percentage weight gain, specific growth rate and protein efficiency ratio. Feed conversion ratio in fish-fed diets with LC/AKG ratio 9.00 improved significantly (p < 0.05) than other treatments. The whole-body protein content of tilapia and digestive enzyme activity were significantly higher with higher weight gain. The body lipid content was significantly lower in the LC/AKG ratio 9.00. The liver antioxidant parameters and activity of the immune components were significantly higher in the LC/AKG ratio 9 group. The lower serum triglyceride and cholesterol level was also recorded in LC/AKG ratio 9 group. The histology of the intestine and liver showed increased villi area and decreased lipid droplets, respectively, in tilapia fed with higher LC/AKG ratios. It was concluded from the above results that the higher LC and lower AKG (LC/AKG ratio 9.00) combination attributed maximum lipid utilization and higher protein efficiency and thus better growth performance in tilapia. This was also reflected in activity of digestive enzymes, antioxidant enzymes and immune status in tilapia.

Comparative effects of enzymatic soybean, fish meal and milk powder in diets on growth performance, immunological parameters, SCFAs production and gut microbiome of weaned piglets

Background

The objective of this study was to evaluate the replacement effects of milk powder (MK) and fish meal (FM) by enzymatic soybean (ESB) in diets on growth performance, immunological parameters, SCFAs production and gut microbiome of weaned piglets.

Methods

A total of 128 piglets with initial body weight at 6.95 ± 0.46 kg, were randomly assigned into 4 dietary treatments with 8 replicates per treatment and 4 piglets per replicate for a period of 14 d. Piglets were offered iso-nitrogenous and iso-energetic diets as follows: CON diet with MK and FM as high quality protein sources, ESB plus FM diet with ESB replacing MK, ESB plus MK diet with ESB replacing FM, and ESB diet with ESB replacing both MK and FM.

Results

No significant differences were observed in growth performance among all treatments (P > 0.05). However, piglets fed ESB plus FM or ESB diet had increased diarrhea index (P<0.01), and lower digestibility of dry matter (DM), gross energy (GE) or crude protein (CP), relative to piglets fed CON diet (P <  0.01). Moreover, the inclusion of ESB in diet markedly decreased the plasma concentration of HPT and fecal concentration of butyric acid (BA) (P<0.01). The High-throughput sequencing of 16S rRNA gene V3−V4 region of gut microbiome revealed that the inclusion of ESB in diet increased the alpha diversity, and the linear discriminant analysis effect size (LEfSe) showed that piglets fed with ESB plus FM or ESB diet contained more gut pathogenic bacteria, such as g_Peptococcus, g_Veillonella and g_Helicobacter.

Conclusion

The inclusion of ESB in diet did not markedly affect growth performance of piglets, but the replacement of MK or both MK and FM by ESB increased diarrhea index, which could be associated with lower nutrients digestibility and more gut pathogenic bacteria. However, piglets fed diet using ESB to replace FM did not markedly affect gut health-related parameters, indicating the potential for replacing FM with ESB in weaning diet.

Low Crude Protein Diet Affects the Intestinal Microbiome and Metabolome Differently in Barrows and Gilts

Low protein diets are commonly used in the growing-finishing pig stage of swine production; however, the effects of low dietary protein on the intestinal microbiota and their metabolites, and their association with pig sex, remain unclear. The present study aimed to assess the impact of a low crude protein (CP) diet on the gut microbiome and metabolome, and to reveal any relationship with sex. Barrows and gilts (both n = 24; initial body = 68.33 ± 0.881 kg) were allocated into two treatments according to sex. The four groups comprised two pairs of gilts and barrows fed with a high protein diet (CP 17% at stage I; CP 13% at stage II) and a low protein diet (CP 15% at stage I; CP 11% at stage II), respectively, for 51 d. Eight pigs in each group were slaughtered and their colon contents were collected. Intestinal microbiota and their metabolites were assessed using 16S rRNA sequencing and tandem mass spectrometry, respectively. The low protein diet increased intestinal microbiota species and richness indices (P < 0.05) in both sexes compared with the high protein diet. The sample Shannon index was different (P < 0.01) between barrows and gilts. At the genus level, unidentified Clostridiales (P < 0.05), Neisseria (P < 0.05), unidentified Prevotellaceae (P < 0.01) and Gracilibacteria (P < 0.05) were affected by dietary protein levels. The relative abundance of unidentified Prevotellaceae was different (P < 0.01) between barrows and gilts. The influence of dietary protein levels on Neisseria (P < 0.05), unidentified Prevotellaceae (P < 0.01) and Gracilibacteria (P < 0.05) were associated with sex. Metabolomic profiling indicated that dietary protein levels mainly affected intestinal metabolites in gilts rather than barrows. A total of 434 differentially abundant metabolites were identified in gilts fed the two protein diets. Correlation analysis identified that six differentially abundant microbiota communities were closely associated with twelve metabolites that were enriched for amino acids, inflammation, immune, and disease-related metabolic pathways. These results suggested that decreasing dietary protein contents changed the intestinal microbiota in growing-finishing pigs, which selectively affected the intestinal metabolite profiles in gilts.

Effects of Combined Supplementation of Macleaya cordata Extract and Benzoic Acid on the Growth Performance, Immune Responses, Antioxidant Capacity, Intestinal Morphology, and Microbial Composition in Weaned Piglets

Because the use of antibiotics is forbidden, piglets experience a considerable weanling stress, resulting in increased incidence of diarrhea and death. Macleaya cordata extract or benzoic acid have anti-inflammatory, antioxidant, and antimicrobial activities that makes them potential antibiotic alternatives. The objective of this study was to evaluate the potential effects of feed supplemented with Macleaya cordata extract and benzoic acid on growth performance, immunity, antioxidant capacity, intestinal morphology, and microflora in weaned piglets. Twenty-four weaned piglets [Duroc × (Large White × Landrace)] 28 days of age and weighing 8.41 ± 0.13 kg were randomly divided in equal numbers (n = 8) into three groups fed a basal diet (CON), CON + 20 mg/kg flavomycin + 50 mg/kg quinocetone (AGP), or CON + 50 mg/kg Macleaya cordata extract + 1,000 mg/kg benzoic acid (MB). Compared with the CON diet, dietary MB or AGP increased the final weight and average daily gain, and reduced feed efficiency and the diarrhea rate (P < 0.05). Compared with the CON diet, MB supplementation increased serum superoxide dismutase (SOD activity) and decreased malondialdehyde (MDA) content (P < 0.05). Serum interleukin (IL)-10 IgA and IgM were higher (P < 0.05) in MB-fed piglets than in CON-fed piglets. Piglets fed the MB diet had greater villus height and villus height to crypt depth ratio (VC) in the duodenum, villus height in the ileum, and lower crypt depth in the jejunum than did piglets given the CON diet (P < 0.5). Piglets in the MB group had increased concentrations of acetate, propionate, butyrate, and total short-chain fatty acids in the ileum or cecum compared with the CON and AGP groups (P < 0.05). Streptococcus proportion was lower in the MB than in the AGP group. Dietary MB increased the Lactobacillus and decreased Escherichia-Shigella populations compared with the CON group (P < 0.05). The study results indicate that MB can be used to replace AGP as a feed supplement for weaned piglets.

Effects of a microencapsulated formula of organic acids and essential oils on nutrient absorption, immunity, gut barrier function, and abundance of enterotoxigenic Escherichia coli F4 in weaned piglets challenged with E. coli F4

The objective was to study the effects of microencapsulated organic acids (OA) and essential oils (EO) on growth performance, immune system, gut barrier function, nutrient digestion and absorption, and abundance of enterotoxigenic Escherichia coli F4 (ETEC F4) in the weaned piglets challenged with ETEC F4. Twenty-four ETEC F4 susceptible weaned piglets were randomly distributed to 4 treatments including (1) sham-challenged control (SSC; piglets fed a control diet and challenged with phosphate-buffered saline (PBS)); (2) challenged control (CC; piglets fed a control diet and challenged with ETEC F4); (3) antibiotic growth promoters (AGP; CC + 55 mg·kg-1 of Aureomycin); and (4) microencapsulated OA and EO [P(OA+EO); (CC + 2 g·kg-1 of microencapsulated OA and EO]. The ETEC F4 infection significantly induced diarrhea at 8, 28, 34, and 40 hr postinoculation (hpi) (P < 0.05) in the CC piglets. At 28 d postinoculation (dpi), piglets fed P(OA+EO) had a lower (P < 0.05) diarrhea score compared with those fed CC, but the P(OA+EO) piglets had a lower (P < 0.05) diarrhea score compared with those fed the AGP diets at 40 dpi. The ETEC F4 infection tended to increase in vivo gut permeability measured by the oral gavaging fluorescein isothiocyanate-dextran 70 kDa (FITC-D70) assay in the CC piglets compared with the SCC piglets (P = 0.09). The AGP piglets had higher FITC-D70 flux than P(OA+EO) piglets (P < 0.05). The ETEC F4 infection decreased mid-jejunal VH in the CC piglets compared with the SCC piglets (P < 0.05). The P(OA+EO) piglets had higher (P < 0.05) VH in the mid-jejunum than the CC piglets. The relative mRNA abundance of Na+-glucose cotransporter and B0AT1 was reduced (P < 0.05) by ETEC F4 inoculation when compared with the SCC piglets. The AGP piglets had a greater relative mRNA abundance of B0AT1 than the CC piglets (P < 0.05). The ETEC F4 inoculation increased the protein abundance of OCLN (P < 0.05), and the AGP piglets had the lowest relative protein abundance of OCLN among the challenged groups (P < 0.05). The supplementation of microencapsulated OA and EO enhanced intestinal morphology and showed anti-diarrhea effects in weaned piglets challenged with ETEC F4. Even if more future studies can be required for further validation, this study brings evidence that microencapsulated OA and EO combination can be useful within the tools to be implemented in strategies for alternatives to antibiotics in swine production.

Effect of Durio zibethinus rind polysaccharide on functional constipation and intestinal microbiota in rats

The prevalence of constipation increases rapidly with the increased pressure of some people's life, which seriously affects the quality of life in related patients. In this study, the improvement of functional constipation by Durio zibethinus Murr rind polysaccharide (DZMP) and the effects of DZMP on intestinal microbiota were investigated in a constipation model of Sprague-Dawley (SD) rats established by loperamide hydrochloride. Results showed that DZMP at 200 mg/kg could significantly (P < 0.05) increase the intestinal transit rate, motilin, gastrin, substance P levels and concentration of short-chain fatty acids (SCFAs), reduce the somatostatin levels and improve the gastrointestinal peristalsis of rats. Sequencing showed that the Lachnospiraceae-NK4A136-group in the rats given 200 mg/kg DZMP (16.07%) was significantly higher than that of the model group (10.13%), while the Desulfovibrio was lower (2.99%) than that of the model group (4.19%). Principal co-ordinates analysis (PcoA) revealed a significant difference in intestinal microbiota composition between the model group and the high-dose DZMP group (200 mg/kg). The results demonstrated that DZMP has a regulatory effect of treating functional constipation and regulating intestinal flora in rats.

Effects of fucoidan on gut flora and tumor prevention in 1,2-dimethylhydrazine-induced colorectal carcinogenesis

Colorectal cancer (CRC) is one of the major malignancies in humans. This study was designed to evaluate the effects of fucoidan on gut flora and tumor prevention in 1,2-dimethylhydrazine-induced colorectal carcinogenesis in rats. We found that dietary fucoidan treatment decreased the tumor incidence and mean tumor weight and increased cell apoptosis. Fucoidan treatment decreased the expression of β-catenin C-Myc, CyclinD1 and Survivin, while the Hippo pathway was activated with increased phosphorylation levels of mammalian sterile 20-like kinase 1 and 2, large tumor suppressor 1 and 2, and Yes-associated protein. Compared with the model group, the levels of interleukin (IL)-17 and IL-23 were decreased, but the levels of interferon-γ, IL-4 and IL-10 were increased, in the fucoidan group. Fucoidan treatment increased natural killer cells in peripheral blood and the proportion of CD4+ T cells. Immunofluorescence detection of colorectal tumor tissues showed decreased expression of Foxp3 and up-regulated expression of CD68 in the fucoidan group. Moreover, fucoidan treatment decreased the levels of diamine oxidase and lipopolysaccharides and up-regulated the levels of tight junction proteins. 16S rDNA high-throughput sequencing revealed that fucoidan treatment decreased the abundance of Prevotella and increased the abundance of Alloprevotella. Fucoidan increased the levels of butyric acid and valeric acid compared to the model group. This study provides experimental evidence that dietary fucoidan may prevent colorectal tumorigenesis by regulating gut microecology and body immunity. Meanwhile, fucoidan activated the Hippo pathway and down-regulated the β-catenin pathway to induce tumor cell apoptosis and suppress tumor growth.

From Acidifiers to Intestinal Health Enhancers: How Organic Acids Can Improve Growth Efficiency of Pigs

Organic acids have been used successfully in pig production as a cost-effective performance-enhancing option and they continue to be the number one alternative to antibiotic growth promoters. The aim of this review is to provide the biological rationale behind organic acids use in pig production, focusing on their different effects along the gastrointestinal tract of pigs. Organic acids are reviewed for their antimicrobial properties and for their classic use as acidifiers, with particular attention to pH modulation and microflora control. Additional beneficial effects on intestinal health and general metabolism are presented and we explain the advantage of microencapsulation as a tool to deliver organic acids along the intestine.

Dietary Supplementation of ε-Polylysine Beneficially Affects Ileal Microbiota Structure and Function in Ningxiang Pigs

Intestinal microbiota plays an important role in the health of animals. However, little is known about the gut microbiota in Ningxiang pigs. Thus, we investigated how dietary supplementation with different ε-polylysine concentrations (0, 20, 40, 80, and 160 ppm) affected the ileal microbiota in Ningxiang pigs using a replicated 5 × 5 Latin square method. Each experimental period included 10 days for diet adaptation, 3 days for feces collection and 2 days for digesta collection. The ileal contents were collected and used for sequencing of the V3-V4 hypervariable region of the 16S rRNA gene. The results revealed that ε-polylysine significantly decreased the digestibility of crude protein and crude fiber, as well as the utilization of metabolizable energy (P < 0.05). The relative abundances of 19 bacterial genera significantly increased, while those of 26 genera significantly decreased (P < 0.05). In addition, ε-polylysine increased the abundance of some bacteria (e.g., Faecalibacterium, Bifidobacterium, and lactic acid bacteria) and inhibited some other bacteria (e.g., Micrococcaceae, Acinetobacter, Anaerococcus, Peptoniphilus, Dehalobacterium, Finegoldia, Treponema, and Brevundimonas). Furthermore, based on the 16S rRNA gene data and data from the precalculated GreenGenes database, bacterial communities in the ileal contents exhibited enhanced functional maturation, including changes in the metabolism of carbohydrates, amino acids (e.g., alanine, lysine, tryptophan, cysteine, and methionine), cofactors, and vitamins (e.g., biotin, thiamine, and folate), as well as in the activity of the insulin signaling pathway. This study suggests that ε-polylysine may influence the utilization of feed nutrients by Ningxiang pigs, including proteins, lipids, metabolizable energy, and fiber, by regulating the gut microbiota.

Effects of Dietary Supplementation of Alpha-Ketoglutarate in a Low-Protein Diet on Fatty Acid Composition and Lipid Metabolism Related Gene Expression in Muscles of Growing Pigs

Simple Summary

Alpha-ketoglutarate (AKG) is a critical intermediate in the tricarboxylic acid cycle. AKG has been reported to participate in energy production, promote protein synthesis, and improve amino acid metabolism. However, whether AKG functionally participates in the regulation of fat metabolism remains unknown. The objective of this experiment was to evaluate the impact of dietary supplementation with AKG on lipid metabolism in a pig model. The present results suggest that AKG supplementation in a reduced-protein diet could increase the intramuscular fat (IMF) and monounsaturated fatty acid (MUFA) contents in the biceps femoris muscles of pigs. These effects could be linked to the altered lipid metabolism related gene mRNA expression, which promotes the absorption and deposition of fatty acids in the muscle tissues. The results of this study can provide better understanding of the mechanisms by which dietary AKG modulates muscle lipid metabolism in pigs, and this could help to improve pig feeding strategies and supply high-quality pork for humans.

Abstract

The aim of the current study was to investigate whether dietary supplementation with alpha-ketoglutarate (AKG) in a reduced crude protein (CP) diet would affect fatty acid composition and lipid metabolism related gene expression in the muscles of growing pigs. A total of 27 Large White × Landrace growing pigs at 44 ± 1 d of age (11.96 ± 0.18 kg) were randomly allocated to three treatments (n = 9). Dietary treatments included: (1) normal protein diet with 20% crude protein (CP) (NP); (2) a low crude protein diet formulated to contain approximately 17% CP (LP); and (3) a low crude protein diet with 17% CP supplemented with 1% AKG at the expense of regular corn components (ALP). The experimental trial lasted 35 d. The results showed that compared with the NP and LP diets, supplementation with AKG in a low-protein diet increased the intramuscular fat (IMF), oleic acid (C18:1n-9), and monounsaturated fatty acid (MUFA) contents (p < 0.05), and tended to increase the percentage of palmitoleic acid (C16:1) and stearic acid (C18:0) (p < 0.10) in the biceps femoris and longissimus dorsi muscles of growing pigs. These effects may be associated with increased relative mRNA expression levels of fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), adipocyte determination and differentiation factor 1 (ADD1), fatty acid binding protein 4 (FABP4), and stearoyl-CoA desaturase (SCD) in skeletal muscle, indicating that AKG might be involved in the differential regulation of some key lipogenic genes in skeletal muscles of pigs.

Colonic Microbiota and Metabolites Response to Different Dietary Protein Sources in a Piglet Model

Dietary protein sources have the potential to affect the colon microbiome of piglets that will subsequently have a large impact on metabolic capabilities and hindgut health. This study explored the effects of different protein sources on the growth performance, diarrhea rate, apparent ileal digestibility (AID) of crude protein (CP), colonic mucin chemotypes, colonic microbiome, and microbial metabolites of piglets. Twenty-four piglets were randomly divided into four groups that received isoenergetic and isonitrogenous diets containing either Palbio 50 RD (P50), Soyppt-50% (S50), concentrated degossypolized cottonseed protein (CDCP), or fish meal (FM) as the sole protein source. The experimental diets did not affect the estimated daily gain (EDG), but P50 increased fecal score compared with S50 and CDCP. CDCP increased, but P50 reduced AID of CP in comparison to FM and S50. S50 and CDCP increased the amount of mixed neutral-acidic mucins relative to P50. Venn analysis identified unique OTUs in the P50 (13), CDCP (74), FM (39), and S50 (31) groups. The protein sources did not change the colonic bacterial richness or diversity. High Escherichia abundance in the P50 and FM, great abundant of Lactobacillus in the CDCP, and high Gemmiger abundance in the S50 were found. The CDCP tended to elevate valeric acid and branched chain fatty acid (BCFA) concentrations compared with the other diets. The P50 and FM groups had greater ammonia nitrogen and methylamine contents than the S50 and CDCP groups. There was a positive correlation between the Escherichia and ammonia nitrogen, the Lactobacillus and short chain fatty acid (SCFA), and a negative correlation between the Gemmige and BCFA. These findings suggested short-term feeding of different protein sources did not affect the piglets' growth, but P50 increased the diarrhea rate. Potential pathogenic bacteria and detrimental metabolites appeared in the colons of piglets fed P50 and FM, whereas, beneficial effects were conferred upon piglets fed CDCP and S50, thus indicating that available plant proteins (cotton seed, soy) added to the diets of piglets enhanced colon health by reducing protein fermentation.

Gut microbiota dysbiosis worsens the severity of acute pancreatitis in patients and mice

BACKGROUND

The gut is implicated in the pathogenesis of acute pancreatitis (AP) and the infectious complications of AP are commonly associated with enteric bacteria, yet whether gut microbiota dysbiosis participants in AP severity remains largely unknown.

METHODS

We collected clinical information and fecal samples from 165 adult participants, including 41 with mild AP (MAP), 59 with moderately severe AP (MSAP), 30 with severe AP (SAP) and 35 healthy controls (HC). The serum inflammatory cytokines and gut barrier indexes were detected. Male C57BL/6 mice with AP were established and injuries of pancreas were evaluated in antibiotic-treated mice, germ-free mice as well as those transplanted with fecal microbiota. The gut microbiota was analyzed by 16S rRNA gene sequencing.

RESULTS

The structure of gut microbiota was significantly different between AP and HC, and the disturbed microbiota was closely correlated with systematic inflammation and gut barrier dysfunction. Notably, the microbial composition changed further with the worsening of AP and the abundance of beneficial bacteria such as Blautia was decreased in SAP compared with MAP and MSAP. The increased capacity for the inferred pathway, bacterial invasion of epithelial cells in AP, highly correlated with the abundance of Escherichia-Shigella. Furthermore, the antibiotic-treated mice and germ-free mice exhibited alleviated pancreatic injury after AP induction and subsequent fecal microbiota transplantation in turn exacerbated the disease.

CONCLUSIONS

This study identifies the gut microbiota as an important mediator during AP and its dysbiosis is associated with AP severity, which suggests its role as potential therapeutic target.

Microbial insight into dietary protein source affects intestinal function of pigs with intrauterine growth retardation

PURPOSE

Dietary protein, as important macronutrient, is vital for intestinal function and health status. We aimed to determine the effects of dietary protein source on growth performance and intestinal function of neonates with intrauterine growth retardation (IUGR) in a pig model.

METHODS

Eighteen pairs of IUGR and normal birth weight (NBW) weaned pigs were allotted to be fed starter diet containing soybean protein concentrate (SPC) or spray-dried porcine plasma (SDPP) for 2 weeks. Growth performance, antioxidant variables, intestinal morphology and absorption capability, microbiota composition and short-chain fatty acids (SCFA) were assessed.

RESULTS

IUGR led to poor growth performance, absorption capability and changes on antioxidant variables, while SDPP diet improved the growth performance, diarrhea index, intestinal morphology and antioxidant variables of IUGR or NBW pigs relative to that fed SPC diet. Importantly, SDPP diet improved bacterial diversity and increased the abundance of phylum Firmicutes, but decreased the phylum Proteobacteria in colonic digesta, associating with higher genera Lactobacillus and lower genera Escherichia-Shigella, linking to the increased concentration of SCFA.

CONCLUSIONS

Our findings indicate that IUGR impairs the growth rate, intestinal function and oxidative status of weaned pigs, which could be partly improved by SDPP diet either for IUGR or NBW pigs, associating with the better antioxidant capability, composition of microbiotas and their metabolites.

Supplementation with α-ketoglutarate to a low-protein diet enhances amino acid synthesis in tissues and improves protein metabolism in the skeletal muscle of growing pigs

α-Ketoglutarate (AKG) is a crucial intermediate in the tricarboxylic acid (TCA) cycle and can be used for the production of ATP and amino acids in animal tissues. However, the effect of AKG on the expression patterns of genes involved in muscle protein metabolism is largely unknown, and the underlying mechanism remains to be elucidated. Therefore, we used young pigs to investigate the effects of a low crude protein (CP) diet and a low CP diet supplemented with AKG on protein accretion in their skeletal muscle. A total of 27 growing pigs with an initial body weight of 11.96 ± 0.18 kg were assigned randomly to one of the three diets: control (normal recommended 20% CP, NP), low CP (17% CP, LP), or low CP supplemented with 1% AKG (ALP). The pigs were fed their respective diets for 35 days. Free amino acid (AA) profile and hormone levels in the serum, and the expression of genes implicated in protein metabolism in skeletal muscle were examined. Results showed that compared with the control group or LP group, low-protein diets supplemented with AKG enhanced serum and intramuscular free AA concentrations, the mRNA abundances of AA transporters, and serum concentrations of insulin-like growth factor-1 (IGF-1), activated the mammalian target of rapamycin (mTOR) pathway, and decreased serum urea concentration and the mRNA levels for genes related to muscle protein degradation (P < 0.05). In conclusion, these results indicated that addition of AKG to a low-protein diet promotes amino acid synthesis in tissues and improves protein metabolism in skeletal muscle.