Dietary and endogenous amino acids are the main contributors to microbial protein in the upper gut of normally nourished pigs

Seasonal variations in composition and function of gut microbiota in grazing yaks: Implications for adaptation to dietary shift on the Qinghai-Tibet plateau

Gut microbiome of animals is affected by external environmental factors and can assist them in adapting to changing environments effectively. Consequently, elucidating the gut microbes of animals under different environmental conditions can provide a comprehensive understanding of the mechanisms of their adaptations to environmental change, with a particular focus on animals in extreme environments. In this study, we compared the structural and functional differences of the gut microbiome of grazing yaks between the summer and winter seasons through metagenomic sequencing and bioinformatics analysis. The results indicated that the composition and function of microbes changed significantly. The study demonstrated an increase in the relative abundance of Actinobacteria and a higher ratio of Firmicutes to Bacteroidetes (F/B) in winter, this process facilitated the adaptation of yaks to the consumption of low-nutrient forages in the winter. Furthermore, the network structure exhibited greater complexity in the winter. Forage nutrition exhibited a significant seasonal variation, with a notable impact on the gut microbiota. The metagenomic analysis revealed an increase in the abundance of enzymes related to amino acid metabolism, axillary activity, and mucin degradation in the winter. In conclusion, this study demonstrated that the gut microbiome of grazing yaks exhibits several adaptive characteristics that facilitate better nutrient accessibility and acid the host in acclimating to the harsh winter conditions. Furthermore, our study offers novel insights into the mechanisms of highland animal adaptation to external environments from the perspective of the gut microbiome.

Nutrient Utilization and Gut Microbiota Composition in Giant Pandas of Different Age Groups

Proper feeding and nutrition are vital for maintaining the health of giant pandas (GPs), yet the impact of dietary changes and gut microbiota on their nutrient utilization remains unclear. To address these uncertainties, we investigated nutrient intake and apparent digestibility, as well as gut microbiota composition across different age groups of giant pandas: sub-adults (SGPs), adults (AGPs), and geriatrics (GGPs). Our findings revealed notable shifts in dietary patterns from SGPs to GGPs. As they aged, significantly more bamboo shoots and less bamboo were consumed. Consequently, GGPs showed significantly reduced crude fiber (CF) intake and digestibility, while crude protein (CP) did not alter significantly. In addition, 16S rRNA microbial sequencing results showed that unidentified_Enterobacteriaceae and Streptococcus were the dominant genera among all age groups. The relative abundance of the genus Enterococcus in GGPs was significantly higher than that in SGPs and AGPs (p < 0.05). Overall, our results indicated the importance of bamboo shoots as a major source of protein in GGPs' diet, which can effectively compensate for the certain nutritional loss caused by the reduction in bamboo intake. Age-related changes in bacterial abundance have an effect on specific nutrient apparent digestibility in the gut of GPs. The data presented in this study serve as a useful reference for nutritional management in different ages of GPs under healthy conditions.

Gut microbiota as a sensor of autoimmune response and treatment for rheumatoid arthritis

Rheumatoid arthritis (RA) is considered a multifactorial condition where interaction between the genetic and environmental factors lead to immune dysregulation causing autoreactivity. While among the various genetic factors, HLA-DR4 and DQ8, have been reported to be the strongest risk factors, the role of various environmental factors has been unclear. Though events initiating autoreactivity remain unknown, a mucosal origin of RA has gained attention based on the recent observations with the gut dysbiosis in patients. However, causality of gut dysbiosis has been difficult to prove in humans. Mouse models, especially mice expressing RA-susceptible and -resistant HLA class II genes have helped unravel the complex interactions between genetic factors and gut microbiome. This review describes the interactions between HLA genes and gut dysbiosis in sex-biased preclinical autoreactivity and discusses the potential use of endogenous commensals as indicators of treatment efficacy as well as therapeutic tool to suppress pro-inflammatory response in rheumatoid arthritis.

Dietary Protein Quality Affects the Interplay between Gut Microbiota and Host Performance in Nile Tilapia

Dietary protein quality plays a key role in maintaining intestinal mucosal integrity, but also modulates the growth of luminal microorganisms. This work assessed the effect of dietary protein sources on the performance, gut morphology, and microbiome in Nile tilapia. Four isonitrogenous and isolipidic diets comprising equivalent amounts of the protein supply derived from either PLANT, ANIMAL, INSECT, or BACTERIAL (bacterial biomass) sources were fed to triplicate groups of fish (IBW: 12 g) for 46 days. Fish fed the ANIMAL and BACTERIAL diets showed significantly higher weight gains than those fed the PLANT and INSECT diets (p < 0.05). Relative abundance at the phylum level showed that Bacteroidetes, Fusobacteria, and Proteobacteria were the more abundant phyla in tilapia's intestine, while Cetobacterium was the most representative genus in all treatments. Interesting patterns were observed in the correlation between amino acid intake and genus and species abundance. Metabolism prediction analysis showed that BACTERIAL amine and polyamine degradation pathways are modulated depending on diets. In conclusion, different protein sources modulate the relationship between bacteria functional pathways and amino acid intake.

Effect of a Bacillus-Based Probiotic on Performance and Nutrient Digestibility When Substituting Soybean Meal with Rapeseed Meal in Grower-Finisher Diets

The objective of the present study was to test the hypothesis of B. subtilis and B. licheniformis supplementation to a negative control diet in comparison to a standard control diet, had the potential to improve the performance and nutrient digestibility of growing-finishing pigs. For this purpose, 384 fattening pigs of 85 d of age were allotted to three treatments: a standard diet, a negative control (NC) diet (5% soybean meal replaced by 5% rapeseed meal), or a NC diet + probiotic. After reaching a body weight of approximately 110 kg, all animals going to the slaughterhouse (87% of total pigs) were selected to measure carcass quality. Moreover, the apparent total tract digestibility of protein was evaluated at the end of the grower period. The results of this study indicate that supplementation of the tested Bacillus-based probiotic significantly improved average daily gain (ADG, +14.6%) and Feed:gain ratio (F:G, -9.9%) during the grower phase compared to the NC diet. The improvement observed during the grower phase was maintained for the whole fattening period (ADG, +3.9%). Probiotic supplementation significantly improved the total apparent faecal digestibility of dry matter and crude protein in pigs at the end of the grower period. The improvements observed with the additive tested could indicate that supplementation of the Bacillus-based probiotic was able to counteract the lower level of crude protein and standardised ileal digestible amino acids in the NC diet by means of improved protein digestibility.

Amino Acid Catabolism: An Overlooked Area of Metabolism

Amino acids have been extensively studied in nutrition, mainly as key elements for maintaining optimal protein synthesis in the body as well as precursors of various nitrogen-containing compounds. However, it is now known that amino acid catabolism is an important element for the metabolic control of different biological processes, although it is still a developing field to have a deeper understanding of its biological implications. The mechanisms involved in the regulation of amino acid catabolism now include the contribution of the gut microbiota to amino acid oxidation and metabolite generation in the intestine, the molecular mechanisms of transcriptional control, and the participation of specific miRNAs involved in the regulation of amino acid degrading enzymes. In addition, molecules derived from amino acid catabolism play a role in metabolism as they are used in the epigenetic regulation of many genes. Thus, this review aims to examine the mechanisms of amino acid catabolism and to support the idea that this process is associated with the immune response, abnormalities during obesity, in particular insulin resistance, and the regulation of thermogenesis.

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 diets with different amino acid release characteristics on the gut microbiota and barrier function of weaned pigs

BACKGROUND

The absorption and utilization of proteins by animals is affected by the amino acid (AA) release characteristics of their diets. In the present study, we aimed to determine the effects of diets with various amino acid release characteristics on the intestinal barrier function and diversity of gut microbiota of weaned pigs.

RESULTS

Forty-eight pigs (7.45 ± 0.58 kg) were fed with diets having different amino acid release characteristics during a period of 28 days. We used a 2 × 3 full-factor (two protein levels and three protein sources with differing amino acid release characteristics) experimental design, with normal (standard terminal ileal digestibility of 17.5%) or low (standard terminal ileal digestibility of 14.9%) protein levels as the first factor. Casein (CAS), corn gluten meal (CGM) and a MIX diet were used as protein sources. Due to the more balanced release of amino acids, the diamine oxidase (DAO) concentrations in the CAS and MIX groups were significantly lower than those in the CGM group (P < 0.05); Reducing the dietary protein content from 17.5% to 14.9% had no significant effects on the levels of serum DAO or D-lactic acid. By contrast, it increased the microbial diversity (chao1 and ACE values) and the number of Lactobacillus in the jejunum (P < 0.05). The CAS-containing diet and the MIX diet resulted in significantly higher microbial diversity (Simpson and Shannon) than the CGM-containing diet in the jejunum.

CONCLUSION

The balanced release of amino acids in CAS and MIX diets maintained intestinal barrier function and increased gut microbiota diversity. These findings could potentially provide a scientific reference for the rational preparation of piglet feed.

Zebrafish: an efficient vertebrate model for understanding role of gut microbiota

Gut microbiota plays a critical role in the maintenance of host health. As a low-cost and genetically tractable vertebrate model, zebrafish have been widely used for biological research. Zebrafish and humans share some similarities in intestinal physiology and function, and this allows zebrafish to be a surrogate model for investigating the crosstalk between the gut microbiota and host. Especially, zebrafish have features such as high fecundity, external fertilization, and early optical transparency. These enable the researchers to employ the fish to address questions not easily addressed in other animal models. In this review, we described the intestine structure of zebrafish. Also, we summarized the methods of generating a gnotobiotic zebrafish model, the factors affecting its intestinal flora, and the study progress of gut microbiota functions in zebrafish. Finally, we discussed the limitations and challenges of the zebrafish model for gut microbiota studies. In summary, this review established that zebrafish is an attractive research tool to understand mechanistic insights into host-microbe interaction.

Selective nourishing of gut microbiota with amino acids: A novel prebiotic approach?

Prebiotics are dietary substrates which promote host health when utilized by desirable intestinal bacteria. The most commonly used prebiotics are non-digestible oligosaccharides but the prebiotic properties of other types of nutrients such as polyphenols are emerging. Here, we review recent evidence showing that amino acids (AA) could function as a novel class of prebiotics based on: (i) the modulation of gut microbiota composition, (ii) the use by selective intestinal bacteria and the transformation into bioactive metabolites and (iii) the positive impact on host health. The capacity of intestinal bacteria to metabolize individual AA is species or strain specific and this property is an opportunity to favor the growth of beneficial bacteria while constraining the development of pathogens. In addition, the chemical diversity of AA leads to the production of multiple bacterial metabolites with broad biological activities that could mediate their prebiotic properties. In this context, we introduce the concept of "Aminobiotics," which refers to the functional role of some AA as prebiotics. We also present studies that revealed synergistic effects of the co-administration of AA with probiotic bacteria, indicating that AA can be used to design novel symbiotics. Finally, we discuss the difficulty to bring free AA to the distal gut microbiota and we propose potential solutions such as the use of delivery systems including encapsulation to bypass absorption in the small intestine. Future studies will need to further identify individual AA, dose and mode of administration to optimize prebiotic effects for the benefit of human and animal health.

Gut microbial response to host metabolic phenotypes

A large number of studies have proved that biological metabolic phenotypes exist objectively and are gradually recognized by humans. Gut microbes affect the host's metabolic phenotype. They directly or indirectly participate in host metabolism, physiology and immunity through changes in population structure, metabolite differences, signal transduction and gene expression. Obtaining comprehensive information and specific identification factors associated with gut microbiota and host metabolic phenotypes has become the focus of research in the field of gut microbes, and it has become possible to find new and effective ways to prevent or treat host metabolic diseases. In the future, precise treatment of gut microbes will become one of the new therapeutic strategies. This article reviews the content of gut microbes and carbohydrate, amino acid, lipid and nucleic acid metabolic phenotypes, including metabolic intermediates, mechanisms of action, latest research findings and treatment strategies, which will help to understand the relationship between gut microbes and host metabolic phenotypes and the current research status.

Interactions between gut microbiota and Parkinson's disease: The role of microbiota-derived amino acid metabolism

Non-motor symptoms (NMS) of Parkinson's disease (PD), such as constipation, sleep disorders, and olfactory deficits, may emerge up to 20 years earlier than motor symptoms. A series of evidence indicates that the pathology of PD may occur from the gastrointestinal tract to the brain. Numerous studies support that the gut microbiota communicates with the brain through the immune system, special amino acid metabolism, and the nervous system in PD. Recently, there is growing recognition that the gut microbiota plays a vital role in the modulation of multiple neurochemical pathways via the “gut microbiota-brain axis” (GMBA). Many gut microbiota metabolites, such as fatty acids, amino acids, and bile acids, convey signaling functions as they mediate the crosstalk between gut microbiota and host physiology. Amino acids' abundance and species alteration, including glutamate and tryptophan, may disturb the signaling transmission between nerve cells and disrupt the normal basal ganglia function in PD. Specific amino acids and their receptors are considered new potential targets for ameliorating PD. The present study aimed to systematically summarize all available evidence on the gut microbiota-derived amino acid metabolism alterations associated with PD.

Effects of alfalfa levels on carcass traits, meat quality, fatty acid composition, amino acid profile, and gut microflora composition of Heigai pigs

Recent years have witnessed a dramatic increase in the demand for healthy and high-quality pork. Alfalfa, one of the most popular perennial forages, is considered a rich source of highly nutritional forage for livestock feed, as it contains over 90% insoluble dietary fiber. Nevertheless, there is a paucity of data confirming the effects of adding alfalfa on pork quality, amino acid composition, and intestinal microbiota composition. Therefore, the objective of this study was to investigate the effects of different dietary levels of alfalfa on carcass traits, meat quality, amino acid and fatty acid composition, and the intestinal microbiota of Heigai pigs. A total of 72 finishing Heigai pigs were randomly assigned to two groups (n = 36), with six replicate groups and six pigs per replication. The two experimental diets were formulated to include graded levels of alfalfa, 20% (AM20) and 30% (AM30). The results showed that adding 30% alfalfa meal did not affect the growth performance of Heigai pigs but significantly reduced backfat thickness (P < 0.05), pH (P < 0.05), increased the a^* value, b^* value, and flavor amino acid and essential amino acid contents in longissimus dorsi muscle (LDM). In addition, AM30 didn't affect colonic microbiota abundance but significantly reduced the relative abundances of three phyla, such as Verrucomicrobia, and 43 genera, such as Akkermansia, and significantly increased the relative abundances of 47 genera, such as Prevotella-2. Overall, these results advocate for a diet containing 30% alfalfa to improve meat quality by changing the intestinal microflora composition without affecting the growth performance of Heigai pigs, which provides compelling evidence for the use of alfalfa to relieve the pressure on corn and soybean meal demand and produce high-quality pork.

Resistant starch: Implications of dietary inclusion on gut health and growth in pigs: a review

Starch from cereal grains, pulse grains, and tubers is a major energy substrate in swine rations constituting up to 55% of the diet. In pigs, starch digestion is initiated by salivary and then pancreatic α-amylase, and has as final step the digestion of disaccharides by the brush-border enzymes in the small intestine that produce monosaccharides (glucose) for absorption. Resistant starch (RS) is the proportion of starch that escapes the enzymatic digestion and absorption in the small intestine. The undigested starch reaches the distal small intestine and hindgut for microbial fermentation, which produces short-chain fatty acids (SCFA) for absorption. SCFA in turn, influence microbial ecology and gut health of pigs. These fermentative metabolites exert their benefits on gut health through promoting growth and proliferation of enterocytes, maintenance of intestinal integrity and thus immunity, and modulation of the microbial community in part by suppressing the growth of pathogenic bacteria while selectively enhancing beneficial microbes. Thus, RS has the potential to confer prebiotic effects and may contribute to the improvement of intestinal health in pigs during the post-weaning period. Despite these benefits to the well-being of pigs, RS has a contradictory effect due to lower energetic efficiency of fermented vs. digested starch absorption products. The varying amount and type of RS interact differently with the digestion process along the gastrointestinal tract affecting its energy efficiency and host physiological responses including feed intake, energy metabolism, and feed efficiency. Results of research indicate that the use of RS as prebiotic may improve gut health and thereby, reduce the incidence of post-weaning diarrhea (PWD) and associated mortality. This review summarizes our current knowledge on the effects of RS on microbial ecology, gut health and growth performance in pigs.

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.

Gastrointestinal Interaction between Dietary Amino Acids and Gut Microbiota: With Special Emphasis on Host Nutrition

The gastrointestinal tract (GIT) of humans and animals is host to a complex community of different microorganisms whose activities significantly influence host nutrition and health through enhanced metabolic capabilities, protection against pathogens, and regulation of the gastrointestinal development and immune system. New molecular technologies and concepts have revealed distinct interactions between the gut microbiota and dietary amino acids (AAs) especially in relation to AA metabolism and utilization in resident bacteria in the digestive tract, and these interactions may play significant roles in host nutrition and health as well as the efficiency of dietary AA supplementation. After the protein is digested and AAs and peptides are absorbed in the small intestine, significant levels of endogenous and exogenous nitrogenous compounds enter the large intestine through the ileocaecal junction. Once they move in the colonic lumen, these compounds are not markedly absorbed by the large intestinal mucosa, but undergo intense proteolysis by colonic microbiota leading to the release of peptides and AAs and result in the production of numerous bacterial metabolites such as ammonia, amines, short-chain fatty acids (SCFAs), branched-chain fatty acids (BCFAs), hydrogen sulfide, organic acids, and phenols. These metabolites influence various signaling pathways in epithelial cells, regulate the mucosal immune system in the host, and modulate gene expression of bacteria which results in the synthesis of enzymes associated with AA metabolism. This review aims to summarize the current literature relating to how the interactions between dietary amino acids and gut microbiota may promote host nutrition and health.

Regulation of Probiotics on Metabolism of Dietary Protein in Intestine

Proteins are indispensable components of living organisms, which are derived mainly from diet through metabolism. Dietary proteins are degraded by endogenous digestive enzymes to di- or tripeptides and free amino acids (AAs) in the small intestine lumen and then absorbed into blood and lymph through intestinal epithelial cells via diverse transporters. Microorganisms are involved not only in the proteins' catabolism, but also the AAs, especially essential AAs, anabolism. Probiotics regulate these processes by providing exogenous proteases and AAs and peptide transporters, and reducing hazardous substances in the food and feed. But the core mechanism is modulating of the composition of intestinal microorganisms through their colonization and exclusion of pathogens. The other effects of probiotics are associated with normal intestinal morphology, which implies that the enterocytes secrete more enzymes to decompose dietary proteins and absorb more nutrients.

Swine gut microbiota and its interaction with host nutrient metabolism

Gut microbiota is generally recognized to play a crucial role in maintaining host health and metabolism. The correlation among gut microbiota, glycolipid metabolism, and metabolic diseases has been well reviewed in humans. However, the interplay between gut microbiota and host metabolism in swine remains incompletely understood. Given the limitation in conducting human experiments and the high similarity between swine and humans in terms of anatomy, physiology, polyphagy, habits, and metabolism and in terms of the composition of gut microbiota, there is a pressing need to summarize the knowledge gained regarding swine gut microbiota, its interplay with host metabolism, and the underlying mechanisms. This review aimed to outline the bidirectional regulation between gut microbiota and nutrient metabolism in swine and to emphasize the action mechanisms underlying the complex microbiome-host crosstalk via the gut microbiota-gut-brain axis. Moreover, it highlights the new advances in knowledge of the diurnal rhythmicity of gut microbiota. A better understanding of these aspects can not only shed light on healthy and efficient pork production but also promote our knowledge on the associations between gut microbiota and the microbiome-host crosstalk mechanism. More importantly, knowledge on microbiota, host health and metabolism facilitates the development of a precise intervention therapy targeting the gut microbiota.

Impact of Fermentable Protein, by Feeding High Protein Diets, on Microbial Composition, Microbial Catabolic Activity, Gut Health and beyond in Pigs

In pigs, high protein diets have been related to post-weaning diarrhoea, which may be due to the production of protein fermentation metabolites that were shown to have harmful effects on the intestinal epithelium in vitro. In this review, we discussed in vivo effects of protein fermentation on the microbial composition and their protein catabolic activity as well as gut and overall health. The reviewed studies applied different dietary protein levels, which was assumed to result in contrasting fermentable protein levels. A general shift to N-utilisation microbial community including potential pathogens was observed, although microbial richness and diversity were not altered in the majority of the studies. Increasing dietary protein levels resulted in higher protein catabolic activity as evidenced by increased concentration of several protein fermentation metabolites like biogenic amines in the digesta of pigs. Moreover, changes in intestinal morphology, permeability and pro-inflammatory cytokine concentrations were observed and diarrhoea incidence was increased. Nevertheless, higher body weight and average daily gain were observed upon increasing dietary protein level. In conclusion, increasing dietary protein resulted in higher proteolytic fermentation, altered microbial community and intestinal physiology. Supplementing diets with fermentable carbohydrates could be a promising strategy to counteract these effects and should be further investigated.

Amino Acids in Intestinal Physiology and Health

Dietary protein digestion is an efficient process resulting in the absorption of amino acids by epithelial cells, mainly in the jejunum. Some amino acids are extensively metabolized in enterocytes supporting their high energy demand and/or production of bioactive metabolites such as glutathione or nitric oxide. In contrast, other amino acids are mainly used as building blocks for the intense protein synthesis associated with the rapid epithelium renewal and mucin production. Several amino acids have been shown to support the intestinal barrier function and the intestinal endocrine function. In addition, amino acids are metabolized by the gut microbiota that use them for their own protein synthesis and in catabolic pathways releasing in the intestinal lumen numerous metabolites such as ammonia, hydrogen sulfide, branched-chain amino acids, polyamines, phenolic and indolic compounds. Some of them (e.g. hydrogen sulfide) disrupts epithelial energy metabolism and may participate in mucosal inflammation when present in excess, while others (e.g. indole derivatives) prevent gut barrier dysfunction or regulate enteroendocrine functions. Lastly, some recent data suggest that dietary amino acids might regulate the composition of the gut microbiota, but the relevance for the intestinal health remains to be determined. In summary, amino acid utilization by epithelial cells or by intestinal bacteria appears to play a pivotal regulator role for intestinal homeostasis. Thus, adequate dietary supply of amino acids represents a key determinant of gut health and functions.

Comparison of methodologies used to define the protein quality of human foods and support regulatory claims

Protein quality (PQ) is the capacity of a protein to meet the amino acid (AA) requirements of an individual. There are several methodologies for determining the PQ of foods. The protein efficiency ratio is an animal growth bioassay. The protein-digestibility-corrected AA score considers the AA requirements of a reference population, and the true nitrogen digestibility coefficient for each ingredient. The digestible indispensable AA score is based on true ileal AA digestibility and better represents bioavailability of AAs. In vitro techniques for assessment of PQ are available but require validation against a greater range of protein sources. Isotopic methods, such as the indicator AA oxidation and dual tracer techniques measure AA relative bioavailability and digestibility, respectively, but require sophisticated equipment, and may not be cost nor time effective for the industry to adopt. The present review discusses advantages and disadvantages of methodologies for determining PQ of food for humans focused on methods that are or could be adopted by regulatory agencies. Understanding the framework and resources available for PQ determination will help in the selection of appropriate methods depending on the application. Novelty Understanding the framework and resources available for PQ determination will help in the selection of appropriate methods depending on the application.

Characterization of urea transport mechanisms in the intestinal tract of growing pigs

Pigs are capable of nitrogen salvage via urea recycling, which involves the movement of urea in the gastrointestinal tract. Aquaporins (AQP) and urea transporter B (UT-B) are involved in urea recycling in ruminants; however, their contribution to urea flux in the intestinal tract of the pig is not known. The objective of this study was to characterize the presence and relative contribution of known urea transporters to urea flux in the growing pig. Intestinal tissue samples (duodenum, jejunum, ileum, cecum, and colon) were obtained from nine barrows (50.8 ± 0.9 kg) and analyzed for mRNA abundance of UT-B and AQP-3, -7, and -10. Immediately after tissue collection, samples from the jejunum and cecum were placed in Ussing chambers for analysis of the serosal-to-mucosal urea flux (Jsm-urea) with no inhibition or when incubated in the presence of phloretin to inhibit UT-B-mediated transport, NiCl2 to inhibit AQP-mediated transport, or both inhibitors. UT-B expression was greatest (P < 0.05) in the cecum, whereas AQP-3, -7, and -10 expression was greatest (P < 0.05) in the jejunum. The Jsm-urea was greater in the cecum than the jejunum (67.8 . 42.7 ± 5.01 µmol·cm-2·h-1; P < 0.05), confirming the capacity for urea recycling in the gut in pigs; however, flux rate was not influenced (P > 0.05) by urea transporter inhibitors. The results of this study suggest that, although known urea transporters are expressed in the gastrointestinal tract of pigs, they may not play a significant functional role in transepithelial urea transport.NEW & NOTEWORTHY We characterized the location and contribution of known urea transporters to urea flux in the pig. Aquaporins are located throughout the intestinal tract, and urea transporter B is expressed only in the cecum. Urea flux occurred in both the jejunum and cecum. Transporter inhibitors had no affect on urea flux, suggesting that their contribution to urea transport in the intestinal tract is limited. Further work is required to determine which factors contribute to urea flux in swine.

Effects of Maternal Low-Protein Diet on Microbiota Structure and Function in the Jejunum of Huzhu Bamei Suckling Piglets

The jejunum is the primary organ for digestion and nutrient absorption in mammals. The development of the jejunum in suckling piglets directly affects their growth performance post-weaning. The jejunum microbiome plays an important role in proliferation, metabolism, apoptosis, immune, and homeostasis of the epithelial cells within the organ. The composition and diversity of the gut microbiome is susceptible to the protein composition of the diet. Therefore, the effects of maternal low-protein diets on piglets' intestinal microbial structure and function have become a hot topic of study. Herein, a maternal low-protein diet was formulated to explore the effects on jejunum microbiome composition and metabolic profiles in Bamei suckling piglets. Using 16S ribosomal RNA (16S rRNA) sequencing in conjunction with bioinformatics analysis, 21 phyla and 297 genera were identified within the gut microflora. The top 10 phyla and 10 genera are within the gut bacteria. Next, KEGG analysis showed that the low-protein diet significantly increased the gut microbial composition, transport and catabolism, immune system, global and overview maps, amino acid metabolism, metabolism of cofactors and vitamins, endocrine system, biosynthesis of other secondary metabolites, signal transduction, environmental adaptation, and cell motility. Taken together, low-protein diets do not appear to affect the reproductive performance of Bamei sows but improved the gut microbiome of the suckling piglets as well as reduced the probability of diarrhea. The data presented here provide new insights on the dietary protein requirements to support the Huzhu Bamei pig industry.

Extraction and identification of the chyme proteins in the digestive tract of growing pigs

This study aimed to explore the rule of degradation of dietary proteins by identifying chyme proteins in different segments of the digestive tract of growing pigs, using proteomics techniques. Six growing pigs were fed a corn-soybean meal-based diet for 7 days. The feedstuff and chyme proteins were separately extracted and separated with SDS-PAGE. 2D LCMS/MS combined with protein database searching identified 1,513 proteins in different segments of the gastrointestinal tract, the number of identified exogenous proteins gradually decline from the stomach to colon, with large amounts in the duodenum to the large intestine. More corn proteins than soybean proteins were identified both in the feedstuff and chyme, and these were significantly decreased after digestion in the stomach. More membrane proteins than non-membrane proteins were identified in whole digestive tract. These results regarding the profiles of chyme proteins in different segments of the gastrointestinal tract would provide useful information for optimizing feed formula in pigs.

Effect of nutritional interventions with quercetin, oat hulls, β-glucans, lysozyme and fish oil on performance and health status related parameters of broilers chickens

1. An experiment was conducted to evaluate the effects of technical feed ingredients between 14 and 28 d of age on performance and health status of broilers (d 14-35) fed diets with a high inclusion rate of rapeseed meal as a nutritional challenge. It was hypothesized that the feed ingredients would improve health status related parameters. 2. A total of 1008 one-day-old male Ross 308 chicks were distributed over 36 floor pens and allocated to one of six iso-caloric (AME_N 13 MJ/kg) growing diets (d 15-28): a control and five test diets supplemented with quercetin (400 mg/kg), oat hulls (50 g/kg), β-glucan (100 mg/kg), lysozyme (40 mg/kg) or fish oil ω-3 fatty acids (40 g/kg), with six replicate pens per treatment. 3. Dietary inclusion of oat hulls and lysozyme resulted in a reduction in broiler performance during the first week after providing the experimental diets. 4. No effect of interventions on the microbiota diversity in the jejunum and ileum was observed. Ileal microbiota composition of birds fed oat hulls differed from the other groups, as shown by a higher abundance of the genus Enterococcus, mainly at the expense of the genus Lactobacillus. 5. In the jejunum, villus height and crypt depth of lysozyme-fed birds at d 28 were decreased compared to the control group. Higher total surface area of villi occupied by goblet cells and total villi surface area in jejunum (d 21 and 28) were observed in chickens fed oat hulls compared to other groups. 6. Genes related to the growth-factor-activity pathway were more highly expressed in birds fed β-glucan compared to the control group, while the genes related to anion-transmembrane-transporter-activity pathway in the quercetin- and oat hull-fed birds were less expressed. The genes differently expressed between dietary interventions did not seem to be directly involved in immune related processes. 7. It was concluded that the tested nutritional interventions in the current experiment only marginally effected health status related parameters.

Advances in low-protein diets for swine

Recent years have witnessed the great advantages of reducing dietary crude protein (CP) with free amino acids (AA) supplementation for sustainable swine industry, including saving protein ingredients, reducing nitrogen excretion, feed costs and the risk of gut disorders without impairing growth performance compared to traditional diets. However, a tendency toward increased fatness is a matter of concern when pigs are fed low-protein (LP) diets. In response, the use of the net energy system and balanced AA for formulation of LP diets has been proposed as a solution. Moreover, the extent to which dietary CP can be reduced is complicated. Meanwhile, the requirements for the first five limiting AA (lysine, threonine, sulfur-containing AA, tryptophan, and valine) that growing-finishing pigs fed LP diets were higher than pigs fed traditional diets, because the need for nitrogen for endogenous synthesis of non-essential AA to support protein synthesis may be increased when dietary CP is lowered. Overall, to address these concerns and give a better understanding of this nutritional strategy, this paper reviews recent advances in the study of LP diets for swine and provides some insights into future research directions.

Black soldier fly defatted meal as a dietary protein source for broiler chickens: Effects on growth performance, blood traits, gut morphology and histological features

BACKGROUND

The present study has evaluated the effects of different inclusion levels of a partially defatted black soldier fly (Hermetia illucens L.; HI) larva meal on the growth performance, blood parameters and gut morphology of broiler chickens. A total of 256 male broiler chickens (Ross 308) were reared from d 1 to d 35 and assigned to 4 dietary treatments (8 replicates/treatment and 8 birds/replicate). HI larva meal was included at increasing levels (0, 5%, 10% and 15%; HI0, HI5, HI10 and HI15, respectively) in isonitrogenous and isoenergetic diets formulated for 3 feeding phases: starter (1-10 d), growing (10-24 d) and finisher (24-35 d). Two birds per pen were slaughtered at d 35 and morphometric investigations and histopathological alterations were performed.

RESULTS

The live weight (LW) showed linear and quadratic responses to increasing HI larva meal (maximum for HI10 group). Average daily gain (ADG) showed a linear and quadratic responses to HI meal (maximum for HI10 group) during starter and growing periods. A linear decrease was observed for ADG during the finisher period. The daily feed intake (DFI) showed a linear and quadratic effect during the starter period (maximum for HI10 group). Linear and quadratic responses were observed for the feed conversion ratio (FCR) in the growing period and for the whole period of the experiment. The FCR showed a linear response in the finisher period (maximum for HI15). No significant effects were observed for the blood and serum parameters, except for the phosphorus concentration, which showed linear and quadratic responses as well as glutathione peroxidase (GPx) activity, the latter of which showed a linear response. The HI15 birds showed a lower villus height, a higher crypt depth and a lower villus height-to-crypt depth ratio than the other groups.

CONCLUSIONS

Increasing levels of dietary HI meal inclusion in male broiler chickens may improve the LW and DFI during the starter period, but may also negatively affect the FCR and gut morphology, thus suggesting that low levels may be more suitable. However, no significant effects on the haematochemical parameters or histological findings were observed in relation to HI meal utilization.

Ammonia Nitrogen Added to Diets Deficient in Dispensable Amino Acid Nitrogen Is Poorly Utilized for Urea Production in Growing Pigs

Background: Including ammonia in low-crude protein (CP) diets deficient in dispensable amino acid (DAAs) increases nitrogen retention in growing pigs.Objective: We investigated the absorption and metabolism of dietary ammonia nitrogen in the portal-drained viscera (PDV) and liver of pigs fed a diet deficient in DAA nitrogen.Methods: Eight pigs with an initial mean ± SD body weight (BW) of 26.5 ± 1.4 kg were surgically fitted with 4 catheters each (portal, hepatic and mesenteric veins, and carotid artery). The pigs were fed (2.8 × 191 kcal/kg BW^0.60), for 7 d and every 8 h, a diet deficient in DAA nitrogen supplemented with increasing amounts of ammonia nitrogen (CP: 7.76%, 9.27%, and 10.77%; indispensable amino acid nitrogen:total nitrogen ratio: 0.71, 0.59, and 0.50 for control and low- and high-ammonia diets, respectively). The treatment sequence was based on a Latin square design with 3 consecutive periods. On the last day of each period, blood flows in the portal and hepatic veins were determined with a continuous infusion of ρ-amino hippuric acid into the mesenteric vein. Serial blood samples were taken to determine ammonia and urea nitrogen concentration. Net balances of ammonia and urea nitrogen were calculated for the PDV and liver.Results: Cumulative (8 h) ammonia nitrogen appearance in the portal vein increased (P ≤ 0.05) with ammonia intake (433, 958, and 1629 ± 60 mg ammonia nitrogen/meal for control and low- and high-ammonia diets, respectively). The cumulative hepatic uptake of ammonia nitrogen increased (P ≤ 0.05) with ammonia nitrogen supply. The cumulative urea nitrogen appearance in the hepatic vein tended to increase (P ≤ 0.10) only in high-ammonia treatment (-92.5, -59.4, and 209.7 ± 92 mg urea nitrogen/meal for control and low- and high-ammonia diets, respectively) and, relative to the control diet, represented -6.0% and 11% of ammonia nitrogen intake.Conclusion: Dietary ammonia nitrogen is poorly utilized for urea production across splanchnic organs when pigs are fed diets deficient in DAA nitrogen.

Low dietary protein and high carbohydrate infant formula affects the microbial ecology of the large intestine in neonatal rats

The aim of this study was to investigate the effects of a low dietary protein and high carbohydrate infant formula on the large intestine of neonatal rats. A total of 24 neonatal Sprague–Dawley rats (14-days-old) were randomly assigned to the low protein, high carbohydrate infant formula-fed group (I group) and a human breast milk-fed group (H group). After 7 days, we selected 6 rats at random from each group to study. No significantly different microbial colonization patterns were observed in the 2 groups at the phylum level. At the family level, Enterobacteriaceae and Bacteroidaceae were the dominant bacteria in I and H rats. While Bacteroides was the most abundant bacteria at the genus level, no significant difference was observed between the 2 groups. Methanoic acid, acetate, and butyrate increased in concentration in the I group compared with the H group. Protease activities, ammonia, and indole in the large intestine were lower in I rats than H rats. A significant increase in the expression of GADPH and decrease in the expression of aquaporin 8, aminopeptidase A, cathepsin F precursor, and ubiquitin carboxyl-terminal hydrolase FAF-Y were observed in I rats compared with H rats. These results suggest that a low protein diet could modulate the microbial ecology in the large intestine of neonatal rats.

Amino Acid Absorption in the Large Intestine of Humans and Porcine Models

Dietary protein quality has been recognized as a critical issue by international authorities because it can affect important functions of the body. To predict protein quality, the FAO introduced the Digestible Indispensable Amino Acid Score. This score depends on ileal amino acid (AA) digestibility; therefore, the assumption is made that AAs are not absorbed in nutritionally relevant amounts from the large intestine. This article reviews the evidence for this assumption by considering the role of the mammalian large intestine in dietary protein and AA digestion and absorption, with particular reference to adult humans. Although most dietary AAs and peptides are absorbed in the small intestine, substantial amounts can enter the large intestine. Nitrogen is absorbed in the large intestine, and a series of animal experiments indicate a potential small degree of AA absorption. In humans, colonocytes have the capacity for AA absorption because AA transporters are present in the large intestine. The absorption of nutritionally relevant amounts of dietary indispensable AAs and peptides in the human large intestine has not been convincingly demonstrated, however.

Effect of Bacillus subtilis and Bacillus licheniformis supplementation in diets with low- and high-protein content on ileal crude protein and amino acid digestibility and intestinal microbiota composition of growing pigs

Background

Bacillus spp. seem to be an alternative to antimicrobial growth promoters for improving animals’ health and performance. However, there is little information on the effect of Bacillus spp. in combination with different dietary crude protein (CP) levels on the ileal digestibility and microbiota composition. Therefore, the objective of this study was to determine the effect of Bacillus spp. supplementation to low- (LP) and high-protein diets (HP) on ileal CP and amino acid (AA) digestibility and intestinal microbiota composition.

Methods

Eight ileally cannulated pigs with an initial body weight of 28.5 kg were randomly allocated to a row-column design with 8 pigs and 3 periods of 16 d each. The assay diets were based on wheat-barley-soybean meal with two protein levels: LP (14% CP, as-fed) and HP diet (18% CP, as-fed). The LP and HP diets were supplemented with or without Bacillus spp. at a level of 0.04% (as-fed). The apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of CP and AA was determined. Bacterial community composition from ileal digesta was analyzed by Illumina amplicon sequencing and quantitative real-time PCR. Data were analyzed as a 2 × 2 factorial design using the GLIMMIX procedures of SAS.

Results

The supplementation with Bacillus spp. did not affect both AID and SID of CP and AA in growing pigs. Moreover, there was no difference in AID of CP and AA between HP and LP diets, but SID of cystine, glutamic acid, glycine, and proline was lower (P < 0.05) in pigs fed the HP diets. The HP diets increased abundance of Bifidobacterium spp. and Lactobacillus spp., (P < 0.05) and by amplicon sequencing the latter was identified as predominant genus in microbiota from HP with Bacillus spp., whereas dietary supplementation of Bacillus spp. increased (P < 0.05) abundance of Roseburia spp..

Conclusions

The HP diet increased abundance of Lactobacillus spp. and Bifidobacterium spp.. The supplementation of Bacillus spp. resulted in a higher abundance of healthy gut associated bacteria without affecting ileal CP and AA digestibility, whereas LP diet may reduce the flow of undigested protein to the large intestine of pigs.

Ontogenetic Differences in Dietary Fat Influence Microbiota Assembly in the Zebrafish Gut

Gut microbiota influence the development and physiology of their animal hosts, and these effects are determined in part by the composition of these microbial communities. Gut microbiota composition can be affected by introduction of microbes from the environment, changes in the gut habitat during development, and acute dietary alterations. However, little is known about the relationship between gut and environmental microbiotas or about how host development and dietary differences during development impact the assembly of gut microbiota. We sought to explore these relationships using zebrafish, an ideal model because they are constantly immersed in a defined environment and can be fed the same diet for their entire lives. We conducted a cross-sectional study in zebrafish raised on a high-fat, control, or low-fat diet and used bacterial 16S rRNA gene sequencing to survey microbial communities in the gut and external environment at different developmental ages. Gut and environmental microbiota compositions rapidly diverged following the initiation of feeding and became increasingly different as zebrafish grew under conditions of a constant diet. Different dietary fat levels were associated with distinct gut microbiota compositions at different ages. In addition to alterations in individual bacterial taxa, we identified putative assemblages of bacterial lineages that covaried in abundance as a function of age, diet, and location. These results reveal dynamic relationships between dietary fat levels and the microbial communities residing in the intestine and the surrounding environment during ontogenesis.

The ability of gut microbiota to influence host health is determined in part by their composition. However, little is known about the relationship between gut and environmental microbiotas or about how ontogenetic differences in dietary fat impact gut microbiota composition. We addressed these gaps in knowledge using zebrafish, an ideal model organism because their environment can be thoroughly sampled and they can be fed the same diet for their entire lives. We found that microbial communities in the gut changed as zebrafish aged under conditions of a constant diet and became increasingly different from microbial communities in their surrounding environment. Further, we observed that the amount of fat in the diet had distinct age-specific effects on gut community assembly. These results reveal the complex relationships between microbial communities residing in the intestine and those in the surrounding environment and show that these relationships are shaped by dietary fat throughout the life of animal hosts.

Estimating fermentative amino acid catabolism in the small intestine of growing pigs

Fermentative catabolism (FAAC) of dietary and endogenous amino acids (AA) in the small intestine contributes to loss of AA available for protein synthesis and body maintenance functions in pigs. A continuous isotope infusion study was performed to determine whole body urea flux, urea recycling and FAAC in the small intestine of ileal-cannulated growing pigs fed a control diet (CON, 18.6% CP; n=6), a high fibre diet with 12% added pectin (HF, 17.7% CP; n = 4) or a low-protein diet (LP, 13.4% CP; n = 6). (15)N-ammonium chloride and (13)C-urea were infused intragastrically and intravenously, respectively, for 4 days. Recovery of ammonia at the distal ileum was increased by feeding additional fibre when compared with the CON (P > 0.05) but was not affected by dietary protein (0.24, 0.39 and 0.14 mmol nitrogen/kg BW/day for CON, HF and LP, respectively; P < 0.05). Lowering protein intake reduced urea flux (25.3, 25.7 and 10.3 mmol nitrogen/kg BW/day; P < 0.01), urinary urea excretion (14.4, 15.0 and 6.2 mmol N/kg BW/day; P < 0.001) and urea recycling (12.1, 11.3 and 3.23 mmol nitrogen/kg BW/day; P< 0 .01) compared with CON. There was a rapid reduction in (15)N-ammonia enrichment in digesta along the small intestine suggesting rapid absorption of ammonia before the distal ileum and lack of uniformity of enrichment in the digesta ammonia pool. A two-pool model was developed to determine possible value ranges for nitrogen flux in the small intestine assuming rapid absorption of ammonia.Maximum estimated FAAC based on this model was significantly lower when dietary protein content was decreased (32.9, 33.4 and 17.4 mmol nitrogen/kg BW/day; P < 0.001). There was no impact of dietary fibre on estimates of small intestine nitrogen flux( P > 0.05)compared with CON. The two-pool model developed in the present study allows for estimation of FAAC but still has limitations. Quantifying FAAC in the small intestine of pigs, as well as other non-ruminants and humans, offers a number of challenges but warrants further investigation.

[Microbiome and nutrition. The way to a future therapy for chronic inflammatory bowel diseases?]

The complex microbiome of the human gut contains an excessive amount of genetic information that is more than 100-fold larger than the human genome. In patients with inflammatory bowel disease diversity of the gut microbiome is significantly reduced and moreover specific phyla are overrepresented or underrepresented. However, the functional capacity of the microflora to generate certain metabolic products containing lipids or amino acids- and more complex regulatory substances is more important that the mere annotation of the microorganisms. Modern pharmacological approaches target the functional capacity and constitution of the microbiome. An important strategy is the development of controlled release formulations that deliver defined lipid, carbohydrate or amino acid products derived from nutritional components targeting gut areas distal to the absorption zones of the upper gastrointestinal tract.

Important impacts of intestinal bacteria on utilization of dietary amino acids in pigs

Bacteria in pig intestine can actively metabolize amino acids (AA). However, little research has focused on the variation in AA metabolism by bacteria from different niches. This study compared the metabolism of AA by microorganisms derived from the lumen and epithelial wall of the pig small intestine, aiming to test the hypothesis that the metabolic profile of AA by gut microbes was niche specific. Samples from the digesta, gut wall washes and gut wall of the jejunum and ileum were used as inocula. Anaerobic media containing single AA were used and cultured for 24 h. The 24-h culture served as inocula for the subsequent 30 times of subcultures. Results showed that for the luminal bacteria, all AA concentrations except phenylalanine in the ileum decreased during the 24-h in vitro incubation with a increase of ammonia concentration, while 4 AA (glutamate, glutamine, arginine and lysine) in the jejunum decreased, with the disappearance rate at 60-95 %. For tightly attached bacteria, all AA concentrations were generally increased during the first 12 h and then decreased coupled with first a decrease and then an increase of ammonia concentration, suggesting a synthesis first and then a catabolism pattern. Among them, glutamate in both segments, histidine in the jejunum and lysine in the ileum increased significantly during the first 12 h and then decreased at 24 h. The concentrations of glutamine and arginine did not change during the first 12 h, but significantly decreased at 24 h. Jejunal lysine and ileal threonine were increased for the first 6 or 12 h. For the loosely attached bacteria, there was no clear pattern for the entire AA metabolism. However, glutamate, methionine and lysine in the jejunum decreased after 24 h of cultivation, while glutamine and threonine in the jejunum and glutamine and lysine in the ileum increased in the first 12 h. During subculture, AA metabolism, either utilization or synthesis, was generally decreased with disappearance rate around 20-40 % for most of AA and negligible for branch chained AA (BCAA). However, the disappearance rate of lysine in each group was around 90 % throughout the subculture, suggesting a high utilization of lysine by bacteria from all three compartments. Analysis of the microbial community during the 24-h in vitro cultivation revealed that bacteria composition in most AA cultures varied between different niches (lumen and wall-adherent fractions) in the jejunum, while being relatively similar in the ileum. However, for isoleucine and leucine cultures, bacteria diversity was similar between the luminal fraction and tightly attached fraction, but significantly higher than in the loosely attached fraction. For glutamine and valine cultures, bacteria diversity was similar between the luminal and loosely attached fractions, but lower than that of tightly attached bacteria. After 30 subcultures, bacteria diversity in arginine, valine, glutamine, and leucine cultures varied between niches in the jejunum while being relatively stable in the ileum, consistent with those in the 24-h in vitro cultures. The findings may suggest that luminal bacteria tended to utilize free AA, while tightly attached adherent bacteria seemed in favor of AA synthesis, and that small intestinal microbes contributed little to BCAA metabolism.

Nonprotein nitrogen is absorbed from the large intestine and increases nitrogen balance in growing pigs fed a valine-limiting diet

Nitrogen absorption from the large intestine, largely as ammonia and possibly as amino acids (AAs), is generally thought to be of little nutritional value to nonruminant animals and humans. Ammonia-nitrogen absorbed from the large intestine, however, may be recycled into the small intestine as urea and incorporated into microbial AAs, which may then be used by the host. A cecal infusion study was performed to determine the form in which nitrogen is absorbed from the large intestine and the impact of large intestine nitrogen supply on nitrogen balance in growing pigs. Eighteen cecally cannulated barrows (initial body weight: 22.4 ± 1.2 kg) were used to determine the effect of supplying nitrogen into the large intestine from either casein or urea on whole-body nitrogen retention and urea kinetics. Treatments were cecal infusions of saline (control), casein, or urea with nitrogen infused at a rate of 40% of nitrogen intake. In a subsample of 9 pigs, (15)N(15)N-urea was infused via i.v. during the nitrogen-balance period to determine urea kinetics. All pigs were fed a valine-limiting cornstarch-soybean meal-based diet. More than 80% of infused nitrogen was apparently absorbed. Urea flux and urinary nitrogen excretion increased (P ≤ 0.05) by the same amount for both nitrogen sources, but this increase did not fully account for the increase in nitrogen absorption from the large intestine. Whole-body nitrogen retention improved with nitrogen infusions (129 vs. 114 g/d; P < 0.01) and did not differ (P > 0.05) between nitrogen sources. Absorption of nitrogen from the large intestine appears to be in the form of nonprotein nitrogen, which appears to be returned to the small intestine via urea and used there for microbial AA production and should therefore be considered when determining nitrogen and AA supply and requirements.

Re-print of "Intestinal luminal nitrogen metabolism: role of the gut microbiota and consequences for the host"

Alimentary and endogenous proteins are mixed in the small intestinal lumen with the microbiota. Although experimental evidences suggest that the intestinal microbiota is able to incorporate and degrade some of the available amino acids, it appears that the microbiota is also able to synthesize amino acids raising the view that amino acid exchange between the microbiota and host can proceed in both directions. Although the net result of such exchanges remains to be determined, it is likely that a significant part of the amino acids recovered from the alimentary proteins are used by the microbiota. In the large intestine, where the density of bacteria is much higher than in the small intestine and the transit time much longer, the residual undigested luminal proteins and peptides can be degraded in amino acids by the microbiota. These amino acids cannot be absorbed to a significant extent by the colonic epithelium, but are precursors for the synthesis of numerous metabolic end products in reactions made by the microbiota. Among these products, some like short-chain fatty acids and organic acids are energy substrates for the colonic mucosa and several peripheral tissues while others like sulfide and ammonia can affect the energy metabolism of colonic epithelial cells. More work is needed to clarify the overall effects of the intestinal microbiota on nitrogenous compound metabolism and consequences on gut and more generally host health.

Determination of protein and amino acid digestibility in foods including implications of gut microbial amino acid synthesis

To meet the protein and amino acid requirements of individuals and of populations requires information not only about their requirements but also about the capacity of available foods to meet those requirements. Most of our current knowledge of the digestibility of food proteins and the methods to estimate it has been derived from work with animals. Because the microbiota of the large intestine alter the amino acid composition of the digesta, and because only trivial quantities of amino acids are absorbed intact from the large intestine, the current method of choice for assessing amino acid digestibility is ileal digestibility corrected for basal endogenous losses, that is, standardized ileal digestibility. For protein as a whole, however, because nitrogen absorbed in forms other than as amino acids can contribute to the nitrogen economy, the absorption of nitrogen over the whole digestive tract is the more appropriate measure. Most of the methods developed for estimating ileal amino acid outflow in animals are not directly applicable to man: the exception is the use of volunteers with an ileostomy. The flow and composition of ileal digesta in human subjects can also be measured by the infusion of a marker and withdrawal of samples through a naso-intestinal tube. However, this method is too demanding for routine use and is likely to be restricted to validating the application to humans of digestibility data obtained either from animals, of which the pig seems most suitable, orin vitromethods. Microbial activity in the gastrointestinal (GI) tract is not confined to the large intestine: the numbers and metabolic activity of the upper GI microbiota lead to substantial amounts of microbial protein leaving the ileum. It appears however that a large proportion of the amino acids used by the upper GI microbiota are preformed - from the diet or from endogenous materials - rather than fromde novosynthesis. Although there are still uncertainties about the impact of microbial activity in the upper GI tract, the amino acid composition of ileal digesta provides the best available basis for estimating the proportion of dietary amino acids available for metabolism.

Evidence for validity of ileal digestibility coefficients in monogastrics

Measures of amino acid (AA) digestibility are used widely to estimate bioavailability of AA in feed and food ingredients for monogastric animals. In principle, the digestibility assay is simpler thanin vivoassessments of AA bioavailability and allows for simultaneous estimation of the bioavailability of all AA in an experimental diet. It is generally assumed that absorption of intact AA in the hindgut of monogastrics is minimal, even though colonocytes do contain AA transporters and have been shown to absorb AA. This assumption is supported by the observation that infusion of AA into the hindgut does not improve nitrogen balance in monogastrics. In addition, growth performance of monogastrics is more highly correlated with ileal than faecal AA digestibility. Therefore, ileal digestibility coefficients provide better estimates of AA bioavailability than faecal digestibility coefficients. Measures of apparent ileal digestibility (AID) of AA are confounded with endogenous gut AA losses (EAAL). The curvilinear increase in AID of AA with increasing dietary AA level has been attributed to the relatively large contribution of EAAL to total ileal AA flows at low dietary AA levels. Subtracting basal EAAL from total ileal AA flows yields standardized ileal digestibility (SID) coefficients that appear to be more additive than AID coefficients in mixtures of feed ingredients. An implicit assumption when using SID AA coefficients in diet formulation is that the post-absorptive utilization of AA is not influenced by the dietary protein source. This assumption appears inappropriate when using feed or food ingredients that have been over-heated, induce large amounts of EAAL, or contain substantial amounts of fermentable fibre. Improved understanding of processes that contribute to the discrepancy between bioavailability and ileal digestibility will allow a more effective use of AA digestibility coefficients in diet formulation.

Metabolism of select amino acids in bacteria from the pig small intestine

This study investigated the metabolism of select amino acids (AA) in bacterial strains (Streptococcus sp., Escherichia coli and Klebsiella sp.) and mixed bacterial cultures derived from the jejunum and ileum of pigs. Cells were incubated at 37°C for 3 h in anaerobic media containing 0.5-5 mM select AA plus [U-14C]-labeled tracers to determine their decarboxylation and incorporation into bacterial protein. Results showed that all types of bacteria rapidly utilized glutamine, lysine, arginine and threonine. However, rates of the utilization of AA by pure cultures of E. coli and Klebsiella sp. were greater than those for mixed bacterial cultures or Streptococcus sp. The oxidation of lysine, threonine and arginine accounted for 10% of their utilization in these pure bacterial cultures, but values were either higher or lower in mixed bacterial cultures depending on AA, bacterial species and the gut segment (e.g., 15% for lysine in jejunal and ileal mixed bacteria; 5.5 and 0.3% for threonine in jejunal mixed bacteria and ileal mixed bacteria, respectively; and 20% for arginine in ileal mixed bacteria). Percentages of AA used for bacterial protein synthesis were 50-70% for leucine, 25% for threonine, proline and methionine, 15% for lysine and arginine and 10% for glutamine. These results indicate diverse metabolism of AA in small-intestinal bacteria in a species- and gut compartment-dependent manner. This diversity may contribute to AA homeostasis in the gut. The findings have important implications for both animal and human nutrition, as well as their health and well-beings.

Nutrition and health relevant regulation of intestinal sulfur amino acid metabolism

Sulfur amino acids (SAA), particularly methionine and cysteine, are critical for the gut to maintain its functions including the digestion, absorption and metabolism of nutrients, the immune surveillance of the intestinal epithelial layer and regulation of the mucosal response to foreign antigens. However, the metabolism of SAA in the gut, specifically the transmethylation of methionine, will result in a net release of homocysteine, which is shown to be associated with cardiovascular disease and stroke. Furthermore, the extensive catabolism of dietary methionine by the intestine or by luminal microbes may result in a decrease in nutritional efficiency. Therefore, the regulation of SAA metabolism in the gut is not only nutritionally relevant, but also relevant to the overall health and well-being. The superiority of DL-2-hydroxy-4-methylthiobutyrate to DL-methionine in decreasing homocysteine production, alleviating stress responses, and reducing the first-pass intestinal metabolism of dietary methionine may provide a promising implication for nutritional strategies to manipulate SAA metabolism and thus to improve the nutrition and health status of animals and perhaps humans.