Dietary protein-bound or free amino acids differently affect intestinal morphology, gene expression of amino acid transporters, and serum amino acids of pigs exposed to heat stress

Effects of Shrimp Shell-Derived Chitosan on Growth, Immunity, Intestinal Morphology, and Gene Expression of Nile Tilapia (Oreochromis niloticus) Reared in a Biofloc System

Chitosan (CH) shows great potential as an immunostimulatory feed additive in aquaculture. This study evaluates the effects of varying dietary CH levels on the growth, immunity, intestinal morphology, and antioxidant status of Nile tilapia (Oreochromis niloticus) reared in a biofloc system. Tilapia fingerlings (mean weight 13.54 ± 0.05 g) were fed diets supplemented with 0 (CH0), 5 (CH5), 10 (CH10), 20 (CH20), and 40 (CH40) mL·kg-1 of CH for 8 weeks. Parameters were assessed after 4 and 8 weeks. Their final weight was not affected by CH supplementation, but CH at 10 mL·kg-1 significantly improved weight gain (WG) and specific growth rate (SGR) compared to the control (p < 0.05) at 8 weeks. Skin mucus lysozyme and peroxidase activities were lower in the chitosan-treated groups at weeks 4 and 8. Intestinal villi length and width were enhanced by 10 and 20 mL·kg-1 CH compared to the control. However, 40 mL·kg-1 CH caused detrimental impacts on the villi and muscular layer. CH supplementation, especially 5-10 mL·kg-1, increased liver and intestinal expressions of interleukin 1 (IL-1), interleukin 8 (IL-8), LPS-binding protein (LBP), glutathione reductase (GSR), glutathione peroxidase (GPX), and glutathione S-transferase (GST-α) compared to the control group. Overall, dietary CH at 10 mL·kg-1 can effectively promote growth, intestinal morphology, innate immunity, and antioxidant capacity in Nile tilapia fingerlings reared in biofloc systems.

The protective effect of L-theanine on the intestinal barrier in heat-stressed organisms

Heat stress caused by heatwaves, extreme temperatures, and other weather can damage the intestinal barrier of organisms. L-Theanine (LTA) attenuates heat stress-induced oxidative stress, inflammatory responses, and impaired immune function, but its protective effect on the intestinal barrier of heat-stressed organisms is unclear. In this study, low (100 mg kg-1 d-1), medium (200 mg kg-1 d-1), and high (400 mg kg-1 d-1) dosages of LTA were used in the gavage of C57BL/6J male mice that were experimented on for 50 d. These mice were subjected to heat stress for 2 h d-1 at 40 ± 1 °C and 60 ± 5% RH in the last 7 d. LTA attenuated the heat stress-induced decreases in body mass and feed intake, and the destruction of intestinal villi and crypt depth; reduced the serum levels of FITC-dextran and D-LA, as well as the DAO activity; and upregulated the colonic tissues of Occludin, Claudin-1, and ZO-1 mRNA and occludin protein expression. The number of goblet cells in the colon tissue of heat-stressed organisms increased in the presence of LTA, and the expression levels of Muc2, Muc4 mRNA, and Muc2 protein were upregulated. LTA increased the abundance of Bifidobacterium and Turicibacter, and decreased the abundance of Enterorhabdus and Desulfovibrio in the intestinal tract of heat-stressed organisms and restored gut microbiota homeostasis. LTA promoted the secretion of IL-4, IL-10, and sIgA and inhibited the secretion of TNF-α and IFN-γ in the colon of heat-stressed organisms. The expressions of Hsf1, Hsp70, Hsph1, TLR4, P38 MAPK, p-P65 NF-κB, MLCK mRNA, and proteins were downregulated by LTA in the colon of heat-stressed organisms. These results suggest that LTA protects the intestinal barrier in heat-stressed organisms by modulating multiple molecular pathways. Therefore, this study provides evidence on how tea-containing LTA treatments could be used to prevent and relieve intestinal problems related to heat stress.

Insights into the functional properties of a natural free amino acid mix: Effect on growth performance, nutrient metabolism, and immune response in a carnivorous fish, Asian seabass (Lates calcarifer)

Dietary supplements containing a functional feed additive have been shown to be beneficial to fish and shellfish aquaculture. However, the functional properties of aquafeed formulations have rarely been reported in fish. This study aimed to investigate the effects of natural free amino acid mix (FAAM) supplementation as a functional solution on the growth performance and nutrient utilization in a carnivorous fish, Asian seabass (Lates calcarifer). Five isonitrogenous and isolipidic diets were prepared with graded supplementation levels of FAAM at 0 % (control group), 0.25 %, 0.50 %, 0.75 %, and 1.0 %, denoted as FAAM0, FAAM0.25, FAAM0.5, FAAM0.75, and FAAM1.0, respectively. The experimental fish were fed different dietary FAAM supplementations to apparent satiation twice daily for eight weeks. Significant improvements were observed in the growth performance of fish among the five groups (P < 0.05). Fish fed with FAAM0.75 displayed significantly increased activities of lysozyme, myeloperoxidase, catalase, and glutathione peroxidase (P < 0.05). The activities of digestive enzymes, including amylase, protease, and lipase, were enhanced by the supplementation of FAAM in the feed (P < 0.05), especially for the groups that contained more than 0.5 % FAAM in the feed. Furthermore, the morphological profile of the intestinal tract, including the mucosal fold height, width, thickness, and goblet cell, increased in fish fed with FAAM at 1.0 % (P < 0.05). Moreover, FAAM supplementation in diets not only modulated the expression of immune-related genes (glutathione peroxidase (GPx), complement (C)3, C4, and C-reactive protein) in the liver but also positively impacted the growth-ralated genes, including growth hormone (GH), GH receptor (GHR), insulin-like growth factor I (IGF-I), and IGF-II. In addition, the amounts of monounsaturated fatty acids (mainly oleic acid (C18:1n9c)) and polyunsaturated fatty acids-especially γ-linolenic acid (C18:3 n6) and α-linolenic acid (C18:3n3)-increased in fish fed with diets containing FAAMs (P < 0.05). Interestingly, the diets supplemented with FAAMs also had a positive effect on the economic indices in terms of revenue-to-cost ratios. These findings provide a scientific basis for the application of FAAMs as a functional solution that can be used in feed formulations for Asian seabass.

L-Tryptophan Differentially Regulated Glucose and Amino Acid Transporters in the Small Intestine of Rat Challenged with Lipopolysaccharide

Tryptophan (Trp) has been shown to improve the growth and gut function of weaned piglets. Whether the growth-promoting effect of Trp is due to the improvement in nutrient transport and absorption during weaning or under conditions of inflammation has not been fully characterized. The objective of this study was to determine the effects of Trp on lipopolysaccharide (LPS)-induced changes in glucose and amino acid (AA) transport in the rat jejunum. Twenty-four 7-week-old Sprague Dawley rats were randomly divided into one of three groups: control, LPS, and Trp + LPS. Rats were supplemented with 0 or 0.1 mg Trp per gram body weight/d in drinking water for 7 days and were intraperitoneally injected with LPS (5 mg/kg BW) on day 8. After 24 h, rats were sacrificed, and jejunum samples were isolated for the analysis of glucose and AA transport using an Ussing chamber and the expression of glucose and AA transporters. The results showed that Trp alleviated the LPS-induced increase in jejunal permeability (p < 0.05) and decrease in changes in the short-circuit current of glucose, arginine, glutamine, glutamate, glycine, histidine, leucine, lysine, taurine, threonine, and Trp (p < 0.05). Trp reversed (p < 0.05) the LPS-induced downregulation of expression of the glucose transporter SGLT1 and AA transporters solute carrier family 38 member 2 (SNAT2) and solute carrier family 7 member 8 (LAT2), as well as ATPase Na+/K+ transporting subunit alpha 2 (ATP1A2). However, Trp increased (p < 0.01) the LPS-induced upregulation of acidic AA transporter solute carrier family 1 member 1 (EAAT3) expression. The above findings may help to develop nutritional interventions for the differential targeting of gut nutrient transporters, aiming to improve gut function and health in the presence of inflammation in both humans and animals.

Heat stress-induced intestinal barrier damage and dimethylglycine alleviates via improving the metabolism function of microbiota gut brain axis

Heat stress, a widely occurred in subtropical climate regions, causes ecosystem destruction, and intestine injury in humans and animals. As an important compound in the metabolic pathway of choline, dimethylglycine (DMG) shows anti-inflammatory effects. This study examines the beneficial effects of dietary DMG against heat stress-induced intestine injury and further explores the underlying molecular mechanisms using a broiler model. Here, we showed that DMG supplements exhibited positive effects to growth performance, as evidenced by the significantly increased body weight and feed conversion rate. These therapeutic effects attributed to repaired gut barrier integrity, increased content of anti-inflammatory cytokines IL-10, decreased content of pro-inflammatory cytokines IL-6, and down-regulated gene expression of the NF-κB signaling pathway. DMG treatment led to the reshaping of the gut microbiota composition, mainly increasing the short-chain fatty acid (SCFAs) strains such as Faecalibacterium, and Marvinbryantia. DMG treatment also increased two main members of SCFAs, including acetate acid and isobutyrate. Particularly, distinct effects were found which mediated the tryptophan metabolism in intestines such as increased tryptophan and 5-HT, which further alleviate the occurrence of intestinal barrier damage caused by heat stress. Additionally, DMG treatment promoted neuroendocrine function and stimulated the hypothalamic neurotransmitter metabolism by activating tryptophan metabolism in the hypothalamus. Overall, DMG supplementation effectively reduced the occurrence of intestinal inflammation induced by heat stress through modulating cecal microbial communities and improving the metabolism function of microbiota gut brain axis. Our findings revealed a novel mechanism by which gut microbiota could improve host health.

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

With the growing global demand for animal protein and rising temperatures caused by climate change, heat stress (HS) is one of the main emerging environmental challenges for the poultry industry. Commercially-reared birds are particularly sensitive to hot temperatures, so adopting production systems that mitigate the adverse effects of HS on bird performance is essential and requires a holistic approach. Feeding and nutrition can play important roles in limiting the heat load on birds; therefore, this review aims to describe the effects of HS on feed intake (FI) and nutrient digestibility and to highlight feeding strategies and nutritional solutions to potentially mitigate some of the deleterious effects of HS on broiler chickens. The reduction of FI is one of the main behavioral changes induced by hot temperatures as birds attempt to limit heat production associated with the digestion, absorption, and metabolism of nutrients. Although the intensity and length of the heat period influences the type and magnitude of responses, reduced FI explains most of the performance degradation observed in HS broilers, while reduced nutrient digestibility appears to only explain a small proportion of impaired feed efficiency following HS. Targeted feeding strategies, including feed restriction and withdrawal, dual feeding, and wet feeding, have showed some promising results under hot temperatures, but these can be difficult to implement in intensive rearing systems. Concerning diet composition, feeding increased nutrient and energy diets can potentially compensate for decreased FI during HS. Indeed, high energy and high crude protein diets have both been shown to improve bird performance under HS conditions. Specifically, positive results may be obtained with increased added fat concentrations since lipids have a lower thermogenic effect compared to proteins and carbohydrates. Moreover, increased supplementation of some essential amino acids can help support increased amino acid requirements for maintenance functions caused by HS. Further research to better characterize and advance these nutritional strategies will help establish economically viable solutions to enhance productivity, health, welfare, and meat quality of broilers facing HS.

Interactive effects of dietary amino acid density and environmental temperature on growth performance and expression of selected amino acid transporters, water channels, and stress-related transcripts

Exposure to heat stress (HS) is one of the challenges facing the broiler industry worldwide. Various nutritional strategies have been suggested, such as altering dietary concentrations of some nutrients. Thus, we evaluated feeding different amino acid (AA) densities on live performance, Pectoralis (P.) muscles, and expression of selected AA transporters, water channels, and stress-related transcripts in a fast-growing broiler strain. Ross 308 chicks (n = 576) were randomly assigned to 4 dietary treatments (24 reps, 6 chicks per rep), differing in AA density (110, 100, 90, and 80% of a breeder's AA specifications). During 24 to 36 days of age, half of the birds were kept at a thermoneutral (TN) temperature of 20°C, whereas the other half were subjected to HS at 32° C for 8 h daily, making the treatment design a 4 × 2. The results revealed no interaction between housing temperature and AA density on growth performance or P. muscles weights. Feeding 80% AAs depressed BWG, FCR, and P. muscles at 36 d (P < 0.001). There was an interaction (P < 0.001) between AA density and temperature on the expression of all examined genes. Reducing the AA density beyond 100% upregulated the expression of AA transporter (CAT1, B⁰AT, b^0,+AT, SNAT1, LAT1), HSP70, HSP90, glucocorticoid receptor (GR), and AQP3 in the TN birds’ jejunum. Whereas in the HS birds, inconsistent expressions were observed in the jejunum, of which CAT1, B⁰AT, and LAT1 were markedly downregulated as AA density was reduced. In P. major of TN birds, reducing AA density resulted in upregulating the expression of all AA transporters, HSP70, GR, and AQP1, while downregulating HSP90 and AQP9. In contrast, AA reduction markedly downregulated CAT1, B⁰AT, and LAT1 in the P. major of HS birds. These findings indicate that the dietary AA level alters the expression of various genes involved in AA uptake, protein folding, and water transport. The magnitude of alteration is also dependent on the housing temperature. Furthermore, the results highlight the importance of adequate AA nutrition for fast-growing chickens under HS.

Effects of Heat Stress on Gut Microbiome in Rats

Gut microbiome, as the largest and most important micro-ecosystem, plays a critical role in health. The purpose of this study was to evaluate whether heat stress modulates the composition and diversity of the gut microbiome in rats. The heat stress model was prepared in rats with the heating temperature maintained at 35–38°C. Cecum contents were collected after heat stress for 3 h and days 1, 3 and 7. Total DNA was extracted for 16 S rRNA sequencing and analysis of intestinal microbiome composition and diversity. The study showed that the composition of the intestinal microbiome of heat stress group was changed. And the heat stress modulated key phylotypes of gut microbiota at the level of phylum and genus. In particular, the genus of Lactobacillus and Bacteroides were significantly reduced, whereas the Oscillospira and Clostridium were increased by heat stress. Meanwhile, the rats under the heat stress encountered the change in carbohydrate metabolism, amino acid metabolism, and membrane transport to defense against stress. Taken together, the composition and structure of gut microbiome were affected by heat stress and some key phylotypes were also significantly altered. We conclude that the heat stress could impact multiple biological functions, via altering the gut microbiome.