Ahmad Salahi

Unlike mammals, birds lack canonical brown adipose tissue and the UCP1 gene, yet exhibit UCP1-independent non-shivering thermogenesis (NST). In vitro, embryonic chicken mesenchymal cells differentiate into avian brown adipocyte-like cells (ABALCs) with multilocular lipid droplets, elevated mitochondrial density, and upregulated PGC-1α and PPARγ, activating a transfected mouse UCP1 promoter despite endogenous UCP1 loss. In vivo, gradual cold acclimatization or triiodothyronine (T 3) induces beige-like adipocytes enriched in mitochondria within the subcutaneous neck depot ("neck warmer"), with increased avian uncoupling protein (avUCP), CIDEA, TBX1, and mitochondrial markers, while abdominal fat remains largely unresponsive. Skeletal muscle is the main site of NST, where SERCA/RyR-mediated calcium cycling and avUCP/ANT-associated mitochondrial uncoupling are candidate mechanisms; because avUCP is multifunctional (heat, redox and fuel handling), its expression is not by itself a read-out of heat output. Nutritional and microbial interventions-including polyunsaturated fatty acids, capsaicin, succinate, bile acids, and probiotics-have been associated with altered lipid metabolism and reduced visceral adiposity, although direct links to quantifiable heat production remain unestablished and non-thermogenic mechanisms (lipid digestion, hepatic lipogenesis, feed intake, inflammation) have not been excluded. Collectively, the evidence is consistent with, but does not yet prove, a conserved, multi-organ thermogenic metabolic network (TMN) in birds in which skeletal muscle predominates. Exploiting this latent capacity offers a conceptual framework for nutritional and management strategies to mitigate excessive fat deposition and enhance thermal resilience in commercial broilers, although the energetic trade-offs with growth and feed efficiency remain to be resolved. A structured roadmap integrating nutritional, microbial, environmental, and genetic approaches is proposed to test, and if validated to harness, the TMN for sustainable production.

Wheat bran (WB), but also hulls from rice, oat, sunflower and soybean, wood chips, and industrial fiber byproducts are among the main sources of insoluble fiber in poultry nutrition. Insoluble fiber (IF) in poultry is more than a diet-diluent because of it improves performance, digestive tract ecology, and health in poultry. Feeding of 2.5-3.5% of IF could improve feed efficiency and nutrient digestibility, whereas soluble dietary fiber (SDF) causes increased viscosity, intestinal transit time, and decreased feed intake, digestibility, and growth rate. The nutritional advantages of WB include the high fiber (48-53%), protein (9.6-18.6%), vitamin B, betaine, and minerals, as well as the improvement of health status and production. Microbial fermentation is utilized to enhance the nutritional properties of wheat bran fiber by incorporating fungi, bacteria, and yeast. Wheat bran, rich in dietary fiber microorganisms like Aspergillus, Saccharomyces, Lactobacillus, and Bacillus. Used in fermentation process under controlled conditions (temperature, pH, oxygen, and moisture levels) promote microbial growth, improves nutrient content, digestibility, and gastrointestinal health, making wheat bran a valuable feed ingredient for poultry nutrition. The main challenge of WB feeding is due to its high fiber content, anti-nutritional factors affecting the digestion and absorption of nutrients, intestinal viscosity, and microbiota. Diets diluted with WB affect the amount of endogenous and exogenous enzymes, intestinal length and relative weight of the gizzard. Intrinsic phytase is one of the less discussed advantages of WB in monogastric nutrition; it increases the bioavailability of phosphorus and several other nutrients and reduces the need to add exogenous phytase and phosphate sources. Endogenous WB phytase was completely released at pH 3-5 by microbial phytase from the aleurone layer. Phytase activity depends on the type of wheat and phytase matrix. The addition of appropriate levels of exogenous enzymes is effective in regulating the gene expression of digestive enzymes and improves the release of trace elements and bone matrix. In this review, based on the available literature, we concluded that the benefits of using WB were much greater than other fiber sources, but more research is needed to compare this valuable fiber source in terms of gut ecology, gene expression, digestibility, behavior, and its interactions with different fat sources.

The poultry gastrointestinal microbiome consists of more than 900 bacterial species and their metabolites; it serves as an indicator of bird health and is influenced by nutrition, medication, and other factors. Dysbiosis is a form of reduced microbial diversity, characterised by the loss of beneficial microbes, the expansion of opportunistic microbes, and the disruption of tight junctions, as well as raised pro-inflammatory cytokines (interleukin-6 and interleukin-17), tumour necrosis factor-α, and Enterobacteriaceae, and decreased short-chain fatty acids. Dysbiosis leads to various disorders, including liver disorders, metabolic disease, cardiovascular disease, and neurological problems. It also impacts several bodily systems, such as the gastrointestinal tract, kidneys, the gut-liver axis (liver disease, hepatocellular carcinoma, autoimmune liver disease, and metabolic-associated fatty liver disease), the gut-lung axis (pneumonia and chronic obstructive pulmonary disease), the gut-microbiota axis (irritable bowel syndrome, inflammatory bowel disease, and constipation or stool hardness), and the gut-islet axis (hypertension, hyperglycaemia, diabetes, and hypercreatinaemia syndrome). Many factors, including medications (antibiotics, anti-tumour, and immunosuppressants), environmental pollutants (heavy metals, pesticides, microplastics, and atmospheric particulates), high levels of nutrients (protein, fat, salt, and sugar), and others (age, disease, habits, and genes), cause and enable gastrointestinal dysbiosis to develop. Nutritional strategies such as the administration of probiotics, prebiotics, antibiotics, or phytogenic feed additives, and the consumption of a high-quality, balanced diet, as well as early detection of gut health malfunction and an emphasis on increasing bird resilience, can reduce the risk of dysbiosis, modify the gut microbial balance, and make microbial eubiosis possible.

The microbiota includes prokaryotes (archaea and bacteria) and eukaryotes. Archaea are single‐celled prokaryotes and essential part of gut microbiome. Researches on archaea in ruminants and humans are more than mono‐gastric. The low abundance of archaea in the gut depends on the method used (metagenomics or meta‐transcriptomic) and age of people or poultry. The lack of complete recognition of archaea is due to their small number and method of identifying them (16S rRNA gene primers). The uses of archaea include analytical kit, reduce oil pollution, archaeosomes or drugs production, vaccines agents, lipid carriers in the pharmaceutical industry and molybdenum extraction in the nuclear industry. The nutritional functions of methanogenic archaea including feed utilization (ruminants) and efficiency, hydrogen reducing (human), fat deposition and enhancement of energy harvesting in mice, CAZymes genes, cecal fermentation, syntrophic potential, carotenoid source and improved transit time and appetite and SCFAs production. Archaea acting as antibiotics (produce archaeocins, sulfolobicins and halocin KPS1) and as probiotics (archaeobiotics) can reduce TMAU (trimethylaminuria) disease, cardiovascular diseases (CVDs), and atherosclerosis, brain abscess, cancer, colorectal cancer, inflammatory bowel disease (IBD), constipation, obesity, food allergies, asthma and anti‐inflammation which can be prevented by using archaea, and other functions include energy homeostasis, heat shock protein (HSP) production and reducing aging.

The production of healthy food is one of the basic requirements and challenges. Research efforts have been introduced in the human's food industry to reduce the microbial resistance and use safe and healthy alternatives with a high durability. However, the conducted work about these issues in the field of livestock animal production have been started since 2015. Inappropriate and extensive use of antibiotics has resulted in the increase of antimicrobial resistance, presence of drug residues in tissues, and destruction of the gut microbiome. Therefore, discovering and developing antibiotic substitutes were urgent demands. Probiotic compounds containing living micro‐organisms are important antibiotic alternative that have been beneficially and extensively used in humans, animals, and poultry. However, some probiotics show some obstacles during production and applications. Accordingly, this review article proposes a comprehensive description of the next‐generation of probiotics including postbiotics, proteobiotics, psychobiotics, immunobiotics and paraprobiotics and their effects on poultry production and human's therapy. These compounds proved great efficiency in terms of restoring gut health, improving performance and general health conditions, modulating the immune response and reducing the pathogenic micro‐organisms. However, more future research work should be carried out regarding this issue.