Gut dysbiosis: Nutritional causes and risk prevention in poultry, with reference to other animals

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.