Profitability and sustainability of animal production systems depend on health status and productivity of animals and birds, both of the later directly influenced by gastrointestinal or gut health. Gut health influences utilization of feed and development of immunity in animals and birds. Gut health is affected by many factors, amongst which role of intestinal epithelial cells, microbiota of the gut and nutritional management are the main factors influencing the health and immunity, and hence the productivity and optimal performance of animals and birds.