This review explains how the trillions of microorganisms living in animal intestines are crucial for health and digestion. When these microbial communities become imbalanced, animals develop diarrhea, which is a major problem in farming causing economic losses and animal suffering. The review shows that adding beneficial bacteria (probiotics) and their food sources (prebiotics) to animal diets can restore balance and prevent diarrhea, offering practical solutions to reduce the need for antibiotics.