Abstract: The gastrointestinal tract is the largest microecosystem in animals, where complex microbial communities constitute the animal’s intestinal microbial barrier. 5-Hydroxytryptamine (5-HT), commonly known as serotonin, is a neurotransmitter in animals, with more than 90% produced by the intestine, which exhibits various biological functions including the regulation of intestinal peristalsis, secretion processes, immune responses, and maintenance of intestinal barrier integrity.As a pivotal signaling molecule in the gut-brain axis, 5-HT can transmit information through the nervous, endocrine, and immune systems; thus playing a vital role in maintaining neural and intestinal homeostasis while modulating disease states. Currently, research on 5-HT mainly focuses on fields such as biology, medicine, ethology, and psychology, however, studies pertaining to its implications in livestock and poultry remain scarce. This paper systematically reviews the regulatory mechanisms of 5-HT in neurological abnormal behaviors and intestinal diseases of rodents, livestock, and poultry. It also discusses the regulation of intestinal 5-HT synthesis and microbial balance by adding tryptophan precursors such as rumen-protected 5-hydroxytryptophan (5-HTP), probiotics, or plant extracts (such as Astragalus polysaccharide, natural capsaicin) to alleviate intestinal disorders such as post-weaning diarrhea in piglets and necrotic enteritis in broilers. Under stress scenarios such as heat stress or transport stress, enhancing 5-HT levels via probiotic supplementation or regulating intestinal 5-HT receptor gene expression through colostrum feeding can mitigate stress-induced behavioral abnormalities and immune dysfunctions. These findings aim to provide theoretical support for practical applications in animal husbandry.

Key words: 5-HT, gut microbiota, gut-brain axis, neurobehavioral disorders, intestinal inflammation