With the advancement of microbiome research, the requirement to consider the intestinal microbiome as the "last organ" of an animal emerged. Through the production of metabolites and/or the stimulation of the host's hormone and neurotransmitter synthesis, the gut microbiota can potentially affect the host's eating behavior both long and short-term. Based on current evidence, the major mediators appear to be short-chain fatty acids (SCFA), peptide hormones such as peptide YY (PYY) and glucagon-like peptide-1 (GLP-1), as well as the amino acid tryptophan with the associated neurotransmitter serotonin, dopamine and γ-Aminobutyrate (GABA). The influence appears to extend into central neuronal networks and the expression of taste receptors. An interconnection of metabolic processes with mechanisms of taste sensation suggests that the gut microbiota may even influence the sensations of their host. This review provides a summary of the current status of microbiome research in farm animals with respect to general appetite regulation and microbiota-related observations made on the influence on feed intake. This is briefly contrasted with the existing findings from research with rodent models in order to identify future research needs. Increasing our understanding of appetite regulation could improve the management of feed intake, feed frustration and anorexia related to unhealthy conditions in farm animals.
Keywords: appetite; eating behavior; farm animals; feed intake; intestine; microbiome; neurotransmitters; physiology; taste reception.