Gut peptides are small hormones produced within the gut that are involved in many biological processes including, but not limited to, appetite regulation, mucosal growth, and metabolism regulation. Some peptides, such as cholecystokinin (CCK) and xenin-25 may affect appetite by altering gut motility through cholinergic pathways, but most of the hunger/satiety signals are processed through the brain. Ghrelin is a peptide produced mostly in the gastric stomach or abomasum and increases before a meal. The ghrelin receptor is expressed in neurons in the arcuate nucleus of the hypothalamus and binding leads to the release of neuropeptide Y and agouti-related peptide, thereby stimulating appetite. While ghrelin is thought to serve as a hunger signal in meal fed animals, it may also be involved in the variability of DMI in ad libitum fed animals. Other gut peptides, including peptide YY, oxyntomodulin, and glucagon-like peptide-1 (GLP-1), act as satiety signals and are inhibitory to ghrelin. These peptides stimulate neurons in the arcuate nucleus to release α-melanocyte-stimulating hormone (α-MSH) and cocaine and amphetamine regulated transcript (CART), thereby decreasing appetite. The actions of gut peptides are not limited to appetite regulation. Glucagon-like peptide-2 (GLP-2) is a potent stimulator of intestinal mucosa growth and gut blood flow, and could be important for gut health of livestock. Glucose-dependent insulinotropic polypeptide (GIP) increases insulin secretion and regulates lipid metabolism. Because the complete functions of many gut peptides in livestock species are not known, studying their regulatory roles is critically important in nutritional physiology and animal health.