Antibiotics in Animal Feeds: Are There Viable Alternatives?

The proglucagon (PG) gene is expressed in the gastrointestinal tract (GI) and brain in several animal species. The PG gene is differentially translated in the GI tract by specific endocrine cells to produce glucagon in the pancreas and glucagon-like peptides 1 and 2 (GLP-1/GLP-2), glicentin, and oxyntomodulin in the intestine. These PG-derived peptides have diverse functions involving insulin secretion, motility, and tissue growth within the GI tract, but also have systemic actions on glucose homeostasis and appetite regulation. There is considerable interest in the therapeutic potential of GLP-1 and GLP-2 in respective treatment of type-2 diabetes and intestinal dysfunction, including shortbowel syndrome and inflammatory bowel disease. GLP-1 and GLP-2 are co-secreted from the gut in response to enteral nutrition, particularly fat and carbohydrate, but are suppressed by total parenteral nutrition. GLP-1 and GLP-2 secretion are also stimulated by short-chain fatty acids that are produced by colonic fermentation of malabsorbed carbohydrate and dietary fiber. GLP-1 is a key incretin hormone that increases insulin secretion, islet neogenesis, b-cell proliferation. GLP-2 is a potent intestinotrophic hormone that increases intestinal mucosal cell proliferation, blood flow and suppresses apoptosis and inflammation. The GLP-1/2 receptors are G-protein-coupled membrane proteins that signal via intracellular cAMP release. The GLP-1/2 receptors are expressed in the brain and GI tract; however, the cellular localization is poorly understood. There is limited information on the biological function of GLP1/2 in the growth and development of domestic animals. However, these hormones may be possible therapeutic targets for modulation of feed intake and intestinal dysfunction in production animals.