SYMPOSIUM: THE AVIAN GASTROINTESTINAL TRACT AND DIGESTION1 The Anatomy of the Avian Digestive Tract as Related to Feed Utilization

ABSTRACT The anatomy of the avian GI tract is believed to markedly influence the utilization of feed processed by it. The anterior portion of the tract is adapted for ingestion, storage, and partial digestion of starch and proteins. The structure of the avian intestine is similar to that of other monogastrics except that lacteals are not found. Damage to the intestinal epithelium may decrease nutrient absorption, whereas epithelial replacement may result in improved nutrient utilization. Mitochondrial and other organelle changes are associated with changes in nutrient absorption. The avian intestine has a prominent glycocalyx overlying the microvilli. The avian liver lacks the true lobular structure of the mammalian liver. The hepatocytes are arranged in plates two cell layers thick around the bile caniculi. The avian pancreatic structure contains two main and two smaller lobes containing acinar cells, which secrete digestive enzymes into the the pancreatic ducts, and endocrine cells, which secrete hormones into the general circulation. The structure of the colon is similar to that of the intestine except for poor enervation