Chapter 18 - Carbohydrate Metabolism

Abstract

Our understanding of avian carbohydrate metabolism most frequently comes from studies on chicken, though they have the disadvantages of domestication and falling outside the major evolutionary groupings of birds, like other that galliform birds. Overall, carbohydrate metabolism in birds is very similar to that in mammals. Small intestine is the major site for the digestion of starch and the absorption of glucose and other monsaccharides. Glucose can be used for energy via glycolysis, the citric acid cycle, or the pentose pathway. Some tissues that are incapable of using fatty acids use only glucose. Glucose can be stored as the polysaccharide glycogen in the liver, muscles, and other tissues or used as a substrate to produce fatty acids (lipogenesis), which in turn are stored as triglycerides in adipose tissue. Glucose can be synthesized from lactate, amino acids, and other gluconeogenic precursors in the liver and the kidneys. The differences between avian and mammalian carbohydrate metabolism include very high circulating concentrations of glucose in birds, absence of one of the glucose transporters, and major nutrients available to the developing embryo being fats and proteins, together with the liver being the site of lipogenesis. Circulating concentrations of glucose exhibit marked differences across avian species during development and with external environment. Moreover, they are under tight control. This chapter will discuss avian carbohydrate digestion, metabolism, and circulating glucose together with their control.