The term poultry refers to domesticated birds used for the production of meat and eggs.

Chickens are the most common poultry worldwide, followed by turkeys in the United States and ducks and geese elsewhere. Because poultry can be maintained in a relatively small space and are extremely efficient in converting plant protein to animal protein, they are a sig­nificant source of animal protein in developing countries, as well as the rest of the world.

The domestic chicken (Gallus gallus or Gallus domesticus) and turkey (Meleagris gallopavo) are in the order Galliformes, whereas domestic ducks (Anas platyrhynchos and Cairina mos- chata) and geese (Anser anser and Anser cygnoi- des) are Anseriformes. All are in the superorder, Carinatae. In this chapter, the term gallina­ceous will refer to chickens and turkeys, and fowl will refer to all domesticated birds. The emu, rhea, and ostrich are in a separate super­order of flightless birds, Ratitae. Table 30-1 lists terms commonly used for poultry of different genders, ages, and reproductive status.

Studies of domestic chickens are the basis for most of the avian physiology in this chapter,

and much of this information (e.g., urinary excretion of uric acid, basics of respiratory function) could be applied to all birds. However, turkeys and chickens raised by producers in the United states have been derived by intense genetic selection for egg andIor meat produc­tion, and these domesticated birds have some anatomical and physiological characteristics that are quite different from their wild ances­tors.