Poultry Biology - Raising Poultry - page 53

The air sacs and lungs also help with thermoregulation. Heat and moisture are both
removed from the body through respiration. See page 59 , at the end of this chapter, for
a more detailed discussion of body temperature regulation.
The Digestive System
Poultry are all omnivores and their digestive system is characteristic of that feeding
habit. They do not have lips, a soft palate, or teeth. Their mandibles (jaws) are referred
to as a beak. The upper mandible is attached to the skull and the lower is hinged. The
hard palate (the roof of the mouth) is divided by a long narrow slit that allows airflow
to the nasal passages. This slit in the roof of the mouth makes it impossible for the birds
to create a vacuum to draw water into the mouth. The bird must raise its head every time
it takes a drink, using gravity to move the water down.
The tongue is pointed at the front and brush-like at the back to help push food down
the esophagus (gullet). Saliva with the enzyme amylase is secreted by the glands of the
mouth to help lubricate the food and aid in its passage down the esophagus. At the base
of the esophagus is the crop , which serves as a storage place for food before it enters the
proventriculus, which is the true stomach. In the proventriculus, hydrochloric acid and
digestive enzymes begin the digestive process.
Food then passes into the ventriculus, more commonly known as the gizzard, where
it is ground into smaller particles. Adding tiny pieces of rock called grit to the diet aids
in the grinding process and shortens the amount of time food spends in the gizzard.
Feeding a laying crumble or pellet will most likely mean little need for grit as the feed
is already ground up and thus spends very little time in the gizzard. If the feed ration is
whole scratch grains, the birds need grit and the feed will spend more time digesting in
the gizzard.
THE DIGESTIVE SYSTEM