The tremendous amounts of feed handled by commercial poultry breeds require an optimally functioning digestive tract. Functionality of the different segments of the digestive tract may be affected by diet and feeding systems, however. Retention time, moisture content, and pH of contents in the crop are, to a large extent, determined by feeding systems, where intermittent feeding is necessary for a stimulation of crop use. Retention time and pH of the gizzard contents are similarly affected by access to structural components, such as whole cereals or coarse fibers. These materials will stimulate normal development of the gizzard, increase retention time, and decrease pH. less is known about characteristics of an optimally functioning small intestine, but stimulation of gizzard development will possibly improve functionality of the small intestine through a better feed flow regulation. Functionality of the digestive tract will possibly have a large effect on response to dietary manipulations (e.g., enzyme and pre- or probiotics addition), and therefore needs to be taken into consideration in experimental design and results interpretation.
