Digestibility of food. Digestibility refers to how much of the food is actually absorbed by the bird's system. The more food that is actually metabolized, the higher the digestibility. During feeding trials, the birds' feces are collected and analyzed to determine the undigested residues of the food eaten. High digestibility indicates that the nutrients within a given food are readily available to be used by the animal.
Consideration is given, too, to the type of bird and the normal digestive processes for that bird.
Quality before processing. Understanding the definition of an ingredient is not enough. The short description doesn't tell us exactly how good that ingredient is. Many grains grown in poor soil will lack needed vitamins and minerals, and unfortunately, this happens quite often in the United States. Grains and Vegetables can also be polluted with pesticides of various kinds and fertilizer residues, herbicides and anti-fungal sprays.