Enzymes are biological catalysts that accelerate chemical reactions. They are proteins, with complex structures that allow them to remain stable during the high temperatures necessary for feed manufacture, and while moving through the animal's gastrointestinal tract. One of the most important characteristics of the enzyme is its ability to break down specific substrates in precise reaction sites. The exact enzymes used in the enrichment of feedstuffs are purposefully selected to target distinct substrates used in that feed. Enzymes will only react under certain conditions. The moisture content, quantity of enzymes used, temperature, and pH levels during use must meet the enzymes' specific reactive requirements for them to function effectively.