Enzymes are natural proteins that break down large feed components into more minor simple compounds. These simple compounds are then absorbed to be used by the animal for maintenance and production. Without the enzyme's digestion process, the nutrients can't be absorbed by the animal.
First, they need a suitable substrate. Thus, a protease cannot break down carbohydrates, nor can a phytase work on a protein. So, there must be a match between each enzyme and its substrate. The enzyme recognizes and attaches itself to the substrate in a mechanism resembling a key-and-lock analogy.
Second, they need the proper environment in terms of acidity or alkalinity. For example, enzymes secreted in the stomach work best under low pH (acidic) as this is the natural environment of the stomach. In contrast, enzymes secreted in the small intestine work best in a higher pH environment for the same reason.
Commercial enzymes (exogenous) are used to enhance the natural process of digestion. Examples include amylase (starch) and protease (protein). Other enzymes provide for the digestion of substrates that the animal does not digest. This includes phytase (phytate phosphorus) and xylanase-glucanase (fibre components).
Exogenous enzymes are also natural proteins produced by controlled microbial fermentation and work under the same principles as endogenous enzymes. Like their endogenous counterparts, they too require the proper substrate and correct pH conditions to exert their full effect. In addition, there are a few other requirements for exogenous enzymes: they must be stable under diverse feed processing and storage conditions, safe for human operators, and of course, their use must improve profitability for the animal producer! Today, we can easily expect a 10% improvement in phosphorus digestibility by a modern phytase. Likewise, a glucanase or xylanase enzyme can improve metabolizable energy in feed by about 50 kcal/kg or even more (up to 150 kcal/kg is not unreasonable for low-quality cereals). Finally, a protease improves protein digestibility by around 2-5%, depending on the ingredients used.
In the animal industry, where profit margins are thin, such improvements as those conferred by exogenous enzymes are indeed substantial.
In conclusion, enzymes are natural, safe, and essential for the animals. Supplementation in feed enhances digestion and reduces the amount of feed being excreted. This, in turn, improves animal performance and profitability and reduces environmental pollution.