Chapter 4 - Phytase in animal feed

Abstract

Phytic acid is a compound found in plants that stores phosphorus (P) in a highly stable form and also binds with various nutrients including minerals, proteins, starches, and lipids. Many plant-based ingredients commonly added in the diets of terrestrial and aquatic animal feeds are high in phytic acid. For nonruminant animals, phytic acid is largely indigestible and therefore can reduce nutrient utilization leading to reduced growth and bone mineralization as well as excessive phytic-P discharge to the environment. Some secondary effects to the host animal can include suppressing appetite, digestive enzymes, or irritating the gut. The enzyme phytase degrades phytic acid and can be used as an effective pretreatment to ingredients or directly included as a safe supplement in animal feeds to reduce these harmful effects. Generally, phytase greatly improves mineral digestibility in animals, but its effects as a growth promoter are highly variable. The efficiency of this enzyme depends on pH, presence of P and calcium (Ca), phytase type/level as well as interactions with other ingredients or nonphytase enzymes. To optimize phytase activity, diets should be deficient in P and Ca, while dietary acidifiers such as some organic acids may exert synergistic effects to digestibility and/or growth. Moreover, nonphytase enzymes, particularly carbohydrate-degrading enzymes, may allow more sites for phytase activity in plant-based ingredients. These interactions are receiving increasing attention, with indications that the gastrointestinal health of animals can also be improved. Indeed, rather than phytase being viewed as a means to substitute for additional P supplementations, and thus being more environmentally friendly, the inclusion of phytase with other natural supplements has the potential to act as a prophylactic to disease.