The efficacy of phytase varies with phytase characteristics, which are determined based on phytase origin (bacterial or fungal phytase), phytase generation (first or new generation), and site of action of phytase on phytate (3- or 6-phytase, referring to the initial carbon site of hydrolysis on phytate). The most important characteristics influencing phytase efficacy include activity in the upper digestive tract, affinity to phytate, and resistance to degradation.
Characteristics influencing phytase efficacy
- Activity in the upper digestive tract: The degradation of phytate in the upper part of the digestive tract (stomach and upper small intestine) is essential to improve phosphorus availability and eliminate the antinutritional effects of phytate (Dersjant-Li et al., 2014). The optimal pH range of phytase provides an indication of phytase activity in the upper part of the digestive tract. The pH in the pigs’ empty stomach is normally 2.0 to 2.5 and gradually increases to 3.5 to 4.0 with feed, whereas the pH in the pig’s upper small intestine is around 4.0 to 6.0 (Pagano et al., 2007). The optimal pH for phytase activity typically varies over a range of 2.5 to 5.5.
- Affinity to phytate: The most effective phytases have great affinity to phytate and are able to target phytate at low concentration and from many feedstuff sources (Dersjant-Li et al., 2014).
- Resistance to degradation: As phytase is a protein that can be degraded by enzymes in the digestive tract, the most effective phytases are resistant to degradation by enzymes in the digestive tract (Dersjant-Li et al., 2014).
Dietary factors influencing phytase efficacy
Beyond the phytase characteristics, several factors influence the efficacy of phytase, including the amount of phytate in the diet, the amount of phytase added to the diet, and diet formulation. Although it is not clear to which extent diet formulation affects phytase efficacy, it is important to understand the dietary factors that influence the activity of phytase.
- Feedstuffs: There is considerable variation in the susceptibility of phytate to phytase depending on feedstuff. Also, the amount of intrinsic phytase varies with feedstuff, with wheat containing more intrinsic phytase than corn, for example (Selle and Ravindran, 2008).
- Ratio of phytase to phytate: The ideal ratio of phytase to phytate allows for maximum release of phosphorus from phytate. However, in most of the cases, either phytase or phytate levels are limiting. When phytase is the limiting factor, the release of phosphorus improves with addition of more phytase. When phytate is the limiting factor, the release of phosphorus occurs until all phytate is depleted by phytase but does not improve with further addition of phytase (Cowieson et al., 2016).
- Inorganic sources of calcium and phosphorus: The use of high concentrations of inorganic sources of calcium and phosphorus interfere in phytase efficacy. Sources such as limestone and monocalcium phosphate have the potential to increase gut pH, which affects phytase activity and reduces phytate solubility (Dersjant-Li et al., 2014).
- Calcium level and Ca:P ratio: Diets formulated with high calcium levels and wide calcium:phosphorus ratios will lower phytase efficacy. Calcium forms a complex with phytate which reduces phytate susceptibility to phytase activity (Selle et al., 2009).
- Pharmacological levels of zinc: Diets formulated with pharmacological levels of zinc have lower phytase efficacy. Similar to calcium, zinc forms a complex with phytate which reduces phytate susceptibility to phytase activity (Selle and Ravindran, 2008).