Phytase in non-ruminant animal nutrition: a critical review on phytase activities in the gastrointestinal tract and influencing factors

Abstract

This review focuses on phytase functionality in the digestive tract of farmed non-ruminant animals and the factors influencing in vivo phytase enzyme activity. In pigs, feed phytase is mainly active in the stomach and upper part of the small intestine, and added phytase activity is not recovered in the ileum. In poultry, feed phytase activities are mainly found in the upper part of the digestive tract, including the crop, proventriculus and gizzard. For fish with a stomach, phytase activities are mainly in the stomach. Many factors can influence the efficiency of feed phytase in the gastrointestinal tract, and they can be divided into three main groups: (i) phytase related; (ii) dietary related and (iii) animal related. Phytase-related factors include type of phytase (e.g. 3- or 6-phytase; bacterial or fungal phytase origin), the pH optimum and the resistance of phytase to endogenous protease. Dietary-related factors are mainly associated with dietary phytate content, feed ingredient composition and feed processing, and total P, Ca and Na content. Animal-related factors include species, gender and age of animals. To eliminate the antinutritional effects of phytate (IP6), it needs to be hydrolyzed as quickly as possible by phytase in the upper part of the digestive tract. A phytase that works over a wide range of pH values and is active in the stomach and upper intestine (along with several other characteristics and in addition to being refractory to endogenous enzymes) would be ideal.

Keywords: digestive tract; fish; phytase activity; pigs; poultry.

Figure 1

Structure of phytic acid (myo-inositol, 1,2,3,4,5,6-hexakisphosphate (IP6, IUPAC).

Figure 2

The aggregation of soy protein by myo-inositol phosphate esters (IP_1–6) and IP₅ positional isomers. Each data point is the average of four measurements with SD. Source: Yu et al.

Figure 3

Relative activity of different commercial phytases. Left-hand figure compares three commercial phytases (A. niger, E. coli and P. lycii) when using the activity at pH 5.5 as 100%. Source: Kumar et al. Right-hand figure compares two commercial phytases (E. coli and P. lycii); the maximum phytase activity recorded was considered as 100%. Source: Morales et al.

Figure 4

Residual phytase activity of E. coli and P. lycii phytase after incubation with pepsin or a gastric crude extract from trout stomach for up to 4 h. The incubation was performed by adding 1 FTU phytase to a protease solution with 5000 U pepsin or gastric crude extract from fish at pH 2.0 and 16 °C. Different letters indicate significant difference (P <0.05). Adapted from Morales et al.

Figure 5

Phytase activity of digesta from various segments of the gut of pigs fed a basal diet or diets supplemented with 500 and 2000 FTU phytase kg⁻¹. A–C: for each segment, means not sharing a common letter differ (P <0.05). Graph adapted from Pagano et al.

Figure 6

Effect of microbial phytase inclusion on dephosphorylation of phytate during preparation of cold pelleted diet.

Figure 7

Illustration of factors influencing in vivo phytase activity and factors influencing phytase efficiency measurement.