Comparison of phytase sources
Several phytase sources are commercially available for use in swine diets. Because of differences in phytase characteristics and variation in recommended levels for similar phosphorus release among products, there is an interest to be able to effectively compare phytase sources (Jones et al., 2010). An approach for comparing different phytase sources is to compare the phytase activity needed to reach a particular available phosphorus or standardized total tract digestible phosphorus release value. This allows for products to be compared on the same level of activity to determine replacement rates for each phytase source (Gonçalves et al., 2016). Table 1 presents the release values for comparison of some of the current commercial phytase sources using this approach. A phytase calculator has also been developed for these commercial phytase sources (KSU Phytase Calculator).
Moreover, analytical techniques used to determine phosphorus release values are variable among commercial phytase manufacturers (Jacela et al., 2010). Because of this, the amount of phosphorus released per unit of phytase differ between phytase products. The standard method is the AOAC assay (AOAC, 2000), but some phytase suppliers modify this method according to different phytase characteristics.