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 3 presents the aP and STTD P release values for comparison of some of the current commercial phytase sources. To provide consistent information to swine producers, data has been summarized and a calculator (KSU Phytase Calculator) has been developed to provide recommendations for release of phosphorous in swine diets.
Data used in this tool has been provided by phytase suppliers and all release values are based on bone mineralization measures including bone ash, dual energy x-ray absorptiometry (DEXA) scans, and/or bone phosphorous analysis when available in the data.
It is recognized that phytase provides growth benefits beyond bone mineralization. However, the goal of this tool is to provide release estimates for phytase sources based on estimates of bone mineralization.
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.
An important concept with this calculator is that 100% of the phytate P is not digestible even when adequate phytase is available. Thus, the expected release of phosphorous is dependent upon the amount of phytate P within the diet. The exact proportion of phytate P that can be release and become available to the pig is not fully understood. To incorporate this concept with the best information currently available, the calculator uses a default of 70% to provide an estimate of the potential amount of the dietary phytate P that can be released if adequate phytase is available.
The phytase level used within all calculations was based on assayed concentration of phytase source, and phytase units are reported using manufacturer assay.