At the same time, the sustainability of animal production is improved as P excretion in the environment is reduced. However, phytases need to be well formulated in feed as too low a P level will lead to reduced bone growth and animal performance in general. This is of particular concern in sow and piglet nutrition, as bad bone formation will lead to impaired mobility.
Avoiding P deficiency
Two factors may contribute to P deficiency, even when the phytase is dosed correctly in the mash feed. First of all, the stability of the phytase: in particular its heat stability when dosed in feed for pelleting. Secondly, the phytase needs to provide reliable P matrix values to avoid overestimation of its potential to release P from phytate.
Thermostability of the phytase
Due to their proteinous nature, phytases can lose activity during the pelleting process. This results in feed with a phytase activity which does not meet the feed specificiations on digestible P, and thereby will yield less efficient animal performance. Therefore it is required that the phytase demonstrates a high thermostability to at least 85oC, which means that it must show more than 80% recovery of the initial activity after the pelleting process.
A summary of three pelleting studies carried out at the Ghent University, Belgium showed that a newly launched intrinsic heat stable phytase (OptiPhos® Plus G) yields recoveries that were 88.5% at 85oC and were even close to 80% at 90oC (Figure 1).
Reliable P matrix values for the nutritionist's peace of mind
The capacity of a phytase to replace inorganic phosphates in the feed is summarised through P matrix values for available P and/or digestible P. This can be assessed either by regular digestibility trials, or by bone ash trials in which the response on P release from phytate is measured when adding the phytase at different doses to a P-deficient feed. To provide reliable matrix values, multiple trials need to be conducted. For OptiPhos® Plus for instance, 11 pig trials have already been conducted giving an average dig. P improvement for different inclusion levels (Figure 2).
In addition to the average results of these 11 trials, Figure 2 also shows the average of the three trials giving the best response of OptiPhos® Plus. From these response curves, it can be deducted that an OptiPhos® Plus dose of 500 FTU/kg provides a dig. P matrix value of 1.12g/kg dig. P when considering all trials. A value of 1.25g/kg can be estimated when only the best three trials are considered. Assuming the price of monocalciumphosphate at €0.45/kg containing 18.3% dig. P, a cost saving per tonne of feed of €2.75 and €3.07/tonne could be estimated when considering the average response of all 11 trials, or only of the best three trials, respectively.
The price difference (€0.33/tonne) can be a trigger for a phytase supplier to promote the P matrix values of only these three trials in order to fight competition. However, this increases the risk for a nutritionist that, in some cases, P deficiency issues can occur. In these cases, the financial losses will surely be much higher than the saving on the formulation cost. Therefore, it is advisable to always work with the average P matrix values of all conducted trials, and not just to rely on the best ones.
Conclusion
It can be concluded that in order to avoid P deficiency in pigs, an excellent recovery of phytase in pelleted feed needs to be guaranteed. In addition, reliable P matrix values need to be provided from multiple trials. It needs to be avoided that P matrix values, calculated from only the best trials, are used during formulations, as this can cause P deficiency at farm level.
