The application of phytases in feed is common practice in monogastric nutrition. To prevent phosphorus (P) deficiency, phytases need to be well formulated in feed.
Phytases are used to liberate P which is bound as phytate in raw materials. This reduces feed costs as less inorganic P needs to be added to the feed to provide enough available P (aP). However, phytases need to be well formulated in feed, as too low aP levels will lead to reduced bone growth and lower animal performance in general.
Causes of P deficiency
There are two major reasons for P deficiency when a phytase is used in feed:
- Low heat stability of the phytase during pelleting
- An overestimation of its P matrix values
Need for a heat-stable phytase
To avoid the breakdown of the added phytase during pelleting, the phytase must have high thermostability. An overview of the average recovery of the novel intrinsically heat-stable phytase OptiPhos® Plus, which was determined in over ten pelleting studies, is shown in Figure 1. It is evident that OptiPhos® Plus has intrinsic heat stability at 85oC (recovery > 80%) when applied in granular form (G). When a coated version (CT) is used, stability up to 95oC is observed.
Need for reliable P matrix values
The P matrix values provide information to a nutritionist about how much inorganic P can be replaced by incorporating phytase in the feed. To provide reliable matrix values, multiple trials need to be conducted. These can be assessed either by carrying out regular digestibility trials, or bone ash trials, in which the response to P release from phytate is measured by adding the phytase at different doses to a P-deficient feed. For OptiPhos® Plus, a value of 1.55 g aP was determined at 500 FTU/kg in broilers, based on all trials conducted (12 in total). However, only considering the six trials which showed the best response for P release from phytate, an aP value of 1.65 g/kg was determined. Similarly, based on 11 trials in pigs, an aP value of 1.40 g per kg feed was determined, while an aP value of 1.56 g/kg was calculated when only the three trials with the best response were considered.
In both cases, the differently calculated aP values result in feed cost savings of €0.32/tonne (€3.54/tonne for the best trials minus €3.22/tonne for the average of all trials) for broilers, and of €0.35/tonne (€3.55/tonne for the best trials minus €3.00/tonne for the average of all trials) for pigs. This difference might prompt phytase suppliers to use only the best trials for establishing the P matrix values, so that they can be the best buy. However, this increases the risk for the nutritionist that P deficiency issues might occur, leading to lower animal performance. In that case, the financial loss will surely be much higher than the saving on the formulation cost. It is therefore better to use the average P matrix values of all conducted trials, and not just to rely on the best ones.
Excellent recovery of phytase in pelleted feed needs to be guaranteed, combined with reliable and safe P matrix values originating from multiple trials in order to avoid any risk of P deficiency and thus financial losses at the farm level.