High phytase dosing optimises animal performance

In recent years, increasing prices of inorganic phosphorus (P) sources has led to higher inclusion levels of phytase in feeds, rising from 500 to 1000 FTU/kg and even 2000 FTU/kg. Although the recent drop in prices has tempered this tendency, it is still economically viable to consider higher dosing (and superdosing) of phytase as it optimises animal performance.

The antinutritional effects of phytate

Phytate-phosphorus has an anti-nutritional action. Due to its negative charge, it binds to minerals such as calcium, zinc and copper, but also amino acids, making them less available for the animal. In addition, phytate is known to increase the loss of endogenous protein, which needs to be replaced at the expense of protein normally available to the animal. By superdosing phytase, more phytate is broken down which reduces these effects, ensuring that nutrients stay available to the animal, enhancing its performance. For instance, in large broiler studies it has been shown that increasing the inclusion level of the heat stable phytase OptiPhos Plus improves protein digestibility (Table 1).

Realistic expectations

While some phytases currently on the market claim 4-5% improvements in amino acid digestibility due to superdosing, these claims mostly come from studies carried out with feed formulations which do not represent commercially viable feed formulations. Or they come from trials where excess protein is present in the feed, making it easy to prove the claimed amino acid matrix values for a phytase – you are simply removing the excess protein, not contributing to performance. The golden rule regarding expectations of improvements in protein digestibility from superdosing a phytase in commercial feeds is as follows:

1. Up to 1% improvement: sure;
2. Up to 2% improvement: maybe
3. Above 2% improvement: do not count on it.

This also applies to improvements in performance: an improvement of 1 to 2 % in growth and feed conversion is a realistic expectation of superdosing in commercially viable feed formulations.

The economics of superdosing: it pays for itself

We can estimate how much performance needs to increase to be economically beneficial when shifting from a dose of 500 FTU/kg to 2000 FTU/kg, assuming there is no feed price reduction due to reformulation (so the phytase addition is an extra cost). For broilers, an extra end weight of 7.5 g or an improvement in feed conversion of 0.008 (or a combination) is needed for a financial break even. In the case of fattening pigs, a 3000 g higher end weight or a 0.015 improvement in feed conversion is required. This means that a very small improvement in performance is already enough to break even, so any higher improvement of performance will deliver a financial return on investment.