There are many different enzymes added to pig diets around the world, so the maximum or indeed optimum levels would depend on many factors. These may include things such as the enzyme (common in Europe are phytases and xylanases to name but a few), the source (e.g. a 3-phytase or a 6-phytase), the formulation (e.g. thermo-stable and/or coated) and the class of pig (sow, grower, piglet). A good place to look for the maximum level may be on the EU (or FDA) product registration documents, as companies are often required to test large doses for safety reasons and report their efficacy.  

according to its age and diet composition