There is a growing body of evidence that shows that dosing above the traditional industry standard of 500 FTU/kg, can have a beneficial effect on pig performance, depending on the type of phytase used. Two recent studies13 evaluated the effect of a Buttiauxella phytase at 1000 FTU/kg on digestibility of calcium and phosphorus in weaner pigs (9-22 kg bodyweight). Based on bone ash and body weight gain data, the studies established that this phytase successfully replaced 0.2% available phosphorus in weaning piglet diets. A further study14 evaluated the effect of varying doses of Buttiauxella phytase on ileal tract nutrient and total tract digestibility in growing pigs fed a corn-soy based diet. Digestibility of calcium and phosphorus responded with increasing phytase dosing, with improvements of up to 33.8% in calcium uptake and 124.3% in phosphorus for diets supplemented with 2000 FTU/kg phytase. As phytase is increasingly used with other additives, it is also important for producers to have evidence not only of how these varying elements of the diet interact but also how this impacts phytase dosing. Take, for example, the addition of zinc oxide; studies show that zinc can bind to phytate, rendering it less accessible to phytase15 and that the high zinc levels used in many post-weaning diets can compromise the efficacy of phytase at 'conventional' doses e.g. 500 FTU/kg feed16. Recent trials17 have shown that the use of phytase at 1000 FTU/kg feed (and higher) gave good growth and feed conversion responses in phosphorus-adequate piglet diets containing 2500 mg/kg of zinc oxide and with a phytate P level of 0.28%.The best performance in this series of trials was achieved with a dose of 2000 FTU/kg feed.