The Effects of Super-dosing Phytase in the Growing Pig

Microbial phytase enzymes are commonly added to monogastric diets at 500 FTU/kg feed (as fed) to improve phytate phosphorus (P) bioavailability and reduce P excretion. The use of super-doses of phytase (>1,500 FTU/kg as fed) is currently generating much interest, as recent studies have demonstrated that such high doses can improve the growth performance of monogastrics. However, the underlying mechanism for this response remains unclear. At present, there is a dearth of information available on the effects of super-dosing in the pig. Therefore, this research set out to determine the effects of super-dosing phytase on the growing pig, with a view to shedding light on underlying mechanism, particularly in relation to the possible involvement of myo-inositol (MYO). Through three separate feeding trials, this work found that super-dosing phytase improved the growth performance of weaner pigs, but had no influence on the growth performance of grower or finisher pigs. Ileal digesta were collected and analysed for inositol phosphate content by HPIC. Standard doses of phytase resulted in a small accumulation of InsP4 and InsP3 phytate esters in the ileal digesta of weaner and finisher pigs. This build-up was effectively diminished when supplemented with a phytase super-dose, resulting in more complete phytate degradation. High doses of phytase consistently increased circulating levels of MYO in both the portal and peripheral blood in weaner, grower and finisher pigs. Super-doses of phytase were consistently associated with increases in Ca, P and Mg bioavailability across all stages of production. Moreover, there were also indications of improved trace mineral (Zn, Cu, Fe, Mn) digestibility; however, this effect was less consistent. From this thesis it can be concluded that super-doses of phytase are associated with an increase in phytate hydrolysis and a concomitant increase MYO absorption. However, these effects do not always translate into improved pig performance. Further research is needed to elucidate the factors responsible for the inconsistencies observed.