Effect of phytase on nutrient digestibility, mineral utilization and performance in growing pigs

Two experiments were conducted to investigate the effect of microbial phytase addition to a low total phosphorus (tP) diet on the apparent faecal digestibility of nutrients and the N, P, Ca, Mg, Cu and Zn balance, and on the growth performance and tissue mineral concentration in growing pigs. Three experimental diets were used; the control diet (C) with 5.8 g tP/kg without phytase, and two low tP diets (4.5 g tP/kg) without phytase (LP−), or with 500 FTU/kg of microbial phytase (LP+). All diets were formulated to be isoenergetic (13.59 MJ ME/kg) and to have a similar digestible lysine:ME ratio. In experiment 1 (digestibility study), pigs were housed individually in metabolism cages and each diet was rotated three times according to 3×3 Latin square designs. Phytase supplementation resulted in higher P, Ca, Mg and Cu digestibilities and P and Cu retention, which could result in a decrease in the excretion to the environment of 39% and 33% for P and Cu, respectively. In Experiment 2 (growth performance and tissue mineral concentration study), phytase supplementation reversed the lower average daily feed intake and final body weight produced by the decrease of tP in growing pig diets. Neither alkaline phosphatase activity nor plasma Ca concentration was affected (P>0.05) by dietary treatment, but plasma inorganic phosphorus was higher in pigs fed the LP+ diet than in those fed the LP− diet. In addition, bone ash weight, peak breaking strength and the concentration of most of the minerals analysed on metacarpal bone were not affected by phytase supplementation, except for an increase in Mg concentration. No effects of phytase addition were observed on mineral concentration, except for increased Zn concentration in the pancreas of pigs fed LP+. In conclusion, under our study conditions, phytase supplementation improved the growth performance and digestibility of most minerals studied. P and Cu were the most likely minerals to be affected by the addition of phytase, increasing their retention, which represented a decrease in the excretion into the environment from pig manure by 39% and 33% for P and Cu, respectively. However, the mineral concentration in heart, liver and muscle were not affected by diet, meaning that it is inadvisable to take one organ as target to study the effects of phytase supplementation.