Effects of super-dosing phytase and inositol on growth performance and blood metabolites of weaned pigs housed under commercial conditions1.

A total of 2,156 weaned pigs (6.75 ± 0.11 kg BW) were used in a 42-d study to evaluate whether improvements in growth performance associated with super-dosing phytase can be explained by the complete dephosphorylation of phytate and liberation of inositol. Two phytase doses (0 and 2,500 FTU/kg) and 3 inositol concentrations (0%, 0.15%, and 0.30%) were combined to create 6 dietary treatments in a 2 × 3 factorial arrangement. Pigs were fed a 3-phase feeding program, with periods being 10, 10, and 22 d, respectively. Blood samples were collected on days 0, 21, and 42 from a subset of 48 pigs to analyze mineral and myo-inositol concentrations. During Phase 1, super-dosing phytase tended to improve ADG compared with pigs fed diets without phytase (P = 0.09). Increasing concentrations of inositol improved the efficiency of gain in pigs fed diets without phytase (1,022.1, 1,040.9, and 1,089.2 g/kg), but not diets with phytase (1,102.2, 1,087.2, and 1,076.2 g/kg), and this improvement was equivalent to that observed with super-dosing phytase in the absence of inositol (interaction, P = 0.015). During Phase 2, super-dosing phytase improved ADG (P = 0.001), resulting in heavier BW (P = 0.007). During Phase 3 and overall, inositol supplementation increased ADG and ADFI in a quadratic manner (P < 0.10), with the highest ADG and ADFI observed for pigs fed 0.15% of inositol. Super-dosing phytase increased serum Zn on day 21, but not on day 42 (interaction, P = 0.008), increased serum Cu (P = 0.01), but decreased serum Fe (P = 0.02). Plasma myo-inositol increased linearly from 66.9 to 97.1 and 113.2 nmol/mL with increasing inositol (P < 0.001). When plasma myo-inositol was analyzed within the subgroup of pigs fed diets without added inositol, super-dosing phytase increased plasma myo-inositol from 57.81 to 76.05 nmol/mL (0 and 2,500 FTU/kg, respectively; P = 0.05). Results demonstrate that exogenous inositol improved efficiency of gain in weaned pigs to the same level as that observed with super-dosing phytase, but this occurred only during the first 10 d of the nursery period. This suggests that the improvement in efficiency of growth when applying super-dosing phytase could be linked, in part, to complete dephosphorylation of phytate and liberation of myo-inositol, and that myo-inositol had a greater metabolic impact in piglets immediately after weaning. Consequently, myo-inositol may be a conditionally essential nutrient for young pigs during weaning stress, but further research is needed to prove this hypothesis.