Effects of Super-Dosing Phytase and Inositol Supplementation on Growth Performance and Blood Metabolites of Weaned Pigs Housed Under Commercial Conditions

This study was designed to evaluate if improvements in growth performance associated with super-dosing phytase can be explained by the liberation of inositol through the near complete dephosphorylation of phytate. A total of 2,156 barrows and gilts (BW 6.75±0.11 kg) were used in a 42 d study. Two phytase doses (0 and 2,500 FTU/kg; Quantum Blue, AB Vista) and 3 inositol levels (0, 0.15 and 0.30%) were arranged to create 6 dietary treatments. Pigs were placed in a total of 98 pens (22 pigs per pen: 16 to 17 pens per treatment) and fed a 3-phase feeding program, with each period being 10, 10 and 22 d, respectively. Blood samples were collected on d 0, 21 and 42 from a subset of 48 pigs (8 pigs per treatment) to determine serum concentrations of P, K, Ca, Mg, Zn, Fe, S and Cu and plasma concentrations of inositol. Data were analyzed as a RCBD in a 2×3 factorial arrangement of treatments. During phase 1, increasing inositol in diets without supplemental phytase linearly (P<0.001) improved the G:F ratio (1022, 1040, and 1089 g/kg for 0, 0.15 and 0.30% inositol, respectively), but not in pigs supplemented with phytase (1102, 1087, and 1076, g/kg for 0, 0.15 and 0.30% inositol, respectively; P=0.015, interaction). During phase 2, increasing dietary inositol increased ADFI in diets without supplemental phytase only (interaction, P=0.01; 589, 600, and 612 g/d and 627, 626 and 607 g/d for 0, 0.15 and 0.30% inositol, respectively). Super-dosing phytase to diets without inositol improved (P<0.001) G:F (1102 vs. 1022 g/kg) during phase 1 and improved (P < 0.001) ADG (479 vs. 461 g/d) during phase 2. Phytase increased serum Zn on d 21, but not on d 42 (interaction, P=0.008). Phytase increased serum Cu (2.06 vs. 1.82 mg/L) and reduced serum Fe (0.72 vs. 1.15 mg/L), regardless of day of measurement (P<0.05). Dietary inositol linearly increased plasma inositol concentrations (66.9, 97.1 and 113.2 nmol/mL, respectively; P<0.001), regardless of phytase supplementation. Super-dosing phytase to diets without inositol tended to increase (P=0.064) plasma inositol concentrations (81.4 vs. 56.5 nmol/mL) on d 42. Results suggest that the improvement in performance when applying super-dosing levels of phytase may be partially linked to inositol production and that inositol (supplemented or liberated by phytase) had a greater metabolic impact in piglets immediately after weaning. This suggests that inositol may be conditionally essential for young pigs during the stress of weaning.