Extra-phosphoric effects of super dosing phytase on growth performance of pigs is not solely due to release of myo-inositol.

Two experiments were conducted to determine the effects of myo-inositol and phytase on growth performance, plasma metabolites and nutrient digestibility of growing pigs. In Exp. 1, 96 growing pigs with average initial body weight (BW) of 26.2 kg were used in a 25-d growth performance study. Pigs were assigned to four dietary treatments with 3 pigs per pen and 8 replicate pens per treatment in a randomized complete block design. The 4 treatments were control diet (CD); CD + 2 g/kg inositol; CD + 1,000 FYT/kg phytase and CD + 3,000 FYT/kg phytase. Pigs were weighed individually every week. On d 25, blood sample was collected from one pig per pen to measure plasma metabolites concentrations. In Exp. 2, sixteen barrows (initial BW 34.8 ± 8.2 kg) were surgically fitted with T-cannulas. Pigs were allotted to 4 blocks based on BW and assigned to a quadruplicate 4 × 2 incomplete Latin square design with same 4 dietary treatments and 2 periods. Ileal digesta samples were collected from each pig on d 6 and 7 of each period to determine apparent ileal digestibility (AID) of nutrients. Phytase supplementation increased final BW and average daily gain (ADG) compared to CD (P < 0.05) with no effects on average daily feed intake (ADFI) and gain to feed (G:F) was higher in 3,000 FYT/kg phytase (P < 0.05). Inositol supplementation had no effects on growth performance. Plasma myo-inositol concentration was increased by inositol supplementation, and 3,000 FYT/kg phytase increased myo-inositol in the plasma by 97.2% (P < 0.05). Plasma P concentration was increased by 1,000 or 3,000 FYT/kg phytase with no effects on alkaline phosphatase (ALP), glucose, triglycerides (TAG), calcium (Ca) and urea concentrations. Phytase supplementation reduced (P < 0.05) the phytate-P concentration in the ileal digesta and increased the digestibility of phytate-P and total P with no effects on the AID of dry matter (DM), gross energy (GE), nitrogen (N) and Ca. In conclusion, the beneficial effects of 3,000 FYT/kg phytase on feed efficiency may due to the increased release of both myo-inositol and phosphorus (P), and may not be solely due to myo-inositol release by this level of phytase.