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The objective of this current study was to determine the effects of phytase dosing on growth performance, mineral digestibility, phytate breakdown and the level of glucose transporter type 4 (GLUT4) in muscle plasma membranes of weanling pigs. A total of 160 barrows were used in a randomized completely block design and assigned to four treatments for a 7-week study. Depending on the feeding phase, diets differed in dietary calcium (Ca) and phosphorus (P) levels (PC:8 to 6.8g/kg Ca; 7.3 to 6.3 g/kg P; negative control (NC):5.5 to 5.2 g/kg Ca; 5.4 to 4.7 g/kg P). NC diets were supplemented with phytase at 0 (NC); 500 (NC+500 FTU) or 2000 FTU/kg (NC+2000 FTU) phytase units/kg. Blood was collected after fasting (d 48) or feeding (d 49) for measurement of plasma inositol concentrations. On d 49, two pigs per pen were euthanized, duodenal and ileal digesta samples were collected to determine inositol phosphates (InsP6-2) concentrations. High phytase supplementation increased body weight (BW) on d 21, 35 and 49 (P <0.05). Over the entire feeding period, average daily gain (ADG), average daily feed intake (ADFI) and feed efficiency were increased by NC+2000 FTU compared to the other treatments (P <0.05). Postprandial plasma inositol concentration was increased in NC+2000 (P < 0.01), but there was only a tendency (P = 0.06) of a higher fasting plasma inositol concentration in this group. Inositol concentrations in the portal vein plasma (d 49) were not different among treatments. Duodenal digesta InsP5 and InsP6 concentrations were similar in PC and NC, but higher in these two treatments (P < 0.05) than those supplemented with phytase. Phytase supplementation decreased InsP6-4, resulting in increased InsP3-2 and myo-inositol concentrations. Similar effects were found in ileal contents. Compared to NC, phytase supplementation resulted in greater cumulative InsP6-2 disappearance (93.6% vs. 72.8% vs. 25.0%, for NC+2000 FTU, NC +500 FTU and NC, respectively, P < 0.01) till the the distal ileum. Longissimus dorsi muscle plasma membrane GLUT4 concentration was increased by NC+2000 FTU (P < 0.01) compared to NC. In summary, high phytase supplementation increased growth performance of nursery pigs. The higher myo-inositol release from phytate could contribute to the increased expression of GLUT4 in muscle plasma membranes. Further investigation is needed to determine if this is associated with enhanced cellular glucose uptake and utilization.
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