Supplementation of a wheat-based diet low in phosphorus with microbial 6-phytase expressed in Aspergillus oryzae increases digestibility and plasma phosphorus but not performance in lactating sows

Phosphorus (P) in most diets for sows is poorly digested because pigs do not produce salivary or gastric phytase to hydrolyze P from phytate (inositol hexaphosphate), thus leading to a relatively high amount of P in the manure. An experiment was carried out to study the efficacy of a novel bacterial 6-phytase produced by a strain of Aspergillus oryzae expressing two synthetic genes, both mimicking a phytase gene from a Citrobacter braakii strain. The apparent total tract digestibility coefficient (CATTD) of P, calcium (Ca), crude protein (CP), and gross energy, concentrations of plasma variables, and sow performance were used as response variables. In total, 45 crossbred gestating sows (Large white×Landrace) were individually housed with their litter. Three diets were prepared: (1) positive control (PC; 5.2 g available P/kg), regular sow diet containing inorganic P; (2) negative control (NC; 2.0 g available P/kg) without inorganic P; and (3) NC + 500 FTU/kg diet (NC + PHY). Each diet was fed to 15 sows for 21 days (from day 108 of gestation to day 15 of lactation). To the diets, 3.0 g titanium dioxide/kg was added as a marker to determine CATTD of nutrients. Blood samples were collected from the anterior vena cava at day 1 and 15 of lactation to determine plasma minerals (P, Ca, magnesium, copper, iron, and zinc) and plasma urea, glucose, total protein, albumin, and globulin. At day 15 of lactation, CATTD of P did not differ between PC and NC. Phytase supplementation to NC increased (P<0.05) CATTD of P from 0.34 to 0.46 compared to NC, but did not affect CATTD of CP, gross energy, and Ca. On day 1 of lactation, plasma P was 0.66 mmol/L lower (P<0.05) in sows fed NC than PC. Phytase supplementation to NC increased (P<0.05) plasma P by 0.40 mmol/L on day 1 but not on day 15 of lactation. Sow performance measured as feed intake and body weight changes did not differ between PC and NC or phytase supplementation to NC. In conclusion, phytase supplementation increased P bioavailability in lactating sows. Feeding a P-reduced diet during the first 2 weeks of lactation did not reduce sow performance.