The effect of microbial phytase supplementation of sorghum-canola meal diets with no added inorganic phosphorus on growth performance, apparent total-tract phosphorus, calcium, nitrogen and energy utilization, bone measurements, and serum variables of gro

Two experiments were conducted with growing and finishing swine to determine the effect of phytase supplementation of sorghum-canola meal diets without added inorganic phosphorus (iP) on growth performance, apparent total-tract P, calcium (Ca), nitrogen (N), and energy utilization, bone strength, bone ash, serum Ca and P concentrations, and serum phosphatase activity. For Exp. 1, 42 crossbred barrows in individual metabolism cages were fed a P-deficient diet for 7 d before starting a 28-d experiment at 24.8 kg body weight (BW). Experiment 1 had 7 treatments that were a negative control (NC) diet supplemented with 0, 400, 800, 1200, or 1600 U of Aspergillus niger (AN) phytase/kg, a positive control (PC) diet, and the PC diet supplemented with 1200 U of AN phytase/kg. Fecal and urine collections were made from d 21-26. Blood samples were collected on d 0, 14, and 28. For Exp. 2, 126 growing-finishing crossbred swine with an initial BW of 21.6 kg were group-fed (3 pigs/pen) in 3 phases (grower, early-finisher, and late-finisher). Experiment 2 had 6 treatments that were a NC diet for each phase supplemented with 0, 200, 400, 600, or 800 U of AN phytase/kg and a PC diet. Fecal collections were made from d 49-54. Blood samples were collected on d 35, 63, and 91. For both experiments, 400 U of AN phytase/kg of diet was adequate (P ≤ 0.05) for growth performance compared with the PC treatment groups. For Exp. 1, apparent total-tract P absorption and retention plateaued at 1200 U of AN phytase/kg of diet (P < 0.01), with fecal Ca and P excretion reduced 22.4% and 28.6%, respectively, compared with the PC treatment group. However, pigs fed the PC + 1200 U of AN phytase/kg absorbed and retained more P (g/d, P < 0.01) than any other treatment group. For Exp. 2, apparent total-tract P absorption, bone strength, and bone ash weight plateaued at 600 U of AN phytase/kg of diet (P < 0.01), with fecal P excretion reduced 29.4% compared with the PC treatment group. For both experiments, the AN phytase treatments did not increase Ca, N, or energy absorption (amount/d or % of intake), and had no effect on serum Ca and P concentrations, or the serum activity of alkaline phosphatase, total acid phosphatase, or tartrate-resistant acid phosphatase.