Dietary Phosphorus Removal with and without Microbial Phytase Addition for Growing Finishing Pigs

One hundred seventy one crossbred pigs (53.3 ± 1.4 kg) were used to evaluate the effects of removing inorganic P from finishing diets with or without phytase addition during two 28-d finisher phases (EARLY and LATE, respectively). Dietary treatments were: 1) control (Trt 1; EARLY 0.49% total P, 0.19% available P (aP); LATE 0.43% total P, 0.15% aP); 2) Trt 1 without inorganic P (Trt 2; EARLY= 0.36% total P, 0.07% aP; LATE= 0.33% total P, 0.06% aP); and 3) Trt 2 + 500 FTU/kg phytase (Trt 3). Average daily gain, ADFI and G:F (g/kg) were calculated every 2 wk. Pigs were scanned for 10th rib fat thickness (FT) and longissimus area (LEA) and values were adjusted to a common BW (104 kg). One male and one female per pen were slaughtered and fourth metacarpal bones collected and ashed. During the EARLY and LATE phases pigs fed Trt 2 had lower ADG and ADFI (P≤0.05; 760 vs. 831 and 2275 vs. 2399 g, respectively) than pigs fed Trt 3. Adjusted FT and LEA did not differ among treatments. Fourth metacarpal dry and ash weights were greater for pigs fed Trt 3 (P