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The efficacy of phytase (Pase) from OptiPhos Plus G (Huvepharma, Peachtree City, GA) was compared to inorganic phosphorus (iP) supplements to assess phosphorus equivalency. In 6 replicate 28-d trials, 288 crossbred F2 (Duroc X LR X LW) pigs (20.0 kg, 6 pigs/pen, 48 pens) were randomly assigned to 1 of 8 diets. Pig sex was balanced within pens. Basal corn-soybean meal diets, formulated to exceed nutrient requirements except for Ca and P, supplied 1.30% lysine from the same amounts of all ingredients. Sand was used to balance variable amounts of monocalcium phosphate and limestone. Diets supplied either 0.061, 0.156, or 0.241% iP from monocalcium phosphate or increments of 250, 500, 750, 1,000 and 1,500 FTU/kg from Pase. All diets were pelleted (160°F, 2.5 tons/hr). The modified pellet durability index averaged 92.8% and 88.7% for all diets in each of 2 mixes. Non-linear growth responses to increments of iP and Pase were detected (P < 0.05). Using nonlinear regression models, maximum gain was calculated at 0.23% iP and 1144 FTU/kg Pase (equivalent to 0.31% available P or 0.38% STTD P). Likewise, from non-linear responses (P < 0.05), maximum response in whole-body bone mineral content (WBBMC) from analysis of dual energy x-ray absorptiometry scans were calculated at 1227 FTU/kg Pase. The maximum Pase response for WBBMC was below expectations and raised concerns for potential Ca limitations in diets at higher Pase supplements. Only linear WBBMC responses (P < 0.001) to iP levels were detected. Responses across iP and Pase treatments for femur bone mineral content reflected the same conclusions as responses to WBBMC. As growth responses to iP and Pase diets were non-linear, simple conversions of phytase activity to phosphorus release was not straight-forward. However, non-linear equations can predict economic values of target levels as a function of ingredient costs.