Effects of dietary digestible calcium on growth performance and bone ash concentration in 50- to 85-kg growing pigs fed diets with different concentrations of digestible phosphorus

•The optimal STTD Ca:STTD P ratio for 50- to 85-kg pigs was determined.•Maximizing bone ash requires a greater STTD Ca:STTD P ratio than maximizing growth performance.•Increasing STTD Ca reduces growth performance if P is at or below the requirement.•Pig diets should be formulated based on a STTD Ca:STTD P ratio.•The STTD Ca:STTD P ratio should be around 1.23:1 if STTD P is at the requirement.