Phosphorus (P) and calcium (Ca) are essential minerals for adequate bone development in pigs. The 41-day study evaluated the effect of apparent total tract digestible P levels (dP = 2.5, 3.5, 4.5 and 5.5 g/kg diet containing 14 MJ digestible energy/kg diet) on growth performance and minerals status of 56 weaned piglets (7.6±1.2 kg body weight). Monocalcium phosphate was used as supplemental P source and the dietary Ca to digestible P ratio was fixed at 2.8. Measured individual parameters were weekly feed intake and body weight, serum analytes, metacarpal III and IV mineral concentration and tibia breaking strength and mineral density by dual-energy X-ray absorptiometry (DXA). Feed intake (561±117 g/d) and body weight gain (345±85 g/d) were independent of dP levels, but feed conversion ratio was impaired (P<0.01) in the 4.5 and 5.5 compared to the other dP levels. Blood serum Ca (2.96±0.20 mmol/l), P (3.03±0.39 mmol/l) and alkaline phosphatase activity (286±51 U/l) were not affected by dP levels. Metacarpal ash content was 5% lower in the 2.5 than in the 3.5 dP group and 5% lower (P<0.01) in the 3.5 than in the 5.5 dP group. Metacarpal ash increased linearly (P<0.05) with increasing daily dP intake. Metacarpal Zn content was not affected by increasing dietary Ca and P. Tibia breaking strength, DXA mineral contents and DXA mineral density were improved (P<0.001) with increasing dP levels. With increasing daily dP intake, tibia breaking strength and DXA tibia mineral content and mineral density increased linearly (P<0.001) and DXA tibia mineral density increased quadratically (P<0.01). Tibia breaking strength and DXA mineral content and mineral density were positively correlated (R2 = 0.89 and 0.78 respectively, P<0.001). A dP level of 3.5 g/kg allowed a maximal growth efficiency while greater levels of dP further improved bone mineralization and physical bone parameters. Finally, bone mineral density measured by DXA may present an alternative measurement for bone characteristics to the labour intensive breaking strength measurements.
