Compensatory effect of dietary phosphorus on performance of growing pigs and development of bone mineral density assessed using dual energy X-ray absorptiometry

Two experiments were conducted using nursery and grower–finisher pigs and dual energy X-ray absorptiometry to monitor the ability of pigs to compensate in area bone mineral density (aBMD; g/cm2) in response to the levels of dietary digestible P following a period of P insufficiency. In experiment 1, 48 female pigs were selected at 8.1 ± 1.0 kg and individually allocated to one of four treatments. The treatments were: high–high (HH) digestible P (3.7 g digestible P/kg for 28 days followed by 3.5 g digestible P/kg for 28 days); high–low (HL) digestible P (3.7 g digestible P/kg for 28 days followed by 2.5 g digestible P/kg for 28 days); low–high (LH) digestible P (3.0 g digestible P/kg for 28 days followed by 3.5 g digestible P/kg for 28 days); and low–low (LL) digestible P (3.0 g digestible P/kg for 28 days followed by 2.5 g digestible P/kg for 28 days). The aBMD was measured at days 0, 28 and 56. In experiment 2, 32 female pigs were selected at 34.0 ± 2.0 and individually allocated to one of four treatments until slaughter at about 102 ± 2 kg live weight. The treatments were: HH digestible P (2.8 g digestible P/kg fed for 35 days followed by 2.3 g digestible P/kg fed to slaughter); HL digestible P (2.8 g digestible P/kg diet fed for 35 days followed by 1.6 g digestible P/kg fed to slaughter); LH digestible P (1.6 g digestible P/kg fed for 35 days followed by 2.3 g digestible P/kg fed to slaughter); and LL digestible P (1.6 g digestible P/kg fed for 35 days followed by 1.6 g digestible P/kg fed to slaughter). The pigs were scanned at days 0, 35 and 70, and a third metacarpal was collected at slaughter for analysis. At day 56 in experiment 1 the left and right hind aBMD was higher (P < 0.05) in pigs fed with HH than HL and LL diets. At day 70 in experiment 2, the whole body aBMD was higher in pigs fed with the HH diet compared to all other treatments (P < 0.001). In conclusion, reducing digestible P fed to nursery pigs for 56 days decreased hind limb aBMD. Replacing low-P with a high-P diet after 35 days in grower–finisher pigs did not result in the similar aBMD to those fed with the high-P diet throughout the nursery and grower–finisher phases.