Effects of phosphorus and calcium depletion on growth performances and bone mineralisation in growing pigs

The use of P nowadays is raising environmental (eutrophication) and sustainability (limited resource) concerns in the swine industry, but initial trials have shown that similar growth performance can be achieved between pigs fed on a requirement basis and those fed using a P depletion-repletion strategy. To optimise the use of dietary P by pigs, three feeding strategies were studied according to a 3-phase feeding programme: (1) C–C–C providing 100% of the P and Ca requirements, (2) C-L_Normal-C, providing 100% of the P and Ca requirements in phases 1 and 3 (C) with a depletion in phase 2 with 60% of the P requirements combined with a normal Ca:digP ratio of 2.6 (L_Normal), and 3) C-L_High-C, providing 100% of the P and Ca requirements in phases 1 and 3 (C) with a depletion in phase 2 with 60% of the P requirements combined with a high Ca:digP ratio of 3.3 (L_High). Bone mineral content (BMC) and BW were measured at the beginning and end of each phase. BMC gain, average daily gain, average daily feed intake and feed efficiency were calculated for each phase. In phase 1, all pigs received the same diet. At the end of phase 2, the C-L_Normal-C and C-L_High-C groups had similar BMCs compared to the C–C–C group. Finally, at the end of phase 3, the BMC gain was numerically higher in the C-L_Normal-C group than in the C–C–C group (25.4 vs 18.7 g/d, P = 0.10). Although depletion did not cause a decrease in BMC in the C-L_Normal-C and C-L_High-C groups (versus C–C–C), it did result in better P use during repletion. These results demonstrate the value of a depletion-repletion strategy to reduce P intake and excretion without compromising the final performance.