Effect of phosphorus and calcium depletion and repletion sequences on growth performance, bone mineralization and endogenous phosphorus losses in pigs
The impact of dietary calcium (Ca) and phosphorus (P) deficiency (depletion) and following recovery (repletion) was further studied in 60 castrated pigs from 14±1.6 to 132±10.3 kg BW during four 28-d feeding phases. Pigs received a repletion control diet (C) fulfilling the estimated nutrient requirements or a depletion diet (L) providing 60% of the required digestible P and total Ca in six dietary sequences randomly assigned: CCCC, CCCL, CCLC, CLCC, LCLC and LLLL. Growth performance was measured, and bone mineral content of total body (BMCb) and lumbar vertebrae (L2-L4, BMCv) were estimated by dual x-ray absorptiometry (DXA) in each phase. Additionally, two P-free balance trials were performed on 8 animals during the first (C vs L) and 8 others during the second (CC vs LC) phases to estimate basal endogenous P losses (EPL). Depletion diets reduced average daily gain during the first (L vs C, -7%; P = 0.05) and second (CL vs CC, -7%; linear effect: P = 0.01) feeding phases. Repletion did not entail pigs to perform as control ones during the second (LC vs CC, -5%; P = 0.08) and fourth phases (CCCC vs CCLC vs CLCC vs LCLC; Linear effect: P = 0.05). The decreased BMCb and BMCv observed in depleted pigs were proportional to the number of depletion phases (linear effect: P < 0.001). During the following repletion phases, these pigs retained dietary P more efficiently. Depletion and repletion effects were both more marked in vertebrae than in total body indicating that vertebrae is more sensitive to dietary Ca and P supply. Thereby, BMCv in repleted animals (CCCC, CCLC, CLCC and LCLC) were not different at the end of the experiment whereas a linear effect (P = 0.01) was observed for BMCb. The P-free balance trial showed that EPL were not modified during depletion or repletion periods. Average EPL were of 77.4±3.8 and 132.8±2.2 mg/kg DMI in the first two growing phases, respectively. Depleted pigs used dietary Ca and P more efficiently than control pigs allowing them during the subsequent repletion phases to fully recover BMCv losses at the end of the third phase but just partially BMCb losses at the end of the experiment.
depletion-repletion, phosphorus, pigs