Effect of a Phosphate-free Diet Supplemented with Phytase on the Growth Performance and Mineralization of Growth Pigs

Abstract About 70% of plant phosphorus (P) occurs as poorly digestible phytate in pigs. Phytase supplementation in a phosphate-free diet improved P utilization, though it affected bone mineralization early in the fattening period. The objective of this study was to evaluate the effect of a high phytase incorporation in phosphate free diet on bone mineralization and growth performance in pigs. To this end, 144 pigs (35 kg initial body weight) were randomly allocated to 24 pens of six animals each. The animals received one of three dietary treatments over three consecutive phases (21, 28 and 25days): control diet (CTRL; Ca : P1=8.6; P2=6.5; P3=5.4 / P dig : P1=3.1; P2=2.2; P3=1.9 g.kg), phosphate diet (PHOS; Ca : P1=11.5; P2=8.4; P3=7.6 / P dig : P1=4.7; P2=3.0; P3=2.9 g.kg), and phytase diet (PHYT; Ca : P1=7.1; P2=9.2; P3=8.8 / P dig : P1=3.4; P2=2.9; P3=3.3 g.kg) without phosphate (1000 FTU/kg). At the start of fattening, PHYT had digestible P and total Ca contents comparable to CTRL, while in the finishing phase, its P level matched PHOS. Growth performance was recorded for each phase. One pig per pen was scanned using dual-energy X-ray absorptiometry (DEXA) to determine bone mineral content (BMC) at the beginning and end of each phase. These values were then converted into body P and Ca contents. Simultaneously, blood samples were collected to measure plasma P and Ca concentrations. Data were analysed using a linear mixed model for repeated measures. Fixed effects included time and treatment, and the experimental unit was treated as a random effect. Dietary treatments had no effect on growth performance. A time × treatment interaction was observed for BMC (P 0.001). On day 21, pigs in the PHOS tended to have a higher BMC (g) than those in the PHYT group (+20%; P = 0.07), while pigs in the CTRL group showed intermediate values (+15%). On days 49 and 73, pigs in the PHOS had a higher BMC than those in the CTRL (day 49 : +18%; P = 0.017/ day 73 : +18%; P = 0.0007), whereas pigs in the PHYT were intermediate at day 49 (+9% vs control) and similar to those in the PHOS at day 73 (+17% vs control; P = 0.0021). At day 49, the plasma Ca/P ratio was significantly lower in the CTRL than in the PHYT and PHOS treatments (P = 0.04). During phases 1 and 2, dietary treatments affected the efficiency of digestible phosphorus utilization for BMC deposition (respectively, P = 0.01; P = 0.03) with X being the most efficient, whereas calcium utilization efficiency was not influenced. Overall, the results demonstrate the feasibility of phosphate-free feeding strategies without compromising growth performance or bone mineralization in pigs.