Effect of reduced dietary non-phytate phosphorus concentration, with or without calcium reduction, in diets supplemented with phytase for weaned piglets from 28 to 63 days of age

The aim of this study was to investigate the impact of reduced dietary non-phytate phosphorus (nPP) or nPP and calcium (Ca) concentrations in diets supplemented with phytase on performance, bone mineralisation and serum parameters of weaned piglets from 28 to 63 days of age. A total of 168 barrows and gilts, weaned at 28 days of age, with an average initial bodyweight of 8.11 +/- 0.61 kg were randomly allocated in a completely randomised block design. Treatments consisted of a positive control and an additional six treatments, in a 3 x 2 factorial arrangement, totalling seven treatments (Trt). The positive control (PC) diet was formulated to meet or exceed the nutrient requirements of pigs weighing 8-30 kg bodyweight, without phytase supplementation, and the six other diets were formulated similar to the PC, except with a reduction in the nPP concentration of 0.065, 0.130 or 0.195% (Phase Feeding 1 (PF1), PF2 or PF3 respectively) or similar to PF1, PF2 and PF3 minus 0.16% Ca, supplemented with 2000 FTU/kg of phytase, with eight replicate pens/Trt of three piglets each, in a three-phase feeding program. From Day 28 to Day 35, the average daily gain was higher (P < 0.05) and the feed conversion rate was lower (P < 0.05) respectively for piglets fed the PC when compared with those fed PF3 and PC treatment minus 0.160% calcium and minus 0.195% nPP (PF6). In contrast, when evaluating the period from Day 28 to 49, piglets fed PC presented the highest average daily gain, but only differed (P < 0.05) to those fed PF3 and PF6. When considering the overall period, at 63 days of age, no significant difference was detected (P > 0.05) between the PF Trts tested and the PC regarding performance. As for bone mineralisation at 63 days, bone P (BP) decreased as nPP in the diet decreased, regardless of the Ca level. However, except for PF3 and PF6, BP and third metacarpal bone ash concentration were respectively higher for pigs fed the PF Trts, when compared with PC. All treatments containing phytase resulted in a lower bone Ca : BP ratio when compared with PC. Serum P concentrations decreased as nPP in the diet decreased, regardless of the level of dietary Ca. However, with the exception of PF3 and PF6, serum P was not significantly different than pigs fed the PC. In conclusion, reducing nPP or nPP and Ca in diets containing 2000 FTU Ronozyme (R) HiPhos/kg phytase had no adverse effects on growth performance and increased BP and third metacarpal bone ash concentration compared with pigs fed a nutritionally adequate control diet.