284 Effect of formulating diets based on a ratio between STTD Ca and STTD P and the inclusion of phytase on growth performance, plasma Ca and P, and bone ash of pigs from 11 to 130 kg

Abstract

Abstract A 126-d experiment was conducted to test the hypothesis that the requirement for Ca expressed as a ratio between standardized total tract digestible (STTD) Ca and STTD P obtained in short-term experiments may be applied to pigs fed diets without or with microbial phytase from 11 to 130 kg. In a 5-phase program, 160 pigs (11.2 ± 1.8 kg) were randomly allotted to 32 pens and 4 corn-soybean meal diets in a 2 × 2 factorial design with 2 formulation strategies (total Ca or STTD Ca), and 2 phytase levels (0 or 500 units/kg) assuming phytase released 0.11% STTD P and 0.16% total Ca. The STTD Ca:STTD P ratios were 1.40:1, 1.35:1, 1.25:1, 1.18:1, and 1.10:1 for phases 1 to 5. At the conclusion of each phase, weights of pigs and feed left in feeders were recorded and a blood sample from 1 pig per pen was collected. At the end of phases 1 (d 24) and 5, the right femur of 1 pig per pen was collected. Data were analyzed as main effects of formulation strategy and phytase level and their interaction. Phase effect was analyzed by repeated measures. No interactions were observed and formulation strategy and phytase did not impact growth performance, bone ash, or plasma Ca and P on d 24 (Table 1). On d 126, an interaction (P < 0.05) between main effects was observed. Without phytase, pigs fed diets based on total Ca had greater bone ash than STTD Ca pigs, but with phytase, no differences were observed. A negative quadratic effect (P < 0.05) of phase for plasma Ca and P was observed. In conclusion, STTD Ca:STTD P ratios can be used in diet formulation for growing-finishing pigs without affecting growth performance. Phytase ameliorates bone resorption caused by low Ca in STTD Ca diets.