Abstract
Work was carried out to determine the effects of limestone (LM) geometric mean diameter (GMD), phytate, Ca source, and phytase on standardized ileal digestibility (SID) of Ca and P in broilers. Twelve treatments (TRT) were tested. One basal corn and corn germ-based diet was prepared without adding inorganic Ca or P (TRT1, 0.02% Ca). Limestone from the same source (800 or 151 μm GMD) and bone (151 μm GMD) were added to TRT 2-4, (0.7% Ca). TRT5 was a corn/soybean meal (SBM) diet with 800 μm GMD LM (0.77% Ca). Buttiauxella sp. phytase was added (1,000 U/kg) to TRT 1-5 to prepare TRT 6-10, respectively. In addition, 800 or 150 μm GMD LM and monosodium P were added to a nitrogen-Ca-phytate-free diet (TRT 11 and 12, respectively). Treatments were analyzed as a complete block design using SAS mixed procedures and with factorial analysis on subsets of data: 1) LM GMD (151 vs. 800 μm GMD) with or without phytase: TRT 2, 3, 7, and 8; 2) phytate (corn or corn-free) with the same LM at 2 different sizes: TRT 2, 3, 11, and 12; 3) Ca source (LM vs. bone) with or without phytase: TRT 2, 4, 6, 8, and 9; 4) phytate source (corn vs. corn/SBM) with or without phytase: TRT 2, 5, 7, and 10. Broilers (4/pen) were fed mash diets ad lib for 36 h (20-22 d of age). At the end of the trial, distal ileal digesta were collected. Fine LM had lower SID Ca (38.09%) vs. coarse LM (49.18%), irrespective of phytase (P < 0.05). Standardized ileal digestibility of P was lower when the smaller LM was used vs. coarse LM with either 0 or 1,000 phytase U/kg (P < 0.05). Both SID Ca and P were higher without phytate vs. when phytate from corn was present (P < 0.05). Ca from bone was more digestible and its impact on SID P smaller vs. LM regardless of phytase (P < 0.05). In addition, phytate from SBM was more digestible and responsive to phytase as compared to phytate from corn (P < 0.05). In conclusion, dietary factors affected Ca and P digestibility and their response to phytase inclusion.