LAUSR

The objective was to test the hypothesis that standardized total tract digestibility (STTD) of Ca and the response to microbial phytase is constant among different sources of calcium carbonate and different sources of dicalcium phosphate (DCP). In Exp. 1, 80 pigs (19.0 ± 1.9 kg) were placed in metabolism crates and randomly allotted to 10 diets. Four calcium carbonate-containing diets and a Ca-free diet were formulated without or with microbial phytase (500 units/kg diet). Feces were collected for 4 d after a 5 d adaptation period. Data were analyzed using a model that included calcium carbonate source, phytase, and the interaction between source and phytase as fixed effects and replicate as random effect. There were no interactions between phytase and source. The basal endogenous loss (BEL) of Ca from pigs fed phytase was less (P = 0.037) than from pigs fed no phytase. Values for STTD of Ca in calcium carbonate differed (P < 0.05) among the 4 sources, but increased (P < 0.05) if phytase was used (Table 1). In Exp. 2, 40 pigs (14.9 ± 1.3 kg) were allotted to a basal diet where all Ca was supplied by calcium carbonate, 3 diets containing calcium carbonate and DCP, and a Ca-free diet. Pigs were placed in metabolism crates and feces were collected as in Exp. 1. Data were analyzed using a model that included DCP-source as fixed effect and replicate as random effect. Results indicated that the STTD of Ca in DCP was not different among sources. In conclusion, use of microbial phytase reduces the BEL of Ca and increases Ca digestibility in calcium carbonate, but the STTD of Ca varies among sources of calcium carbonate. However, no difference in STTD of Ca among sources of DCP were observed.