Su A Lee, a Ph. D. student in the Stein lab, presents the findings of two experiments in which she compared inorganic calcium sources from different suppliers. In the first, she determined the STTD of calcium and the response to the addition of microbial phytase using three sources of calcium carbonate. In the second, she determined the STTD of calcium in three sources of dicalcium phosphate. Adapted from a presentation at the 2019 ASAS Midwestern Section meeting, Omaha, NE, March 11-13.