Digestibility of calcium in calcium carbonate varies among origins, but is increased by microbial phytase regardless of origin

The objective of this experiment was to test the hypothesis that there are differences in the apparent total tract digestibility (ATTD) of Ca and in the response to microbial phytase among sources of Ca carbonate produced in different regions of the world. Three hundred and twenty barrows (body weight: 17.47 ± 1.28 kg) were allotted to 40 diets using a completely randomized block design with eight blocks of 40 pigs for a total of eight replicate pigs per diet. All diets were based on corn and potato protein concentrate. Twenty sources of Ca carbonate were obtained from different regions of the world, including the United States, Europe, Asia, and South Africa. Each source of Ca carbonate was used in two diets, one diet without microbial phytase and one diet that contained 1000 phytase units (FYT)/kg of diet. Pigs were housed individually in metabolism crates and were fed experimental diets for 12 days, with the initial five days being the adaptation period. Daily feed allotments were divided into two equal meals and pigs were provided feed at 3.0 times the maintenance requirement for metabolizable energy. Feces were collected for four days following the adaptation period, and at the conclusion of the experiment, fecal samples were dried, ground, and analyzed for Ca and P. Results indicated that there were no interactions between source of Ca carbonate and phytase. Differences in ATTD and standardized total tract digestibility (STTD) of Ca were observed among pigs fed diets containing different sources of Ca carbonate (P < 0.001). Pigs fed diets containing 1000 FYT/kg had greater (P < 0.001) ATTD and STTD of Ca compared with pigs fed diets containing no phytase (0.809 vs. 0.697 and 0.835 vs. 0.753, respectively). There was a tendency (P = 0.050) for source of Ca carbonate to influence ATTD of P, and pigs fed diets containing 1000 FYT/kg had greater (P < 0.001) ATTD of P compared with pigs fed diets without phytase (0.793 vs. 0.641). No interactions were observed between region and phytase. The ATTD and STTD of Ca in Ca carbonate from the United States was less (P < 0.05) than in Ca carbonate from Europe, Asia, or South Africa. In conclusion, differences in ATTD and STTD of Ca were observed among Ca carbonate obtained from four regions of the world, and inclusion of microbial phytase increased the ATTD and STTD of Ca in Ca carbonate regardless of the region where the Ca carbonate was produced.