A Digestibility of Phosphorus and Calcium in Pig Diets experiment was conducted to determine if the area in which soybeans are grown influences the concentration of phosphorus (P), phytate, and macro- and micro-minerals in the soybean meal (SBM) produced from the beans and, therefore, also influences the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P in SBM. The second objective was to test whether including microbial phytase in the diet will increase the ATTD and STTD of P in SBM regardless of where the beans were grown.

Twenty sources of SBM were procured from crushing facilities located in different regions of the United States that were separated into three zones: 1) the northern growing area (Michigan, Minnesota, and South Dakota), 2) the eastern growing area (Georgia, Illinois, Indiana, and Ohio), and 3) the western growing area (Iowa, Missouri, and Nebraska). For each source of SBM, two diets based on cornstarch and SBM were formulated; one of these diets contained no microbial phytase and the other diet contained 500 units/kg of microbial phytase. Two hundred growing barrows weighing about 16.9kg were individually placed in metabolism crates and allotted to a randomized complete block design with 40 diets and five replicate pigs per treatment. Feces were collected for four days after a four-day adaptation period using the marker-to-marker procedure.

Results indicated that there were no differences in concentration of Ca, P, phytate, and macro- and micro-minerals among SBM from the different zones. However, there was a tendency (P = 0.055) for an increase in concentration of nonphytate P in SBM from the western growing area (0.25%) compared with SBM from the northern growing area (0.23%) and the eastern growing area (0.23%). There were no differences in feed intake, absorbed P, ATTD of P, STTD of P, Ca intake, Ca output, or ATTD of Ca for pigs fed SBM from the three zones. However, there was a tendency (P = 0.066) for an increase in P intake and P output from pigs fed SBM from the western growing area compared with pigs fed SBM from the northern growing area. There was an increase (P ‹ 0.05) in absorbed P, ATTD and STTD of P, and ATTD of Ca when microbial phytase was included in the diets, however, the quantity of P and Ca excreted in the feces decreased (P ‹ 0.001) when microbial phytase was included in the feed formulation. In summary, this study showed no differences in ATTD and STTD of P exist among SBM produced in different areas of the United States, and microbial phytase will increase the digestibility of P in SBM.