The objective of this study was to develop a precision-fed rooster assay that is suitable for determination of phytic acid (myo-inositol 1,2,3,4,5,6-hexakis; InsP6) disappearance in plant-based feed ingredients. A 48 h precision-fed rooster assay was used to meas-ure InsP6 disappearance using conventional White Leghorn roosters. A minimum of 4 individually-caged roosters per treatment were fasted for 26 h prior to being precision-fed (crop intubation) between 15 and 30 g of sample. After roosters were precision-fed, excreta (feces + urine) were quantitatively collected for 48 h. Soybean meal, soybean hulls, canola meal, conventional distillers dried grains with solubles (DDGS), palm kernel meal (PKM), and wheat bran were evaluated in Experiment 1, whereas wheat middlings and rice bran were evaluated without exogenous phytase and with 1,000 and 1,800 FTU/kg phytase in Experiment 2. Data from both experiments were subjected to a one-way ANOVA for a completely randomized design. Data from Experiment 2 were also subjected to two-way ANOVA for a 2 × 3 factorial arrangement of treatments with in-gredient (wheat middlings or rice bran) and phytase level (0, 1,000, or 1,800 FTU/kg) as main effect variables. In Experiment 1, InsP6 disappearance ranged from 3 to 95% among all ingredients. The InsP6 disappearance for conventional DDGS (95%) was the highest (P < 0.05), wheat bran and soybean hulls were intermediate (47%), PKM was low (24%), and soybean meal and canola meal were very low (3 to 5%) The InsP6 disappear-ance for wheat middlings and rice bran without exogenous phytase in Experiment 2 was 58% and 26% respectively, which was increased (P<0.05) to 74% and 53% with the addition of 1,800 FTU/kg phytase, respectively. In Experiment 2, there was a significant ingredient × phytase interaction (P < 0.05). Thus, the inclusion of phytase at both 1,000 and 1,800 FTU/kg resulted in a significant improvement (P < 0.05) in InsP6 disappear-ance for rice bran; however, only the addition of 1,800 FTU/kg phytase resulted in an increase in InsP6 disappearance for wheat middlings. The InsP6 disappearance for wheat middlings and rice bran without exogenous phytase in Experiment 2 was 58% and 26%, respectively, which was increased (P < 0.05) to 74% and 53% with the addition of 1,800 FTU/kg phytase, respectively.