Research Note: Evaluation of a precision-fed rooster assay for determination of phytic acid disappearance in feedstuffs

The objective of this study was to evaluate a precision-fed rooster assay that is suitable for determination of phytic acid (myo-inositol 1,2,3,4,5,6-hexakis; InsP(6)) disappearance in plant-based feed ingredients. A 48-h precision-fed rooster assay was used to measure InsP(6) disappearance using conventional White Leghorn roosters. A minimum of 4 individually-caged roosters per treatment were fasted for 26 h prior to crop intubation with 15 to 30 g of sample, and excreta 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 (WM) and rice bran (RB) were evaluated without and with 1,000 and 1,800 U/kg phytase in Experiment 2. Data from Experiment 1 were subjected to a one-way ANOVA for a completely randomized design, while data from Experiment 2 were subjected to two-way ANOVA for a 2 × 3 factorial arrangement of treatments. In Experiment 1, InsP(6) disappearance ranged from 3 to 95% among all ingredients. The InsP(6) disappearance for conventional DDGS (95%) was the highest (P < 0.05), wheat bran and soybean hulls were intermediate (47–48%), PKM was low (24%), and soybean meal and canola meal were very low (3–5%). In Experiment 2, there was a significant ingredient × phytase interaction (P < 0.05). Phytase inclusion at both 1,000 and 1,800 U/kg resulted in a significant improvement (P < 0.05) in InsP(6) disappearance for RB; however, only the addition of 1,800 U/kg resulted in an increase in InsP(6) disappearance for WM. The addition of 1,800 U/kg phytase increased the InsP(6) disappearance from 58 to 74% for WM and from 26 to 53% for RB. These results suggest the precision-fed rooster assay can be used to evaluate phytic acid disappearance in plant-based feed ingredients and the assay was able to detect a significant effect of 1,800 U/kg of exogenous phytase on phytic acid disappearance for WM and RB.