PSIV-B-23 Late-Breaking: Detection of dietary external markers using portable X-ray fluorescence spectrometry for estimation of digestibility in beef cattle

Abstract

Abstract The use of portable X-ray fluorescence (PXRF) spectrometry to detect dietary external markers on processed or unprocessed bovine fecal specimens to estimate apparent total tract digestibility (ATTD) was evaluated. Seven beef crossbred, ruminally-cannulated steers (BW = 520 ± 30 kg) were used in a completely randomized design. Steers were individually fed a steam-flaked corn-based finishing diet ad libitum for 21-d. Degradable gel capsules containing 7.5 g of titanium dioxide and chromic oxide were placed inside the rumen through the ruminal-cannulae twice daily, throughout the experiment. Fecal samples were collected twice daily from d 14–21, stored frozen (-20oC), and thawed on d-21 to make a composite sample per steer/day. Wet chemistry analyses of fecal samples included atomic absorption for Cr and spectrophotometry for TiO2 and were compared with PXRF to determine the concentration of these markers on three types of fecal specimens: fresh (average 22.5 % DM), dried (60oC, 72 h), or dried/ground (1 mm). Data were analyzed using the GLIMMIX procedures of SAS with collection day as a repeated measure. Delta between ATTD estimated by wet chemistry and PXRF was not different from zero when using fresh fecal specimens analyzed for Cr (P = 0.40) or Ti (P = 0.14), while for dried or dried/ground specimens it differed (P ≤ 0.04), in which ATTD was underestimated by 3.6 and 1.1 percent units for Cr and Ti, respectively, when using PXRF. Concentration of Ti in fecal specimens was similar (P = 0.39) between analytical methodologies regardless of sample preparation. However, concentration of Cr was underestimated (P < 0.01) by 13% when PXRF was used in dried or dried/ground fecal samples compared to wet chemistry. Detection of Cr and Ti in fresh fecal samples with PXRF spectrometry seems to be a viable alternative to wet chemistry for estimating ATTD for finishing steers.