Evaluation of steam-flaked corn bulk density manipulation during grain adaptation of beef steers and the use of X-ray fluorescence spectrometry technique to measure apparent total tract digestibility



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In Exp. 1, 6 ruminally cannulated beef steers were used in a CRBD to evaluate bulk densities of steam- flaked corn (SFC; 335 or 412 g/L; n = 3/ trt) on ruminal fermentation and feeding behavior characteristics. In Exp. 2 and 3 the use of a portable X-Ray fluorescence spectrometry (PXRF) technique to measure apparent total tract digestibility (ATTD) was performed using a CRD on seven ruminally cannulated beef steers and eight sheep. In Exp. 1, steers were fed ad-libitum during 6-7d phases consisting of: Hay; Step-up (1, 2, 3, and 4); and a finisher (Fin) diet. Respective SFC bulk densities were constant throughout phases, except Fin when steers were switched to 412. Ruminal pH average was continuously measured (wireless pH probes), and ruminal fluid was collected. A continuous observation (24 h) was used for feeding behavior. The SFC-BD did not affect (P ≥ 0.19) measured variables, except for greater NDF (P < 0.01) and ADF (P = 0.09, tendency) digestibility observed for 412 g/L steers during Step-up 3. Greater (P ≤ 0.01) digestible DMI during Step-up 4 and Fin were observed compared to other phases. Digestible NDF/ADF intakes were greatest (P ≤ 0.05) during HAY-phase. ATTD was lowest (P ≤ 0.05) during HAY-phase. Steers ruminated and chewed the most (P ≤ 0.05) during HAY-phase. Ruminal C2:C3 decreased (P < 0.01) as steers advanced through phases. The SFC bulk density range studied seems to not dramatically affect ruminal fermentation characteristics and feeding behavior. For experiment 2, steers (BW = 520 ± 30 kg) were individually fed a SFC-based finishing diet ad libitum for 21 d (14 d adaptation, 7 d collection). Degradable gel capsules (7.5 g of TiO2 and Cr2O3) were placed inside the rumen. Fecal samples were collected twice daily and immediately frozen (-20oC). For study 2, sheep (BW = 68 ± 3 kg) were individually fed twice daily a SFC-based diet ad libitum for 21 d (14 d adaptation). After adaptation, sheep were moved to metabolism crates for 7 d (5 d of collection). Cr2O3 and TiO2 (2 g, each) were mixed with 5 g WCGF and top dressed onto feed. Total fecal samples (collection harnesses) twice daily were subsampled (50%) and analyzed for marker concentration using atomic absorption (Cr) or spectrophotometry (TiO2) and compared with the values obtained from the PXRF device. Fecal specimens included: fresh (average 22.5 % DM), dried (60oC, 72 h), or dried/ground (1 mm). For experiment 3, total fecal collection (CON) was used to measure marker fecal recovery. Data were analyzed using the GLIMMIX procedures of SAS. The difference between ATTD estimated by wet chemistry and PXRF was not different from zero when using bovine fresh fecal specimens analyzed for Cr (P = 0.40) or Ti (P = 0.14); whereas PXRF used for dried and dried/ground specimens it differed (P ≤ 0.04), in which ATTD was underestimated by 3.6 and 1.1 % for Cr and Ti, respectively. The ATTD of sheep was underestimated (P < 0.01) by 2.4 % compared with CON when Cr was measured by PXRF in dried-only samples. Fresh and dry/ground fecal samples assessed for Cr, and all samples accessed for Ti were not (P ≥ 0.49) affected by marker detection method. For Ti, dried-only sheep fecal specimens did not differ (P = 0.63) from zero. The use of PXRF seems to accurately detect Cr and Ti in fresh beef steers fecal samples, while dried-only and dry/ground fecal samples showed better accuracy for ovine specimens.



Adaptation, Bulk density, External markers, X-ray fluorescence spectrometer