Practical parameters for assessing starch digestion and feeding value of steam-flaked corn in finishing diets for feedlot cattle

Six Holstein steers (153 kg +/- 11) with cannulas in the rumen and proximal duodenum were used in a 6 x 6 Latin square design experiment to compare flake density (FD, kg/L), flake thickness (FT, mm), amyloglucosidase reactivity (AGR, % DM) and faecal starch (FS, % DM) as predictors of ruminal (RSD, %) and total tract (TSD, %) starch digestion. Dietary treatments consisted of a finishing diet containing 77% corn. The six corn processing treatments consisted of dry-rolled corn (DRC) with a density of 0.54 kg/L, and steam-flaked corn (SFC) processed to obtain densities of 0.46, 0.41, 0.36, 0.31 and 0.26 kg/L. Compared with DRC, steam flaking enhanced postruminal (34.2%, P < 0.01) and TSD (7.8%, P < 0.01). Measures of FS were the best single predictor of both ruminal (r (2 )= 0.97) and TSD (r (2 )= 0.98). Whereas AGR was a good predictor of RSD (r (2 )= 0.94), it was less effective than FS for estimation of TSD (r (2 )= 0.91). We conclude that compared with dry rolling, stream flaking markedly enhances the feeding value of corn. To evaluate the consistency of the flaking process, we recommend in addition to the determinations of FD, measurements of FT, starch enzymatic reactivity and FS are useful indicators.