Predicting ruminal and total tract starch digestion as influence by changes in density of steam-flaked corn: flake thickness, enzymatic reactivity, fecal starch

Abstract Text: Six Holstein steers (153 kg ± 11) with cannulas in the rumen and proximal duodenum were used in a 6×6 Latin square design experiment to compare flake density (FD, kg/L), flake thickness (FT, mm), amyloglucosidase reactivity (AGR, %), and fecal starch (FS, %) as predictors of ruminal (RSD, %) and total tract (TSD, %) starch digestion. Based on FD, RSD =  92.5 – 36.6FD (r²= 0.76) and TSD = 96.5 + 30.2FD – 68.6FD² (r²= 0.99). Based on FT, RSD =  88.9 – 4.45FT (r²= 0.83) and TSD = 97.1 + 3.77FT – 1.43FT² (r²= 0.99). Based on AGR, RSD = 72.0 + 0.43AGR (r²= 0.94) and TSD = 90.9 + 0.695AGR – 0.0138AGR² (r²= 0.91). Based on FS, RSD = 85.9 – 2.88FS + 0.204FS² (r²= 0.97) and TSD = 100.0 – 0.40FS (r²= 1.00). Measures of fecal starch were the best single predictor of ruminal and total tract starch digestion in catte fed steam-flaked corn-based diets. Fecal starch has the additional advantage of being equally effective when data for dry rolled corn are included in the dataset. Whereas AGR was a good predictor of ruminal starch digestion, it was the least effective of the measures for estimation of total tract starch digestion. Due to the ease of its determination, flake thickness may be the more convenient and reliable measure for assessment of day-to-day process adequacy.

Keywords: starch, maize, digestion