Influence of mechanical maceration on wheat straw on characteristics of digestion in growing-finishing diets for feedlot cattle

Four Holstein steers (142 ± 3 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square design to evaluate the influence of mechanical maceration of wheat straw on the characteristics of digestion. Treatments consisted of a steam-flaked corn-based growing-finishing diet supplemented with 21% forage (DM basis) as: 1) sudangrass hay (SG), 2) wheat straw (STRW), 3) macerated wheat straw (MAC) at intensity of 600 psi (MAC600) and 4) macerated wheat straw at intensity of 900 psi (MAC900). All forage treatments were ground to pass through a 3.81 cm screen before incorporation into complete mixed diets. Chromic oxide was used as an indigestible marker to estimate nutrient flows and digestibility. Ruminal NDF kinetics were determined from measures by total evacuation of ruminal content and by NDF duodenal flow. There were no treatment effects (P ≥ 0.11) on ruminal digestion of OM, NDF, starch, microbial efficiency (MN, g/kg of OM fermented), or protein efficiency (NAN, g/g of N intake). Apparent total tract digestion of OM, NDF and DE diet were greater (P < 0.01) for SG than for STRAW. Maceration of wheat straw increased (P < 0.04) apparent postruminal and total tact digestion of OM, NDF, N, and dietary DE. Ruminal NDF passage rate was greater (P ≤ 0.05), and ruminal DM (P < 0.01) and NDF fill (P ≤ 0.02) were lesser for SG and MAC than for STRW. Intensity of maceration (MAC600 vs. MAC900) did not affect (P ≥ 0.11) characteristics of site and extent of digestion. Maceration increased (28%) the DE value of wheat straw. The DE value of MAC tended to be greater (7.5%; P = 0.08) for MAC than for SG.