Effects of roughage inclusion and particle size on performance and rumination behavior of finishing beef steers1

Roughage is typically mechanically processed to increase digestibility and improve handling and mixing characteristics in beef cattle finishing diets. Roughage is fed to promote ruminal health and decrease digestive upset, but inclusion in finishing diets is limited due to the cost per unit of energy. Rumination behavior may be a means to standardize roughage in beef cattle finishing diets, and increasing particle size of roughage may allow a decrease in roughage inclusion without sacrificing animal performance. Therefore, the objectives of this study were to quantify rumination time for a finishing beef animal and to evaluate the effects of corn stalk (CS) inclusion rate and particle size on rumination behavior, animal performance, and carcass characteristics. Fifty-one individually fed steers (385 ± 3.6 kg initial BW) were used in a randomized complete block design feeding study. Corn stalks were passed through a tub grinder equipped with a 7.62-cm screen once to generate long-grind CS (LG-CS) or twice to generate short-grind CS (SG-CS). Dietary treatments were based on steam-flaked corn and included, on a DM basis, 30% wet corn gluten feed (WCGF) with 5% SG-CS (5SG), 30% WCGF with 5% LG-CS (5LG), and 25% WCGF with 10% SG-CS (10SG). The Penn State Particle Separator was used to separate ingredients and treatment diets and to estimate physically effective NDF (peNDF). On d 70, each steer was fitted with a collar (HR Tag; SCR Dairy, Netanya, Isreal), which continuously measured rumination minutes via a sensory microphone. Long-grind CS contained more (P < 0.01) peNDF than SG-CS, and the 10SG diet contained more (P = 0.03) peNDF than the 5LG and 5SG diets. Dry matter intake was greatest (P = 0.03) for steers consuming 5LG and least for steers consuming 10SG, with cattle consuming 5SG being intermediate. Carcass-adjusted ADG and G:F were greatest (P ≤ 0.03) for steers consuming 5LG and 5SG compared with steers consuming 10SG. Hot carcass weight tended (P = 0.10) to be greatest for steers consuming 5LG and least for steers consuming 10SG, with steers consuming 5SG being intermediate. Dressing percent was greater (P = 0.01) for steers consuming 5LG and 5SG than for steers consuming 10SG. A significant interaction (P < 0.01) occurred for rumination minutes × day. Rumination (min/day) were greatest (P = 0.01) for steers consuming 10SG followed by steers consuming 5LG and was lowest for steers consuming 5SG. Increasing particle size of roughage may be a means to decrease roughage inclusion rate while maintaining rumination and performance.