Digestibility and Utilization of Mechanically Processed Soybean Hulls by Lambs and Steers

A steer and two lamb digestion trials and a steer growth trial were conducted to evaluate the effects of mechanical processing on the digestibility and utilization of soybean hulls (soyhulls). Whole toasted soyhulls or corn replaced ensiled cornstalks in the steer digestion trial. Neutral detergent fiber intake increased as level of soyhulls increased, but it decreased with corn additions. Rate of solka floc NDF digestion (in situ) decreased linearly (P < .001) as energy level increased, as did ruminal pH (pH range at 12 h postfeeding = 6.6 to 5.9). In lamb Trial 1, pelleting increased soyhull bulk density by nearly fourfold. Feeding ground (1.5-mm screen) soyhulls resulted in lower DM and NDF digestibilities than did corn, whole soyhulls or the average of the pelleted soyhull treatments. Lamb Trial 2 evaluated grinding (4.8-mm and 3.2-mm screens), pelleting (9.5-mm and 4.8-mm dies) and combinations of the processes compared with whole soyhulls. No differences in DM or NDF digestibilities were observed among treatments. The growth trial used 168 steers (235 kg) assigned to seven treatments arranged factorially (2 × 3 plus basal control) to evaluate corn, whole soyhulls and ground soyhulls at 1.05 or 2.1 kg DM·hd−1·d−1. Higher energy levels increased daily gains (P < .01), but sources were not different (P = .18). Source and level interacted (P < .05) for feed efficiency. Mechanical processing of soyhulls minimally altered digestibility or feeding value relative to corn, except when finely ground. Soyhulls are a viable alternative to grains as energy supplements to high-forage diets.