Sorghum grain flake density and source of roughage in feedlot cattle diets

Feedlot performance was studied in a 262-d trial using 126 crossbred beef s teers (182 kg initial BW) to determine whether source of dietary roughage i nfluences performance and carcass characteristics by steers fed growing (11 2 d) and finishing (150 d) diets with various flake densities (FD) of steam -processed sorghum grain. A 3 x 3 arrangement of treatments two pens of sev en steers each) was used, with dietary roughages being chopped alfalfa hay or 50:50 mixtures (equal NDF basis) of cottonseed hulls or chopped wheat st raw with alfalfa fray; sorghum grain was steam-flaked to densities of 386, 322, and 257 g/L (SF30, SF25, and SF20, reflecting bushel weight in pounds) . The effects of these same FD on nutrient digestibilities were determined in three experiments with 24 crossbred steers fed finishing diets containin g each of the roughage. sources. No interactions between FD and roughage ty pe were detected in any performance or carcass measurements (P > .10). Inta ke of DM decreased linearly (P < .05) in response to decreased FD. Daily ra te and efficiency of gain were not altered (P > .16) by FD. Decreasing FD d ecreased linearly (P < .05) dressing percentage and fat thickness, but not other carcass measurements. Dietary roughage did not affect (P > .10) daily gains or carcass measurements, but DM intake was lower and feed efficienci es were superior (P < .05) when alfalfa hay was the sole source of roughage . Cottonseed hulls and wheat shaw were relatively less valuable in the low roughage finishing diets than in higher roughage growing diets, Digestibili ties of starch increased linearly as FD was decreased (P = .02) when steers were fed diets containing wheat straw, but not for alfalfa hay or cottonse ed hull diets. Digestibilities of DM did not vary with changes in FD; howev er, changes in CP, NDF, and ADF digestibilities due to FD seemed to differ among experiments. In conclusion, performance and carcass measurement respo nses by growing-finishing steers to differences-in sorghum grain FD were no t related to source of dietary roughage, but diets with alfalfa hay as the only source of roughage were most efficient. Decreasing FD of sorghum grain below 386 g/L (30 lb/bu) was not advantageous in improving performance or carcass merit by growing-finishing steers.