Roughage Source and Level in Beef Cattle Finishing Diets¹

Three experiments were conducted to evaluate the effects of roughage level and source in beef cattle finishing diets. In Exp. 1,228 crossbred beef heifers (initial BW. = 346 kg) were fed diets containing 7.5 or 15% roughage (DM basis), with alfalfa hay, sudangrass hay, or cottonseed hulls as roughage sources. Daily gain was not affected (P > 0.10) by roughage level, but DMI was increased (P < 0.10) with 15 vs 7.5% roughage. Among roughage sources, daily gain was less (P < 0.05) with alfalfa than with cottonseed hulls or sudangrass. Dry matter intake was greater (P < 0.05) with sudangrass than with alfalfa and intermediate with cottonseed hulls. Feed:gain did not differ (P > 0.10)among roughage sources, but heifers fed alfalfa were least efficient. In Exp. 2, 224 crossbred beef steers (initial BW = 308 kg) were fed 90% concentrate diets with either whole-shelled or steam-flaked com as grain sources and either alfalfa hay or sudangrass hay as roughage sources. Daily gain was not affected by grain source, but DMI and feed:gain were greater (P < 0.01) with whole-shelled than with steam-flaked com. Similarly, gain did not differ (P > 0.10) between sudangrass and alfalfa, but steers fed sudangrass had greater (P < 0.02) DMI and were less efficient (P < 0.03) than those fed alfalfa as the roughage source. In Exp. 3, 132 crossbred steers (initial BW = 313 kg)were used in a randomized block design with different roughage sources and levels, including: alfalfa hay at 10% of dietary DM or sudangrass hay at 5, 7.5, and 10% of dietary DM. Daily gain was greater (P < 0.06) with diets containing sudangrass than with the alfalfa diet, but level of sudangrass did not affect (P > 0.10) daily gain. Daily DMI was increased (P < 0.03) for diets with sudangrass vs alfalfa, and responded quadratically (P < 0.11) to sudangrass level, with maximum DMI at 7.5% sudangrass. Feed:gain did not differ between the roughage sources but increased linearly (P < 0.11) with increasing level of sudangrass. These results indicate that roughage level and source alter DMI and performance by finishing beef cattle. Sudangrass hay consistently increased DMI relative to alfalfa hay in high-concentrate beef cattle finishing diets, but responses in daily gain and feed efficiency were not consistent between these two roughages. Further research is needed to characterize the relationship between chemical and physical characteristics of roughages and finishing beef cattle performance.