Comparision of corn and barley with and without ruminal buffer in supplements fed in wheat straw-based diets to beef steers

Ruminal fiber digestion is often decreased by supplementation of readily fermentable carbohydrates. Five ruminally cannulated beef steers were used in a 5 X 5 Latin square design to evaluate the effects of grain type (corn vs barley) and ruminal buffer (Na sesquicarbonate; 0 vs 1.2% of dietary DM) on ruminal digestion and fermentation in wheat straw-based diets. Grain supplements were 30% of the dietary DM. The 2 X 2 + 1 factorial arrangement of treatments included a control supplement that consisted primarily of soybean meal. Diets were fed once daily and were formulated to be 10% CP (DM basis). In situ DM (ISDMD) and NDF (ISNDFD) disappearance of wheat straw was measured at 0, 8, 16, 24, 32, 40, and 96 h of incubation. To examine the effects of time after supplementation, 8-h incubations were performed at 0 to 8, 4 to 12, 8 to 16, 12 to 20, and 16 to 24 h after supplementation. Corn diets resulted in lower (P < .05) ISDMD for the 12- to 20- and 16- to 24-h periods than did barley diets. Averaged across 8-h intervals, the control treatment had greater ISDMD (P < .01) and ISNDFD (P < .05) than the grain treatments. Treatment differences were not observed for ISDMD and ISNDFD after 8 h of incubation. Ruminal fluid pH for barley diets was greater at 0, 16, and 20 h and less at 4 h after feeding than for corn diets (treatment X hour; P < .01). Propionate concentration was greater (P < .05) for corn than for barley diets. Buffer addition increased acetate concentration, acetate:propionate ratio, and total VFA concentration for barley diets, whereas a reverse trend was observed for corn diets (grain type X buffer; P < .10). Results of this study demonstrate only subtle changes in ruminal fiber digestion and fermentation as affected by grain type and buffer addition.