COMPARISON 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 readi ly fermentable carbohydrates. Five ruminally cannulated beef steers we re used in a 5 x 5 Latin square design to evaluate the effects of grai n type (corn vs barley) and ruminal buffer (Na sesquicarbonate; 0 vs 1 .2% of dietary DM) on ruminal digestion and fermentation in wheat stra w-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 a nd 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, 3 2, 40, and 96 h of incubation. To examine the effects of time after su pplementation, 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 result ed 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 tre atment had greater ISDMD (P < .01) and ISNDFD (P < .05) than the grain treatments. Treatment differences were not observed for ISDMD and ISN DFD after 8 h of incubation. Ruminal fluid pH for barley diets was gre ater at 0, 16, and 20 h and less at 4 h after feeding than for com die ts (treatment x hour; P < .01). Propionate concentration was greater ( P < .05) for com than for barley diets. Buffer addition increased acet ate concentration, acetate:propionate ratio, and total VFA concentrati on for barley diets, whereas a reverse trend was observed for com diet s (grain type x buffer; P < .10). Results of this study demonstrate on ly subtle changes in ruminal fiber digestion and fermentation as affec ted by grain type and buffer addition.