Intake and ruminal fermentation by beef steers consuming prairie hay with supplements containing combinations of corn, soybean hulls, soybean meal and urea

Twelve ruminally cannulated beef steers (408±17.2 and 418±15.4 kg initial and final body weight, respectively) fed prairie hay were used to evaluate the effects of substituting soybean hulls for one-half the corn in a urea-based protein supplement on forage intake and ruminal fermentation during two periods. Treatments (three steers treatment^-1) were no supplement (CON), corn plus soybean meal (CS), CS plus urea (CU) and CU plus soybean hulls (SU). Urea provided approximately 35% of the total crude protein (CP) for the CU and SU supplements. Supplements were fed at approximately 145% of maintenance CP requirements. Periods consisted of 14 d for adaptation to the supplement and 7 d for intake measurements. On d 22 of each period, ruminal samples were collected at 0, 0.5, 1, 2 and 4 h after supplementation. Following the 4-h sample, ruminal contents were removed for determination of dry matter (DM) fill and indigestible acid detergent fiber (IADF) passage and fill. Forage and total DM intake did not differ (P>0.10) among treatments. Passage rate of IADF was greater (P<0.10) for CS than for the average of CU and SU. Ruminal DM fill and IADF fill were greater (P<0.10) for the average of CU and SU than for CS. Ruminal pH was not affected (P>0.10) by treatments. At 0.5 h after supplementation (treatment x sampling time, P<0.10) acetate was increased (P<0.05) for CS vs. the average of CU and SU. Across sampling times, propionate was increased and the acetate:propionate ratio was decreased (P<0.10) for the average of CU and SU vs. CS. Ruminal ammonia concentration was increased (P<0.10) by supplements compared with CON at all sampling times. Ammonia concentration was greater (P<0.01) for the average of CU and SU than for CS at 0.5, 1 and 2 h after supplementation, and increased (P<0.10) for SU vs. CU at 0.5 h, Results suggest that soybean hulls can replace corn in urea-based protein supplements without adversely affecting intake or ruminal fermentation, albeit no benefits were noted from the substitution.