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The objectives were to investigate the effect of grain type and a Yucca schidigera extract based product (Grain Prep® surfactant, GP) on ruminal fermentation and ammonia utilization by mixed microbial populations in vitro (Study 1) and ruminal degradation parameters of flaked corn DM and starch in sacco (Study 2). In Study 1, three 8 h incubations were completed with ruminal inoculum from two lactating dairy cows. A GP treated feed mixture, containing alfalfa hay, grain, and soybean meal, was incubated with buffer and ruminal inoculum. The grain part of the feed mixture was either corn (C) or 50:50 corn and high amylopectin barley grain (CB). GP was applied to the feed mix at 0, 60, and 120 ppm (as is basis). At time 0 h, the ammonia pool was labeled with 15N. Inclusion of barley in the grain mixture increased media pH and decreased ammonia concentration (13.0 mM versus 12.7 mM, respectively), but the concentration of total and individual VFA, or incorporation of 15N into bacterial protein, was not affected by grain type, and GP had no effect on ammonia or VFA concentrations. At the incubation end-point (8 h), GP tended (P=0.11) to linearly increase the proportion of bacterial N originating from ammonia N. In Study 2, flaked corn grain produced in a commercial feed preparation facility was treated with GP at 22 ppm (as is basis; GP) or with water (control) and incubated in the rumen of three lactating Holstein cows for 0, 2, 4, 6, 16, 24, 48, and 72 h. Solubility of corn DM and starch increased with GP, compared to the control, by 16 and 18%, respectively. The proportion of potentially degradable DM and starch was reduced, and effective degradability of DM and starch were increased, by GP. A 50% substitution of corn by barley grain had a positive effect on ammonia N utilization in the rumen in vitro. The saponin based surfactant did not affect fermentation or ammonia utilization, but GP treated corn had a higher in sacco degradability of DM and starch in the rumen of lactating dairy cows, mostly due to an increase in the soluble/instantly degradable DM, or starch, with the GP treated corn grain. [Copyright &y& Elsevier]