Arya, S. and McKinnon, J. J. 2011. The effects of a low lignin hull, high oil groat oat on the performance and carcass characteristics of feedlot cattle. Can. J. Anim. Sci. 91: 685-693. A study was conducted to evaluate inclusion levels of a low lignin hull, high oil groat oat (CDC SO-I) on the performance and carcass characteristics of feedlot cattle. Two hundred crossbred steers (average weight of 427.3 kg±22.4) fed in 20 pens (10 head per pen) were used. Five treatments, formulated by replacing barley grain with increasing levels of CDC SO-I oat (Barley grain:CDC SO-I oat ratios of 100:0; 75:25; 50:50; 25:75 and 0:100; DM basis) were used. Over the entire study, there was a linear decrease (P<0.01) in DMI and ADG with increasing inclusion level of CDC SO-I oat. There was a quadratic effect (P=0.03) on gain to feed with similar values for steers fed 100:0, 75:25, 50:50 and 75:25 and then decreasing for the 0:100 treatment. Days on feed increased (P=0.03) quadratically with steers fed the 75:25 and 0:100 treatments spending the longest time on feed. Increasing the inclusion level of CDC SO-I oat in the diet also linearly decreased (P<0.01) carcass weight, dressing percentage and carcass grade fat. However, there was no effect of treatment on l. dorsi area and lean meat yield. There was no effect (P>0.05) of treatment on marbling score. Overall, the results of this study indicate that replacement of barley grain by CDC SO-I oat in finishing diets decreases DMI and as a result leads to reduced ADG, increased days on feed and lower slaughter and carcass weights.