This study aimed to evaluate the ruminal degradation and intestinal digestion of nutrients of two cultivars of oat grains (CDC Nasser and CDC Seabiscuit) in comparison with a barley grain (CDC Meredith that was considered the control treatment) in dairy cows. Nasser showed higher rumen undegradable protein (RUP; P < 0.01) and intestinal digestible protein (P < 0.01) than Seabiscuit or control. However, the total digestible protein was not different among grain varieties (P = 0.25). The in vitro intestinal digestibility of RUP (dIBP) for Nasser was higher than control (P = 0.02); however, the dIBP in Seabiscuit did not differ from other cultivars. The intestinal digestible rumen bypass starch and total digestible starch were lower in the oat grain varieties than in the control (P < 0.01). The truly absorbed protein supplied to the small intestine (DVE) was highest for control, intermediate for Seabiscuit, and lowest for Nasser (P < 0.01). Moreover, control showed a higher estimated feed milk value than oat varieties (P < 0.01). In conclusion, Seabiscuit shared similar rumen degradation and intestinal digestibility with control suggesting that Seabiscuit oat grain could in some extension replace barley grain in diets for dairy cows.