Cup plant (Silphium perfoliatum Sp.) is characterized by high biomass yields and the ability to grow on marginal lands where common dairy forage sources are unable to thrive. The objective of this research was to assess its feeding value for dairy cows by comparative evaluations of DM degradability in vitro and in situ, and lactational performance in vivo when fed in partial replacement (13% of ration DM) of corn and alfalfa silages. In vitro results showed that cup plant silage only had lower DMD than the alfalfa silages, and lower pH than corn silage. In situ results showed a smaller DMD than corn and alfalfa silages, also smaller soluble and potentially degradable fractions. Lactational results showed decreased DMI and milk protein percentage, also cows sorted more against long particles. Altogether, cup plant inclusion showed no adverse health effects, sustained high milk yields, and warrants further research of its inclusion in dairy rations. OMAFRA