Technical Abstract: Switchgrass (Panicum virgatum L.) cultivars with improved forage quality would fill a forage gap during summer when hot dry weather reduces production of cool-season forages on marginal lands of the Northeastern USA. In this study, we used feeding trials with sheep to determine the forage quality of ‘Cave-in-Rock’, ‘Trailblazer’, ‘Shawnee’, and ‘Pathfinder’ switchgrass hays. Forage was harvested and baled as hay from field plots at Rock Springs, PA on 29 June 2007, 16 June 2008 (Cut1), and 8 August 2008 (Cut 2). In 2008, Trailblazer was unavailable so Pathfinder was substituted. Morphological development stage and leaf and stem proportions were determined at each harvest. The hays were fed to mature sheep and the digestibility and intake of dry matter (DM) and fiber fractions measured. In 2007, cultivars did not differ in digestion of DM or fiber constituents and sheep consumed switchgrass hays similarly. In 2008, sheep consumed hay of switchgrass cultivars similarly but consumed more of Cut 1 than Cut 2 hay. Cut 1 hay also had greater neutral detergent fiber (NDF) and hemicellulose digestibility than Cut 2 hay. Shawnee consistently had lower DM, fiber, and crude protein (CP) digestibility than Pathfinder in both cuts. Switchgrass cultivars selected for improved DM digestion in vitro did not have greater DM or fiber digestion compared with standard cultivars when fed to sheep. Differences among cultivars in nutritive value and in vivo fiber and DM digestion mostly were due to differences in plant maturity and leaf-to-stem ratio.