Recent work suggests several European‐ and Mediterranean‐derived cultivars of birdsfoot trefoil (BFT, Lotus corniculatus L.) are well adapted to the colder continental United States and produce forage with greater condensed tannin (CT) concentrations, but comparable neutral detergent fiber (NDF) and slightly lower crude‐protein (CP) concentrations than the commonly grown cultivar Norcen. In the current study, thirteen of these foreign‐derived cultivars and Norcen were harvested under two‐ or three‐cut management during 2006 in Michigan, Utah, Wisconsin, and West Virginia and analyzed in vitro for rumen degradable and undegradable protein on a CP and dry‐matter (DM) basis (RDPCP, RDPDM, and RUPDM) and for rumen degradable and true degradable DM (RDDM and TDDM). Foreign‐derived cultivars usually produced forage with greater RUPDM and lower RDPCP, RDPDM, RDDM, and TDDM than Norcen. The low NDF cultivar Bokor uniquely combined high CT and RUPDM with high TDDM. The highest yielding cultivar Lotar also produced herbage with moderate to high CT, RUPDM, and TDDM. Concentrations of CT and CP influenced RDPCP, RDPDM, and RDDM, while CT affected RUPDM, and fiber components influenced TDDM; relationships were greatly influenced by growth environment. Reductions in RDPDM exceeded gains in RUPDM as CT increased, thus, feeding of high‐CT cultivars could mainly curb urinary N excretion from excess RDPDM rather than boost amino acid supply from potentially digestible RUPDM. Additional work is needed to improve the nutritional consistency of harvested BFT across environments and to develop higher‐yielding cultivars with optimal RDPDM and RUPDM and high TDDM for maximizing livestock performance.