Crude Protein, Crude Fiber, Tannin, and Oxalate Concentrations of 33 Astragalus Species

Plant introduction collections grown at the Western Regional Plant Introduction Station for preliminary evaluation and seed increase were evaluated for crude protein, crude fiber, tannin, oxalates, and readily detectable alkaloids. Sixty-eight Astragalus accessions representing 33 species and 1 unidentified accession had a range of 8.2 to 24.2% crude protein, 11.3 to 28.6% crude fiber, 4.2 to 10.0 mg/g tannin, and 0.15 to 1.10% oxalates. Species with more than 18% crude protein and less than 28% crude fiber (i.e., comparable to good quality alfalfa (Medicago sativa) hay) and acceptable levels of tannin and oxalate were A. canadensis, P.I. 19978 and A. siliquosus, P.I. 330696. None of the accessions tested gave a positive Dragendorff reagent color test for alkaloids. Some of the species reported are known to be selenium accumulators and/or contain toxic nitro-compounds that may be damaging to grazing animals. A. siliquosus is a species that contains nitro-compounds and will accumulate selenium.