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Poisonous plants are a major production cost to beef producers in western North America.  Tall larkspur (Delphinium occidentale) is considered one of the most important poisonous plants to beef cattle production as death losses can reach 15% in pastures where larkspur is present.  No practical approach to combating larkspur toxicity exists except removing the plant with herbicides, or restricting livestock use of pastures until toxin levels have diminished.  Although native ruminants forage on ranges with tall larkspur present it is not known if these animals can metabolize the toxins found in larkspur.  To better understand potential pathways of toxin metabolism, we evaluated microbial metabolism of the tall larkspur toxin methyllycaconitine (MLA) by incubating tall larkspur extract in rumen fluid and quantifying the change in MLA concentration after 48 hrs.  Samples of rumen fluid from five different species were used in this study including elk, bison, white-tailed deer, cattle, and domestic goats.  While white-tailed deer had the least residual MLA present after incubation (84.33% remaining), most wild species demonstrated a decrease in MLA over the 48 hour incubation.  These data suggest that wild ruminants may exhibit microbial-mediated degradation of MLA.  Although further research is needed to improve our understanding of these dynamics, this initial study hints at the potential to isolate microbes capable of degrading a toxin responsible for livestock casualties.