Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 4, 2011
Publication Date: May 1, 2011
Citation: Cook, D., Green, B.T., Welch, K.D., Gardner, D.R., Pfister, J.A., Panter, K.E. 2011. Comparison of the toxic effects of two duncecap larkspur (Delphinium occidentale) chemotypes in mice and cattle. American Journal of Veterinary Research. 72(5):706-14. Interpretive Summary: Larkspurs (Delphinium spp.) are poisonous plants found on rangelands in Western North America. Larkspur’s toxicity has been attributed to the norditerpenoid alkaloids which are divided into two main structural groups; the highly toxic (N-methylsuccinimido) anthranoyllycoctonine type (MSAL-type) and the less toxic 7,8-methylenedioxylycoctonine type (MDL-type). Plants high in the MSAL-type alkaloids are thought to be the most toxic to cattle and the concentrations of these alkaloids have been used as a predictor of plant toxicity. Duncecap larkspur, Delphinium occidentale, occurs throughout much of the Intermountain West and Northwestern United States. D. occidentale has two chemotypes one containing the MSAL-type alkaloids and one lacking the MSAL-type alkaloids; both of which are unique in their geographical distribution. To determine toxic potential, the relative toxicity of each chemotype was evaluated in mice and cattle. The results from this study indicate that the two chemotypes are different in their toxic potential in both mice and cattle. These findings have important implications in grazing management decisions on D. occidentale-infested rangelands and they demonstrate that botanical classification alone is not a good indicator to determine the toxic risk of D. occidentale.
Technical Abstract: Objective-This study tested the hypothesis that a Delphinium occidentale chemotype containing the MSAL-type alkaloids is more toxic than a D. occidentale chemotype lacking the MSAL-type alkaloids in mice and cattle. Animals-240 male Swiss Webster mice and 11 black Angus steers Procedures-Total alkaloid extracts from eight plant collections were administered by tail vein injection to male Swiss Webster mice. Dried, finely ground larkspur was administered to steers by oral gavage in a range of doses equivalent to 37.6-150.4 mg/kg body weight of total alkaloids. The steers were monitored for heart rate at time zero and 24 hours. The steers were exercised as a measure of muscle weakness. Results-Alkaloid extracts prepared from plant populations containing the MSAL-type alkaloids had an average LD50 in mice of 2.3 mg/kg BW versus 54.2 mg/ kg BW from extracts prepared from plant populations lacking the MSAL-type alkaloids. A similar trend was observed in cattle as the steers responded differentially in terms of heart rate and muscle weakness to larkspur due to the presence or absence of the MSAL-type alkaloids. Conclusions and Clinical Relevance-D. occidentale containing the MSAL-type alkaloids poses a distinct quantifiable risk of being toxic to livestock. Alternatively, D. occidentale containing only the MDL-type alkaloids is much less toxic, and the corresponding risk to grazing livestock appears to be lower. Further research in cattle will be necessary in order to refine grazing management recommendations when larkspur with these chemotypes is present on rangelands.