Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2011
Publication Date: 7/1/2012
Citation: Welch, K.D., Green, B.T., Gardner, D.R., Cook, D., Pfister, J.A., Panter, K.E. 2012. The effect of 7,8-methylenedioxylycoctonine-type diterpenoid alkaloids on the toxicity of tall larkspur (Delphinium spp.) in cattle. Journal of Animal Science. 90(7): 2394-401.
Interpretive Summary: Larkspurs (Delphinium spp.) are one of the most serious toxic plant problems on foothill and mountain rangelands in the western U.S. The toxicity of larkspur plants is due to alkaloids which occur as 2 chemical structural types, the MDL type, such as deltaline, and the MSAL type, such as methyllycaconitine (MLA). Although the MSAL-type alkaloids are more toxic (typically >20x), the MDL-type alkaloids are generally more abundant in D. barbeyi and D. occidentale populations. Current management recommendations for grazing cattle on larkspur-infested ranges are based primarily on the concentration of the MSAL-type alkaloids. In this study, we examined the role of MDL-type alkaloids in the overall toxicity of tall larkspur plants to cattle while controlling the dose of MSAL-type alkaloids. The results from this study indicate that MDL-type alkaloids exacerbate the overall toxicity of the MSAL-type alkaloids and should be considered when predicting potential toxicity of larkspur populations. Therefore, when chemical analyses are performed on larkspur plants to assess their toxic potential, the concentration of both the MSAL-type and total alkaloids should be determined, with more weight given to the MSAL-type alkaloids. Finally, the results from this study indicate that larkspur plants containing large amounts of MDL-type alkaloids, in addition to high MSAL-type alkaloid content, should be considered potentially more dangerous to cattle than plants with only high MSAL-type alkaloids.
Technical Abstract: Delphinium spp. contain numerous norditerpenoid alkaloids which are structurally delineated as 7, 8-methylenedioxylycoctonine (MDL) and N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids. The toxicity of many tall larkspur species has been primarily attributed to their high concentration of MSAL-type alkaloids, such as methyllycaconitine (MLA), which are typically 20 times more toxic than the MDL-type alkaloids. However, the less toxic MDL-type alkaloids are often more abundant than MSAL-type alkaloids in most Delphinium barbeyi and Delphinium occidentale populations. Previous research demonstrated that MDL-type alkaloids increase the acute toxicity of MSAL-type alkaloids. In this study, cattle were dosed with plant material from two different populations of tall larkspur containing either almost exclusively MDL- or MSAL-type alkaloids. These two plant populations were combined to create mixtures with ratios of 0.3:1, 1:1, 5:1, and 10:1 MDL- to MSAL-type alkaloids. The dose that elicited similar clinical signs of poisoning in mice and cattle was determined for each mixture based on the MSAL-type alkaloid content. As the ratio of less toxic MDL- to MSAL-type alkaloids increased, the amount of MSAL-type alkaloids required to elicit clinical signs decreased. These results indicate that the less toxic MDL-type alkaloids in tall larkspur exacerbate the toxicity of the plant. Consequently, both the amount of MSAL-type alkaloids and the amount of total alkaloids should be fully characterized to more accurately determine the relative toxicity of tall larkspur plant material.