ARS | Publication request: Effect of MDL-type alkaloids on tall larkspur toxicosis

Submitted to: Poisoning by Plants, Mycotoxins, and Related Toxins
Publication Type: Book / Chapter
Publication Acceptance Date: February 1, 2011
Publication Date: May 2, 2011
Citation: Welch, K.D., Gardner, D.R., Panter, K.E., Green, B.T., Cook, D., Pfister, J.A., Stegelmeier, B.L., Davis, T.Z. 2011. Effect of MDL-type alkaloids on tall larkspur toxicosis. In: Riet-Correa, F., Pfister, J., Schild, A.L., Wierenga, T., editors. Poisoning by Plants, Mycotoxins, and Related Toxins. Cambridge, MA: CAB International. 94:540-9. DOI: 10.1079/9781845938338.0540.

Interpretive Summary: Current management recommendations for grazing cattle on larkspur-infested ranges are based primarily on the concentration of MSAL-type alkaloids. Delphinium barbeyi is one of the more problematic species of tall larkspur plants due to its high concentration of MLA. However, the most abundant norditerpenoid alkaloids in most D. barbeyi populations are the less toxic MDL-type alkaloids, either deltaline or 14-OAD. Previous research using a mouse model, demonstrated that the MDL-type alkaloids have an additive affect on the toxicity of MLA. In this study, experiments were performed to determine if MDL-type alkaloids affect the overall toxicity of tall larkspur plants in cattle. The research from this study demonstrates that MSAL-type alkaloids such as MLA cause greater toxicity than MDL-type alkaloids and are the primary factors responsible for the toxicity of larkspur plants. Consequently, for a larkspur plant to be toxic to livestock, a sufficient quantity of MSAL-type alkaloids is required. However, MDL-type alkaloids appear to potentiate the overall toxicity of the MSAL-type alkaloids and should be considered when predicting potential toxicity of larkspur populations. Consequently 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

Technical Abstract: Larkspur plants contain numerous norditerpenoid alkaloids which include the 7, 8-methylenedioxylycoctonine (MDL) -type alkaloids and the N-(methylsuccinimido) anthranoyllycoctonine (MSAL) -type alkaloids. The MSAL-type alkaloids are generally much more toxic (typically > 20x). Toxicity of many tall larkspurs has been attributed to their high concentration of MSAL-type alkaloids including methyllycaconitine (MLA). However, the less toxic MDL-type alkaloids are found in the highest concentrations in most Delphinium barbeyi and Delphinium occidentale populations. Previous work by our laboratory demonstrated that MDL-type alkaloids increase the acute toxicity of MLA in mice. In this study, cattle were dosed with different populations of tall larkspur that contain different ratios of MDL- to MSAL-type alkaloids. Three different populations of tall larkspur were used, a D. barbeyi population from the Manti, Utah area with a ratio of 3.1:1.0 MDL- to MSAL-type alkaloids, another D. barbeyi population from the Cedar City, Utah area with a 1:1 ratio, and a D. glaucescens population from the Dillon, Montana area with a 0.6:1.0 ratio. The dose, based on the MSAL-type alkaloid concentration, required for each plant population to elicit similar clinical signs of poisoning in cattle was determined. As the ratio of MDL- to MSAL-type alkaloids in the plant material decreased, the amount of MSAL-type alkaloids required to elicit clinical signs increased approximately 2 fold. The results from this study indicate that less toxic MDL-type alkaloids in tall larkspur exacerbate the toxicity of the plant in cattle. 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.