Location: Poisonous Plant ResearchTitle: The effect of alkaloid composition of larkspur (Delphinium) species on the intoxication of Angus heifers
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2019
Publication Date: 2/17/2019
Citation: Green, B.T., Gardner, D.R., Pfister, J.A., Welch, K.D., Bennett, G.L., Cook, D. 2019. The effect of alkaloid composition of larkspur (Delphinium) species on the intoxication of Angus heifers. Journal of Animal Science. 97(3):1415-1423. https://doi.org/10.1093/jas/skz004.
Interpretive Summary: We hypothesized Angus heifer poisoning by toxic larkspur are dependent on alkaloid ratios and total alkaloid concentrations. Results from this work suggest that larkspur containing large concentrations of alkaloids are a significant risk to cattle and that total alkaloid concentrations in combination with alkaloid ratios can be used together to accurately predict risk of larkspur poisoning to grazing cattle. Finally, for a most precise estimate of risk to cattle, in addition to chemical analysis, larkspur populations must be dosed to cattle in a laboratory setting.
Technical Abstract: Cattle losses from larkspur (Delphinium spp.) toxicity are a long-term challenge on the rangelands of western North America. In addition to animal factors that affectlivestock poisonings, plant alkaloid composition (chemotype) affects the intoxication of cattle because some chemotypes are significantly more toxic. Differences in larkspur chemotype toxicity are due to the ratios of N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids to non-MSAL-type alkaloids and the concentrations of those alkaloids in the plant material. The objective of this study was to compare the responses of 6 Angus heifers to 6 chemotypes of larkspur using a Latin square study design. These Angus heifers from the USDA-ARS, Meat Animal Research Center in Clay Center, NE, were chosen for this research because they are the most larkspur-susceptible cattle observed to date. The 6 heifers were given an oral dose of dried ground larkspur and tested for muscle weakness with an exercise test (i.e., walk time). The 6 chemotypes of larkspur had non-MSAL to MSAL-type alkaloid ratios ranging from 1.4:1 to 6:1 and were administered at an oral dose of 7.5 mg/kg MSAL-type alkaloids BW. There was a treatment effect due to larkspur chemotype (P < 0.0001), and period effects were not significant (P = 0.6). There were also significant correlations between the length of time walking on a dirt track at 5 to 6 km/h, and total alkaloid dose (r = -0.92, P = 0.0045) and alkaloid ratio (r = -0.81, P = 0.0258). Serum alkaloid concentrations at 24 h after dosing were representative of the relative abundance of the alkaloid in the plant material. Results from this work suggest that total alkaloid concentrations in combination with alkaloid ratios can be used together to accurately predict the plant risk component of larkspur poisoning to grazing cattle. Animal factors such as cattle age, breed, and sex must also be considered to comprehensively manage larkspur risk.