The acute toxicity of water hemlock (Cicuta douglasii) in a goat model

Authors: Welch, Kevin; Stonecipher, Clinton - Clint; Lee, Stephen; Cook, Daniel

Submitted to: Toxicon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2020
Publication Date: 3/1/2020
Citation: Welch, K.D., Stonecipher, C.A., Lee, S.T., Cook, D. 2020. The acute toxicity of water hemlock (Cicuta douglasii) in a goat model. Toxicon. 176:55-58. https://doi.org/10.1016/j.toxicon.2020.02.010.
DOI: https://doi.org/10.1016/j.toxicon.2020.02.010

Interpretive Summary: Water hemlock plants are in the genus Cicuta in the Apiaceae family (formerly Umbelliferae) and comprise four different species. The two predominant species in the Great Basin region of the western United States are C. maculata and C. douglasii. Water hemlock plants are found in wet areas including small stream beds, river banks or marshy areas. Water hemlock is toxic to all species of livestock. Additionally, there are a number of reports of humans mistaking water hemlock for wild parsnip and becoming severely poisoned. The toxic components in water hemlock are C17 polyacetylenes, with cicutoxin being the most studied. The tubers contain the highest concentration of cicutoxin, with little cicutoxin found in the above ground parts. The tubers are reported to be the most toxic plant part, with a report of death losses occurring from cattle eating green seeds. The stems and leaves are thought to be relatively nontoxic, as there is considerable evidence in the field that animals graze the plants during the vegetative stage without any adverse effects. However, there is some question as to how much plant an animal can eat before severe/lethal effects occur. Therefore, the objective of this study was to determine the lethal dose of water hemlock tubers in a goat model. Additionally, we compared the toxicity of tubers versus the above ground parts, including green seeds. The data presented in this study suggest that goats can be used as a small ruminant model to study the toxicity of water hemlock. There was a dose-response relationship for the toxicity of the tubers, including time to onset of clinical signs. Based upon the plant material and size of goats used in this study, consumption of 1-2 small tubers, or 1 larger tuber, during the green seed phenological stage is enough to kill a goat. Although cattle are much larger than goats, they are also potentially more susceptible than goats, and thus there may not be linear extrapolation to determine a lethal dose of tubers to cattle. In this study, we also demonstrate that the toxins from water hemlock can be identified in the rumen of poisoned animals, and thus chemical analysis of rumen contents can be used to aid in the determination of the cause of death of animals poisoned in a field setting. Finally, proper herd management practices should be used to limit the exposure of livestock to areas with water hemlock due to the rapid and potentially lethal outcome.

Technical Abstract: Water hemlock (Cicuta douglasii) is one of the most toxic plants to livestock and humans. Little is known regarding the amount of plant required to cause death. The objective of this study was to determine a lethal dose of water hemlock in a goat model. Plants were dosed to goats via oral gavage of freeze-dried ground plant material. The results from this study suggest that 1-2 fresh tubers would be lethal to goats.