Poisonous Range and Pasture Plants
May 2012
Compared to many other states, Nebraska livestock producers are generally fortunate in having fewer poisonous plant problems. However, each year there are cases where animal death can be positively attributed to plant poisoning and others where it is suspected. A key to preventing losses from poisonous plants is identification of those plants and conditions or management practices that might increase the risk.
The naturally occurring toxic compounds that could occur in different plant species include alkaloids, hydrocyanic acid, nitrates, cicutoxin, locoine, and glycosides and resinoids. Of these, nitrates are the most commonly occurring and there are many plant species that are known to accumulate nitrates. The potential for high levels of nitrates is most often associated with the different warm-season annual forages (sudangrass, millet, sorghum-sudangrass hybrids), small grain forages, and several different weed species. The primary factors that cause excessive nitrate accumulation are plant stresses such as drought or hail and high levels of nitrogen in the soil. The high level of soil nitrogen could come from excess nitrogen fertilizer or manure as could be found in feed-grounds or corrals.
Aside from those plant species that accumulate nitrates, the following table includes some of the more common poisonous plant species found in Nebraska and the toxic compound inherent with those species.
| common poisonous plant species found in Nebraska | ||
|---|---|---|
Toxic plant species |
Where found |
Toxic compound |
| Arrowgrass | Wet meadows, marshes | Hydrocyanic acid in leaves |
| Deathcamas | Statewide, except sands | Toxic alkaloids throughout all plant parts |
| Dwarf milkweed | Central and west | Glycosides and resinoids |
| Lambert crazyweed | Central and west | Locoine throughout all plant parts |
| Larkspurs | Statewide | Toxic alkaloids throughout all plant parts |
| Nebraska lupine | Central and west, sandy | Toxic alkaloids, particularly fruit and seeds |
| Nightshades | Central and east | Toxic alkaloids |
| Poison hemlock | Statewide | Alkaloids throughout all plant parts |
| Riddell groundsel | Central and west | Alkaloids esp in young leaves |
| Showy milkweed | Statewide | Glycosides and resinoids |
| Water hemlock | Statewide | Cicutoxin, esp in roots and stalks |
| Chokecherry | Statewide | Hydrocyanic acid |
Management Practices to Reduce Poisonings
Livestock have distinct grazing behaviors and preferences for certain sites or locations within a pasture, plant species, and plant parts. The consumption of poisonous plants may often be a result of an animal 'testing' the novel plant that is available within that pasture. This can sometimes occur when animals are moved into a new pasture or when new animals are brought in and placed in a pasture that contains unfamiliar plant species.
Fortunately, with most poisonous plant species, consumption of a single bite or plant will usually not result in the quantity of toxin needed to cause animal health problems or death. More often it is when animals graze larger quantities of that toxic species. This could be because of an individual animal foraging behavior or because other forage is limited in that pasture.
It has been commonly observed that the incidence of plant poisoning increases during drought conditions or when pastures are overgrazed. Overall, important steps and management practices that producers can follow to reduce the risk of plant poisonings include:
- Become familiar with the identification of the toxic plant species that might occur in your pasture or rangeland type.
- Avoid placing livestock in areas of grazing where poisonous plants are a large part of the plant community.
- Use control measures if excessive numbers of poisonous plants are establishing themselves within a pasture.
- Time grazing to provide high levels of desirable forage and reduced toxin periods of poisonous plants.
- Always carefully evaluate the plant communities in the pasture to be used next and closely inspect feedstuffs from new sources. If in doubt - delay the move.
- Graze at stocking rates which propagate the desirable species and prevent over grazing.
- Distribute livestock effectively so that over-utilization of "easy" areas does not increase poisoning risk.
Dr. Jerry Volesky, Associate Professor of Agronomy
West Central Research & Extension Center - North Platte, North Platte, NE