Extension column: Watch for toxic plants at turnout this year | TSLN.com

Extension column: Watch for toxic plants at turnout this year

Steve Paisley
for Tri-State Livestock News

In many parts of Wyoming we have received some very beneficial and timely snows and rains beginning in mid April. Many of the pastures are greening up nicely, but have been very slow to respond probably due to the very dry summer and fall last year.

The slow forage growth, along with timely precipitation, have created a unique larkspur and death camas situation on many ranches. The grass growth is slow to develop, yet cattle are hungry for green grass and anxious to graze. Some of the early plant responders to moisture have been alkaloid-containing plants such as larkspur and death camas, creating a flush of spring growth and flowering, as well as an increased opportunity for alkaloid poisoning in western range herds. Tall larkspur (wild delphinium) is a cattle killer. Larkspur and other alkaloid plant poisonings claim average death losses of 4-5 percent annually in some allotments in Utah, Colorado, Wyoming, Idaho and Montana. The USDA-ARS station in Logan, Utah has done extensive research in alkaloid toxicities and how to manage for them. Some of their recommendations include:

Pasture Management

It goes without saying that the best preventative is prevention – trying to avoid using pastures with larkspur during seasons and situations when the plants are most deadly. Larkspur is most toxic during the early growth phases, remaining toxic during the flowering phase. The toxicity declines as the plant matures throughout the summer. However, seed pods remain very toxic, and can be a big management issue during fall and winter grazing situations. For summer grazing management, poisoning of cattle is less likely after the flowering phase has passed.

Cattle typically avoid larkspur and other alkaloids during the preflower and flowering stages. However – this year is somewhat unusual in that forage growth has been delayed, and cattle are often “hunting” for forage

Researchers say tall larkspur contains up to 20 different alkaloids that vary in toxicity from very poisonous to almost harmless. Alkaloid levels can vary from one patch to another, and from year to year in the same patch. These differences may be part of the reason for variations in annual death losses. It takes more pounds of larkspur consumption in some years to be fatal.

Cattle Management

This may be very specific to each operation. While yearling cattle would pose less of a risk in that they aren’t carrying a pregnancy, yearling cattle are often naïve to alkaloid grazing and may lead to problems. Mature cows, although consuming a larger amount of total forage, are more experienced grazers and tend to avoid noxious plants.

Additive toxicity

Additive nature of toxic low larkspur and death camas. Rangelands in the western United States contain multiple poisonous plants. A consequence of this is that one poisonous plant can exacerbate the toxicity of another poisonous plant. Two poisonous plants often found growing together are low larkspur and death camas. ARS researchers in Logan, Utah, using a mouse model, determined that there is an additive effect when alkaloids from both low larkspur and death camas are administered. This suggests that beef cattle grazing both larkspur and death camas can eat less of each plant in combination compared to consuming each plant individually.

Clinical signs and clearance rates

USDA researchers in Logan, Utah, have determined how long it takes beef cattle to clear the toxic alkaloids from their blood so that an accurate risk assessment can be made. They discovered that clinical poisoning is likely to be the most severe approximately 18 hours after eating alkaloids, and those animals should be closely monitored for at least 36 hours beyond initial exposure. Additionally, a withdrawal time of approximately seven days is required to clear over 99 percent of the toxic alkaloids from the bodies of poisoned cattle that have ingested low larkspur.

Signs of poisoning

The alkaloid compounds in larkspur and other toxic plants work by inhibiting nerve impulses at the junction of the nerves and muscles, causing muscle paralysis. Symptoms include muscle weakness, staggering gait, inability to stand, bloat (because of digestive smooth muscle paralysis) and respiratory failure. Affected animals should not be moved because of the additional stress associated with moving the animal.


Cattle that have an acute ingestion of alkaloids should be monitored closely. Attempt to keep the animals hydrated, and treat any signs or symptoms of bloat.

Animals have a wide variation in both the ability to individually handle alkaloid compounds, as well as a wide degree of ingestion/aversion to the plants, so alkaloid poisoning can seem very random. Closely monitoring herds that are exposed to alkaloid-containing plants, recognizing the symptoms, and reacting quickly can dramatically reduce losses. Contact and consult with your local veterinarian for specific treatment options as well as diagnosis.


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