Haying and Grazing Areas with Hemlock
There are two different species of hemlocks in Nebraska that can be toxic to both livestock and people.
September 16, 2024
by Brian Vander Ley, Bethany Johnston and Scott Fritz
There are two different species of hemlocks in Nebraska that can be toxic to both livestock and people. Here are some considerations as you plan to graze or hay areas with either of these two species.
Poison hemlock and spotted water hemlock
Two hemlock species are present in Nebraska: poison hemlock (Conium maculatum L.) and spotted water hemlock (Cicuta maculata). Poison hemlock is an introduced biennial that tends to grow on higher ground and has leaves like a carrot (fern-like). In early August, poison hemlock has completed its growth cycle, as it is mostly seeded out and dead. Water hemlock is a native perennial that prefers to grow in wet areas like ditches and subirrigated meadows. Water hemlock has serrated leaves (like a steak knife).
Both species can be highly toxic to both livestock and to people. Because the level of toxins is variable between individual plants, one plant may contain enough toxins to kill several animals, while another plant in the same field may be virtually risk-free when consumed. Unfortunately, there is no visible way to detect which plants are highly toxic and which are safe.
Effects of hemlock on cattle
Poison hemlock contains a group of toxins (piperidine alkaloids); whereas, water hemlock has a single, highly potent toxin called cicutoxin. Cicutoxin is one of the most potent plant toxins known. After ingestion, both plants will cause nervousness, excessive salivation, frequent urination and defecation, dilated pupils and rapid heartbeat. Intoxication with poison hemlock eventually results in respiratory paralysis, causing affected animals to become comatose and die because of suffocation. Water hemlock poisoning causes massive seizures that damage the brain of intoxicated animals, resulting in death. While both poisonings progress rapidly, animals can die within 15 minutes of ingesting a fatal dose of water hemlock and within three hours of ingesting a fatal dose of poison hemlock. Due to the rapid progression, clinical signs are not often seen, and animals are just found dead.
The greatest risk to livestock from poison hemlock is likely small exposures over time. The toxic alkaloids are similar to the alkaloids in lupine that cause crooked calf disease. The alkaloids in poison hemlock have been demonstrated to cause birth defects in feeding trials if consumed between days 40 and 100 of gestation in cattle.
Spotted water hemlock poisoning causes massive seizures that damage the brain of intoxicated animals, resulting in death in as little as 15 minutes.
The greatest risk to livestock from poison hemlock is likely small exposures over time. The alkaloids in poison hemlock have been demonstrated to cause birth defects
While both poisonings progress rapidly, animals can die within 15 minutes of ingesting a fatal dose of water hemlock and within three hours of ingesting a fatal dose of poison hemlock.
How much hemlock does it take to kill cattle?
The fatal toxic dose of water hemlock can be as small as 3.5 ounces (oz.; 100 grams) of green leaves, stems, immature seedheads, or tubers. The fatal toxic dose of poison hemlock is slightly higher, but still requires less than a pound to cause death in mature cattle.
Both kinds of hemlock are not considered highly palatable to livestock and are typically avoided. Notable exceptions to this are in overgrazed pastures with limited forage and in stored forages that are fed later, especially if the forage is processed to limit sorting. Pastures or meadows containing hemlock that are hayed will make avoiding hemlock more difficult for animals, especially if the hay has been processed or ground. A published case of water hemlock poisoning described tubers being trampled in shallow water followed by cattle drinking the water and dying.
Controlling hemlock
Controlling poison hemlock can be done by either physical or chemical methods. Physical removal of plants can be effective if steady effort is applied over time. Personal protective equipment (PPE) should be used, as hemlock is also poisonous for humans through skin contact or ingestion.
Some herbicide use can make toxic plants more palatable to animals.
For larger infestations, try chemical control using a broadleaf herbicide. 2,4-D plus dicamba is an example and spraying in the spring and fall is most effective. Water hemlock can also be controlled through similar physical and chemical methods. Note that some herbicide use can make toxic plants more palatable to animals. Since water hemlock grows near water sources, herbicides will need to be labeled for use in water areas and should be applied with caution. Read the herbicide label.
If physical removal is used, DO NOT BURN the plants. The smoke from burning hemlock is highly toxic to humans if inhaled.
If you have grazing land that contains hemlock of either kind, strongly consider eradicating these plants or fencing livestock out of patches until the hemlock can be killed and removed. Avoid incorporating hemlock into hay bales. If you suspect that hemlock may be incorporated into hay you plan to feed, strongly consider feeding it unprocessed and in sufficient quantity to allow livestock to sort out the less palatable hemlock. However, animals may still be at risk for poisoning, if the hemlock is consumed by the animal.
There are several resources to help you identify poison or water hemlock, but there are other benign plants that look similar. Nebraska Plants Toxic to Livestock (EC3037) provides pictures and information about both hemlocks.
Editor’s note: Brian Vander Ley is a veterinary epidemiologist with Great Plains Veterinary Education Center. Bethany Johnston is an extension educator with Nebraska Extension. Scott Fritz is a veterinarian and clinical assistant professor of Toxicology with Kansas State University [Lead photo by Bethany Johnston.]
Angus Beef Bulletin EXTRA, Vol. 16, No. 9-B
Topics: Health , Pasture and Forage
Publication: Angus Beef Bulletin
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