Haying and Cattle Grazing Areas with Hemlock
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There are two different species of hemlocks in Nebraska that can be toxic to both livestock and people. Here is some information that is important for you to consider as you plan grazing or haying in areas with either of these two species of hemlock.
About 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 sub-irrigated meadows. Water hemlock has serrated leaves (like a steak knife). Both of these 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 or safe.
Spotted water hemlock is a perennial, that grows in wet areas, like ditches and subirrigated meadows. The leaves are serrated. Photos by Bethany Johnston, Nebraska Extension educator.
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 cause massive seizures that damages 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 3 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 40-100 of gestation in cattle.
How much hemlock does it take to kill cattle?
The fatal toxic dose of water hemlock can be as small as 3.5 oz (100 grams) of green leaves, stems, immature seed heads, 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 is 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. 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. It is worthwhile to 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 done 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, as there are other benign plants that look similar. “Nebraska Plants Toxic to Livestock (EC3037)” provides pictures and information about both hemlocks.
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