Are plants poisoning your livestock?
May 20, 2005
There are several common plants in southwest Missouri pastures that are considered poisonous to livestock according to Eldon Cole, University of Missouri Extension livestock specialist. The good news is that these poisonous plants rarely result in deaths.

Key characteristics of the vegetative hemlock plants are their hairless and purple-spotted, hollow stems. Their leaves are pinnately compound and arranged alternately and hairless. Their flowers are white and produced in compound umbels.

“One such plant is hemlock, a biennial that is tall growing, purple-spotted and hollow stemmed. Locally it’s often called wild carrot. It’s probably already four to six feet tall and begins its spring growth in February or early March,” said Cole.

This spring a veterinarian told Cole he had seen his first incident of hemlock poisoning. In this case, four or five Holstein heifer calves (weighing in 400 to 500 pounds) were showing classic hemlock poisoning symptoms: salivation, diarrhea, nervousness, trembling, convulsions and coma. Post-mortem examination by the veterinarian confirmed the diagnosis. The heifers had large quantities of hemlock in their rumen.

According to Cole, the poisonous plant concern usually results when the only green vegetation for them to eat is poison, as was the case with the hemlock and the Holsteins. “It usually takes more than just a bite or two of most toxic plants to cause problems. Livestock seem to have a sixth sense that steers them away from even attempting to graze toxic plants like hemlock, nightshade, buttercup, cocklebur, pokeweed and wooly croton. Some limited research with other species hints that the ability to avoid poisonous plants could be learned by grazing with their mothers.

Don't feed your neighbor's livestock Japanese yew

According to Cole, every year the most animal deaths from a toxic plant are caused by the ornamental shrub Japanese yew. “It’s not too uncommon to hear of some well-meaning person trimming their yews and throwing the clippings over the fence to cattle, sheep or goats. In those cases, death is almost guaranteed,” Cole said.

A complete list of weeds of field crops and pastures may be found here. The University of Missouri Guide Sheet G4970, “Plants Poisonous to Livestock” is available at extension centers or go here.

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