University of Missouri-Columbia Several species of plants poisonous to livestock are distributed throughout Missouri, and many of them are commonly found in native or improved pastures. This guide describes some of the more common species that are toxic to various livestock. A common characteristic of several poisonous plants is a disagreeable taste that ordinarily discourages livestock from grazing them.
Some species are poisonous only during certain stages of growth.
For example, common cocklebur is most poisonous shortly before reaching the two-leaf stage. During this period of growth, cocklebur is exceedingly toxic to pigs but can also harm cattle and sheep. If livestock poisoning is suspected, carefully examine the grazing area for poisonous plants. Species commonly found in shady areas include white snakeroot, bracken fern, pokeweed and buckeye. Moist areas along creeks or ditch banks are favorable for growth of water and poison hemlock, black nightshade and horsetail.