Any weed or undesirable plant that grows in pastures where cattle graze, or a plant toxic to cattle.
Compound of 'cow' and 'weed' (Old English 'weod'). The term applies to various plants that plagued farmers by competing with forage crops or poisoning livestock.
Some 'cowweeds' like locoweed actually cause cattle to act drunk or neurotic from alkaloid toxins—pioneers reported entire herds behaving bizarrely, not realizing the plants themselves were the culprit.
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