Technical Abstract: Many forages and associated plants have secondary compounds that can be toxic if consumed in sufficient quantities. Historically, poisonous plants have been significant impediments to livestock production on rangelands, and to a lesser degree on pastures. The mission of the USDA/ARS Poisonous Plant Research Lab is to identify plants that are poisonous to livestock, determine the toxin and its effects on livestock, describe the conditions under which animals graze these plants and intoxication occurs, and develop recommendations and management strategies to reduce the risk of poisoning. Research at the Lab has produced management strategies to reduce the risk of poisoning in the following plants. Halogeton poisoning can be prevented by preconditioning animals to oxalate containing plants, or preventing hungry animals from grazing dense patches of halogeton. Veratrum and Lupine cause birth defects when the dam eats them at certain stages of fetal development. Prevent access to these plants during the susceptible period of gestation and when the teratogen level is high. Locoweed populations fluctuate with the changing climatic conditions, increasing in wet years and dying back in drought. Locoweeds are often relatively more palatable than associated forages at certain times of the year, and losses can be prevented by denying access to locoweed-infested sites during these critical periods. Tall larkspur is acutely toxic and palatable to cattle on mountain summer rangeland. A management strategy has been proposed to graze early in the season when larkspur is unpalatable, remove cattle during the high risk period during flowering when the toxin level is still relatively high and cattle begin eating the plant, then grazing it late in the season beyond the pod stage when toxicity is low. Needles from Ponderosa pine and several other conifers cause late term abortions in cattle. Cold temperatures and deep snow influence cattle to eat pine needles. Losses can be prevented by denying access to the needles during the last trimester of gestation. ELISA immunologic assays are being developed for larkspur, locoweed, pine needles and pyrrolizidine alkaloids. They will be used as diagnostic tools, and vaccines may be