Snakeweeds (broom, Gutierrezia sarothrae (Pursh) Britt & Rusby); and threadleaf, G. microcephala (DC.) Gray) fall into that class of poisonous weeds that seldom cause direct livestock losses because they are highly unpalatable and animals rarely consume large quantities of plant material. However, when snakeweed becomes dominant on rangeland and retards growth of desirable forage, then indirectly it becomes a serious hazard to animal health. Confined and rangelend feeding trials conducted at New Mexico State University with cattle and sheep have failed to elicit reproductive failure with elevated snakeweed dosages. Snakeweed was shown to impair certain reproductive functions such as pituitary reponsiveness to luteinizing hormone, and caused mild hepato-renal toxicity. Under rangeland conditions, livestock grazing in areas dominated by snakeweed reportedly have more serious problems, such as abortion. A commonality between confined feeding trials and rangeland grazing trials is that in the presence of snakeweed, animals typically display symptoms associated with a low-plane of nutrition such as lack of gain, emaciation, and occasional death. To reduce snakeweed dominance and improve range condition, management intervention such as herbicide or fire control may be necessary, Complicating the decision regarding snakeweed control is the uncertainty about treatment life and whether this relatively short-lived perennial weed might be eliminated by natural causes. Knowing the snakeweed population pattern in a given area greatly enhances management decisions. ©Society for Range Management. Abstract reproduced by permission.