Alkaloid-containing plants exact a heavy economic toll on livestock produc-tion in rangelands of western North America. Losses to these plants can be reduced or eliminated by recognizing plants containing alkaloids, understand-ing when livestock graze specific toxic plants, and knowing signs of potential toxicity. Grazing schemes can then be developed based on knowledge of the temporal and spatial dynamics of alkaloid concentration and consumption by livestock.Lossescanbereducedbyensuringthatlivestockarenotexposedorhave limitedexposureduringperiodsofgreatestrisk(i.e.,highesttoxinconcentration)or whenlivestockaremostlikelytoeattoxicplantsinsufficientamountstoproduce toxicity.

Death camas (Zigadenus spp.) grows on foothill ranges in much of the Rocky Mountain area. Animals eating death camas die from reduced blood pressure and heart failure. Death camas is one of the first plants available during spring, and animals may graze the plant if other forage is lacking. Generally, recognizing the presence of death camas and understanding the acutely toxic nature of the plant will aid in avoiding problems. Hungry animals should not bedriventhroughadeathcamas-infestedpasture.Sheepinparticularshouldnotbe beddednearlargepatchesofdeathcamas,andsheepherdersshouldavoidstressing sheep by rapidly driving them if they do eat death camas. Death camas can be controlledbyphenoxyherbicides.

False hellebore (Veratrum spp.) is f ound in moist habitats in the Pacific Northwest and Rocky Mountain states. It is grazed by sheep and goats and causes birth defects (i.e., monkey-faced lambs). Livestock management to avoid losses t o false hellebore i s r elatively simple because the window of toxicity when false hellebore poisons t he fetus i s r elatively narr ow (i.e., 14 to 33 days gestation). Pregnant animals, particularly sheep, should not be allowed access t o veratrum-infested pastures during this period. Cattle rarely ea t the plant, therefore no special management is needed. For sheep, false hellebore i s quite palatable, and herders must keep bred sheep from ingesting false hellebore f or about one month after the rams are removed. This is not difficult to accomplish because false hellebore is limited in distribution to moist mountain habitats and grows in easy to identify dense patches. Although effective herbicidal control is available, it may not be practical because the major populations grow in

Poison hemlock (Conium maculatum) grows throughout the United States in areas with abundant moisture (i.e., creeks, ditches etc.). Animals eating poison hemlock die from acute respiratory failure or have deformed offspring. The most critical season to avoid poison hemlock is spring because the plant often appears before other forage has emerged. Green seed pods may be eaten in mid-to-late summer. Furthermore, poison hemlock may regrow in fall after seeds shatter. Ingestion during fall may coincide with birth defects in pregnant cattle, if they are i n the firs t trimester of gestation (days 30-75). If poison hemlock invades hay fields, the contaminated hay can poison livestock. Even though toxicity decreases upon drying, sufficient toxins may be r etained to poison livestock. Cattle appear to be particularly susceptible because of their acceptance of the plant and their sensitivity to the alkaloids t hat c ause birth defects. Poison hemlock can be easily controlled with phenoxy herbicides.

Acute t oxicity problems are l es s common now, but lar ge sheep losses occurred frequently 100 years ago. Deaths occ ur when livestock, usually sheep, ingest a large amount of seed pods in a short time. This can occur from contaminated hay or from hungry animals gaining access t o lupine-dominated forage, and can be prevented by using lupine-free hay and avoiding lupine-dominated ranges when other forage is scarce. During some years, lupine populations may temporarily increase on rangelands not normally problematic. Livestock producers need to be aware of lupine populations and be sufficiently alert to alter grazing or breeding programs when these eruptions occur. Lupine populations increased dramatically during 1997 in Washington, Oregon, Idaho, and Montana, causing severe l osses. For example, producers in Adams County, Washington lost over 30% of their calves ( >4000 calves) from lupine- caused birth defects.

38of rotational grazing scheme. Herbicidal control of lupines is feasible, but is usually more expensive than altering a grazing management program.

Lupines (Lupinus spp.) are widely distributed throughout the western U.S. Cattle eating lupine may have deformed or "crooked" calves, and sheep may be poisoned outright by lupine. Livestock losses from lupine poisoning can largely be prevented by understanding two interrelated aspects. First, the highest concentrations of toxic alkaloids tend to occur in immature lupine plants and seed pods. Second, pregnant cattle are susceptible to the effects of alkaloids that cause birth defects during a window from 40 to 70 days of gestation, occasionally extending to 100 days. Birth defects in cattle can be prevented by using breeding or grazing programs that avoid placing pregnant cattle in lupine-dominated pastures in the first trimester of gestation. Alternatively, risk can be reduced by allowing only short-term access to lupines by pregnant cattle in some form