Springtime is the season of renewal, with green pastures and frolicking calves. But, spring can also be deadly to your cattle if poisonous plants are present in your pastures.

Many poisonous plants emerge in the early spring before grasses begin to grow, explains Kip Panter, research leader at USDA’s Poisonous Plant Research Lab in Logan, UT. “During cool, wet springs, poisonous plants often gain an advantage over the grasses and if livestock are turned out too early poisoning may occur,” he says. This is especially true for low larkspur, lupines, water hemlock and poison hemlock.

Larkspurs – Low larkspur is short-lived and high risk in early spring; once seeds have shattered, however, very little risk from low larkspur remains. Tall larkspurs are often high risk in early to mid summer when the flower/seed heads are prevalent. Storm episodes often drive cattle into areas where tall larkspur is prevalent and large cattle losses may result.

Tall larkspurs tend to grow at higher elevations on deep soils where a plentiful supply of moisture is available. They grow in mountain meadows on sites where deep snowdrifts persist well into the growing season, under aspens on north-facing slopes, along streams, or around seeps and springs. Tall larkspur begins growing as soon as the snow melts, but at the upper limits of their distribution this may not occur until July.

Low larkspurs tend to grow at lower elevations where they mature and become dormant before the soil moisture is depleted. They begin growing in early spring, often before other forage begins growth. Low larkspurs grow best when springs are cold and wet. Cattle will graze low larkspur at all stages of growth, but most often graze it after flowering.

Plains larkspur is found primarily on the high plains of Colorado and Wyoming. It begins growth in spring before other plants.

Lupines – The greatest risk of lupine is “crooked calf syndrome,” caused by pregnant cows or heifers grazing certain lupines during late first trimester or early second trimester. The species of lupine and the alkaloid profile is required to evaluate risk. Cows may give birth to calves with cleft palate and skeletal defects if the cows ingest certain lupines during early gestation (crooked calf syndrome) – the 40th to the 100th day of gestation.


Poisonous species of lupine are toxic from the time they start growth in spring until they dry up in fall. Younger plants are more toxic than older plants; however, plants in the seed stage in late summer are especially toxic because of the high alkaloid content of the seeds. Lupines are legumes and are relatively high in protein, especially the seed pods, and may become a preferred forage species when grasses become mature and dry. Under proper conditions, some lupines make good forage.

Lupines grow on foothills and mountain ranges in sagebrush and aspen areas. Lupine populations expand during wet seasons and may die back during dry seasons. The seed reserve in the soil remains high; when environmental conditions are optimum, lupine population will increase.

Poison hemlock – Poison hemlock grows throughout the U.S. and is sometimes confused with western water hemlock – a more deadly plant – because the names are similar. Poison hemlock has a number of common names, including deadly hemlock, poison parsley, spotted hemlock, European hemlock, and California or Nebraska fern.

All parts of poison hemlock – leaves, stem, fruit, and root – are poisonous. Leaves are especially poisonous in spring, up until the plant flowers. Fresh leaves are unpalatable, so livestock seldom eat hemlock when other feed is available.

Poison hemlock is found at roadsides, along fences and ditch banks, on edges of cultivated fields, along creekbeds and irrigation ditches, and in waste areas. It also may invade fields or pastures.

Western water hemlock—Water hemlock is the most violently toxic plant that grows in North America. Only a small amount of the toxic substance in the plant is needed to poison livestock or humans. The toxin acts on the central nervous system and is a violent convulsant.

Water hemlock may be confused with poison hemlock because of their similar flowers. However, these are different plants and cause different types of poisoning. The underground portions of the plant, especially the tuberous roots, are very toxic. People are sometimes poisoned by eating the roots, which they mistake for wild parsnip.

Cattle have been known to eat lethal amounts of water hemlock in pastures having adequate forage; therefore, animals should be prevented from grazing water hemlock-infested areas. Animals have been poisoned by eating roots that have been brought to the surface by plowing or cleaning ditches.

For additional information, go to www.pprl.usda.gov. For complete information on the poisonous plants mentioned here, click here.