Antelopehorn Milkweed

Asclepias asperula



Antelopehorn milkweed is an erect-stemmed plant growing to about 15 inches tall. Leaves are narrow, lance-shaped and about 3 inches long. The flowers are greenish with distinctive purplish horns and are present from March to October. The fruit is a wrinkled pod containing silk-tufted seeds.


Most abundant in westernTexas, this plant has also been recorded in the northern, central and east central regions of the state. It ranges north into Nebraska and west into southern Utah and southeastern California.It often abounds in open pastures, along arroyos, draws, bar ditches, trails and roadsides.

Toxic Agent

The toxic agents involved are cardiac glycosides. Antelopehorn milkweed poisons all livestock, especially sheep. A toxic dose is generally considered to be 1.2 percent of the animal's body weight in green plant material.

Signs of Livestock Ingestion

Signs of poisoning produced by most species of Asclepias differ only in degree. They include: First, profound depression, weakness and staggering; Collapse, followed by frequent, intermittent muscular tremors; Labored respiration, elevated temperature and pupil dilation; Death after a comatose period of variable duration.

Signs appear within a few hours of ingestion of a toxic dose, and death follows within a few days in most fatal cases.

Management Strategies

Animals dislike the taste of milkweeds and seldom graze them unless they are hungry and confined to milkweed-infested areas. Most losses are caused by overgrazing and drought.

The plant is most toxic before it matures, somewhat less as it dries. Antelopehorn milkweed retains enough toxicity to be dangerous in hay.

Although most animals die if they reach the convulsive stage of milkweed poisoning, some recover. Move them to shade, keep them quiet and give them plenty of food and water. No medicinal treatment is specified, but sedatives, laxatives and intravenous fluids may help.