Common Name
Spotted or blue locoweed
Botanic Name
Astragalus lentiginosus
Plant Family
Dry, sandy soils of dunes and plains at lower elevations.
Animals Affected
Cattle, sheep, horses
Toxic Principle
Locoweed is poisonous at all times, even when dried. Swainsonine an indolizidine alkaloid found in all parts of the plant, inhibits the enzyme alpha-mannosidase which is essential for normal complex sugar metabolism in cells. these sugars accumulate in the cells of the brain and most other organs impairing normal cell function. Depending on the duration of locoweed consumption the affected cells can be permanently damaged. Swainsonine is secreted in the milk of lactating animals and will therefore affect the young animal suckling its mother.
Leafy-stemmed perennials with pinnately compound leaves. Leaflets number from 13-21 in a compound leaf. The blue-purple flowers are produced as racemes on stalks that are leafless. Pods are 2-celled with red-brown spots. Pods become papery when dry.
Weight loss, poor growth rates possibly due to poor absorbtion of nutrients from the intestinal tract.
Congenital Defects
Calves, lambs, and foals may be born with deformed crooked legs. Abortions and fetal death are common. Hydrops may develop in cows consuming locoweed. Some calves may be born weak and die shortly after birth. Decreased herd fertility is is a hall-mark feature of locoweed poisoning in cattle.
There is no effective treatment for locoweed poisoning. Animals should be moved from locoweed pastures. Recovery depends on the severity of lesions. Locoed horses should be considered permanently affected.
Nervous System
depression, incoordination, staggering gait, and unpredictable behavior especially if the animal is stressed or excited. Some horses become totally unpredictable in their response to handling and may fall down when being haltered or ridden. Poor vision, incoordination, sudden changes in behavior such as rearing and falling over backwards, often make horses dangerous and unsafe to ride. Cattle may become quite aggressive, and are difficult to work, especially through a chute.
Reproductive System
Abortions, hydrops, decreased conception rates. Decreased spermatogenisis.
Hepatic System
Weight loss and poor growth result from generalized vacuolated hepatitis causing decreased function. Liver enzymes are frequently elevated.
Serum can be submitted for the detection of swainsonine. The serum half-life of swainsonine is less than 24 hours. A serum profile of detectable levels of swainsonine, decreased alpha-mannosidase activity, and an increased aspartate aminotransferase is strongly suggestive of locoism. Detection of vacuoles in the cytoplasm of lymphoytes is suggestive of locoweed poisoning. Vacuoles in the cells of the brain, liver, lymph nodes, thymus, and uterus at post mortem examination is characteristic of locoweed poisoning.
Blue locoweed (Astragalus lentiginosus)sp