Two-grooved milk-vetch
General poisoning notes:
Two-grooved milk-vetch (Astragalus bisulcatus) is a native plant found on rangelands in western Canada. This plant can accumulate quantities of selenium high enough to cause toxicity in cattle, horses, sheep, and swine. High quantities of selenium cause acute toxicity, with symptoms including staggering, diarrhea, prostration, and abdominal pain. Plants that contain a selenium content of less than 200 ppm cause chronic toxicity. James et al.(1983) used this plant (selenium content of 180 ppm) to conduct feeding experiments on sheep. They found that the symptoms and microscopic lesions of tissues collected from the sheep were similar to those caused by locoweed poisoning and not selenium poisoning. This finding suggests that other toxic compounds in addition to selenium may be present.
Swainsonine is also found in this plant, which may explain why, in experiments, sheep exhibited symptoms more appropriate to locoism than to selenium poisoning (Cheeke and Schull 1985).
Description
Astragalus bisulcatus is a herbaceous perennial with a thick woody root-stock, growing 30 to 100cms tall. It has numerous simple stems and long pinnate leaves. The flowers are produced in narrow elongated racemes. The flowers are a showy purple color and blooming occurs in late spring and early summer. The seed pods characteristically are two grooved on the upper surface. The fruits ripen and release their seeds in July and August. The seeds are dark brown or black, reniform in shape, 4 mm long and 2 mm wide.
Astragalus bisulcatus (Hook.) A. Gray
Nomenclature:
Scientific Name: Astragalus bisulcatus (Hook.) A. Gray
Vernacular name(s): two-grooved milk-vetch, silver-leafed milkvetch
Scientific family name: Leguminosae
Vernacular family name: pea
Geographic Information
Alberta, Manitoba, Saskatchewan.
Toxic parts:
Flowers, leaves, stems.
Notes on Toxic plant chemicals:
This plant is a recognized selenium accumulator. Selenium has been found to be toxic to sheep and cattle at levels of 4-5 mg/kg of dry matter. Two-grooved milk-vetch collected in Canada contained selenium at 43 mg/kg, well above the level required for toxicity (Davis 1986).
Toxic plant chemicals:
Selenium, swainsonine.
Swainsonine
Chemical diagram(s) are courtesy of Ruth McDiarmid, Biochemistry Technician, Kamloops Range Station, Agriculture and Agri-Food Canada, Kamploops, British Columbia, Canada.
Animals/Human Poisoning:
Note: When an animal is listed without additional information, the literature (as of 1993) contained no detailed explanation.
