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.
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.
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.
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