Page 66 - The Mini Horse Magazine 2023 No 1

of the toxin. Because horses do not metabolize
the cyanide compound as efficiently as ruminant
Johnsongrass/ animals do, grazing healthy adult plants is
Sudan grass unlikely to harm them, but circumstances that

(Sorghum spp.) injure the plant—wilting, trampling, frost—
can chemically liberate the cyanide within the
leaves, rendering them dangerous to all species.
Cultivated hybrids of Sudan grass typically
contain less cyanide, if any. Both species can
INFORMATIVE coarse-stemmed grasses with broad, veined overfertilized. Cyanide concentration drops to
also accumulate toxic levels of nitrates if
ID: Both Johnsongrass and Sudan grass are
safe levels when the grasses are cured for hay,
leaves that can grow to six feet in height. Both
but nitrates, if present, do not.
produce large, multibranched seed heads.
The danger: The leaves and stems of
poisoning. The first indication is rapid breathing,
Johnsongrass and Sudan grass contain a Signs: Signs are consistent with cyanide
cyanide compound, which when metabolized which progresses to tremors, frequent urination
inhibits the body’s ability to absorb oxygen, in and defecation, gasping and convulsions.
effect suffocating the animal; young shoots of What to do: Supportive drug therapy can offset
johnsongrass contain the highest concentration the effects of less severe cyanide poisoning.

A 1,000-pound animal has to consume
significantly higher quantities of most toxins

than a smaller animal does to feel any effects.

or blue, wooly, purple, Lambert’s, two-grooved
milk vetch, white-point—grow in varied terrains
Locoweed throughout.

(Astragalus spp. The danger: All toxic species of locoweed
or Oxytropis spp.) contain swainsonine, an alkaloid that inhibits

the production of the enzyme necessary for
saccharaide metabolism, and the resulting sugar
buildup disrupts the function of brain cells.

Signs: Strange behavior is usually the first
Also known as: Crazy weed evidence noticed; horses may bob their heads,
ID: Leafy perennials with short stems and adopt exaggerated, high-stepping gaits or
compound leaves that grow in tuftlike forms stagger and fall.
from a single taproot. Some species may be What to do: There is no treatment for advanced
covered with silvery hairs. The flowers, often locoism, and its effects are irreversible. Horses
white or purple, are borne on leafless stalks.
with less severe poisoning may recover when
Range: Different species of locoweed—spotted access to the weed is removed.

66 | Miniature Horse Magazine • Issue 1/2023