Page 65 - The Mini Horse Magazine 2023 No 1

Hemlock Tansy
(Conium ragwort
maculatum) (Senecio spp.)

Also known as: poison hemlock, spotted Also known as: Tansy ragwort, groundsel
hemlock.
ID: A multistemmed weed with alternating
ID: A multistemmed perennial weed with leaves that produces clusters of small daisylike
toothed, fernlike leaves and clusters of small yellow flowers.
white flowers. The stems have purple spots, The danger: Levels of toxicity vary among
which are most evident near the base of the plant. different members of the species, but all are
The danger: Hemlock leaves, stems and thought to contain at least some concentration
seeds contain several potent neurotoxins that of pyrrolizidine alkaloids, which inhibit cell
affect both the central and peripheral nervous division, especially in the liver. Damage to the
systems. Four to five pounds is a lethal dose for liver is cumulative and irreversible, and most
a horse. Most animals will avoid the plant. horses succumb to chronic exposure over time,

Signs: Signs appear within an hour or two after consuming between 50 and 150 pounds,
of consumption, starting with nervousness, in total.
tremors and incoordination, progressing to Signs: Often, there is no evidence of
depression and diminished heart and respiratory consumption until signs of liver failure begin to
rates and possibly colic. Death results from appear: photosensitization, diminished appetite
respiratory failure. and weight loss, progressing to depression,
incoordination and jaundice.
What to do: There is no treatment, but if smaller
doses were consumed, animals may recover What to do: There is no treatment for advanced
with supportive care. stages of liver disease due to this toxin.

Text written & photographs provided by: Jarmila Podzemska
Yellow star flowers range from purple to white; Russian
thistle/Russian knapweed has no spines or prickles.
knapweed The danger: Both plants contain a toxic agent

(Centauria spp.) that has a neurological effect on the brain that
inhibits the nerves and control chewing. The
poisoning is chronic in nature; to receive a toxic
Also known as: dose, horses must consume 50 to 200 percent
Barnaby’s thistle of their body weight over 30 to 90 days.
ID: Yellow star thistle is an annual weed that Signs: Affected horses may appear to have
branches out from a single base stem to form tense or clenched facial muscles, and they are
a spherical plant up to three feet tall; its round unable to bite or chew their food effectively.
yellow flowers are surrounded by stiff spines Weight loss is also common.
1/2 to 3/4 of an inch long. Russian knapweed
spreads via a creeping root system; its erect, What to do: There is no treatment, and any
stiff stems grow two to three feet high and neural damage is permanent. Euthanasia is
are covered with gray hairs, and its thistlelike recommended if the horse is too debilitated to eat.

Miniature Horse Magazine • Issue 1/2023 | 65