Equisetum arvense (field horsetail, common horsetail, bottle brush, Dutch rushes, paddock-pipes, pewterwort, shave brush), Equisetum palustre (marsh horsetail). A member of the plant family EQUISETACEAE. Perennial herbaceous plants, with short upright, green stems arising from creeping rhizomes. The fertile stems are usually irregularly branched; the sterile stems do not have branches but have a spore-bearing sword-like tip.

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Animals most affected
Cattle, (horses).

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Etiology
Ingestion, over a prolonged period of time, of fresh plant material (uncommon) or of contaminated hay or silage.

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Toxicity
Contains:

• A thiaminase with anti-vitamin B1 activity, responsible for weakness and falls in horses;


• Alkaloids: equisetine, heterosides, galuteoside;


• A high silica content.

The toxicity is not reduced or modified by drying. Ingestion of hay containing 5% horsetail for several days causes clinical signs.

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Clinical features
Generally present as a subacute or chronic poisoning.

In cattle

• Weakness, fall in milk production;
• Black diarrhoea
• Difficulty in walking and in getting up
• Haemoglobinuria (occasional)
• (excitation and blindness have been reported in a few cases)
• possibly death.

In horses

• Ataxia, mydriasis
• Hyperexcitability, progressive weakness, loss of weight.

Note: ingestion of a large amount of the plant material causes rapid onset of salivation, severe colic and excitation. Possibly death.

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Lesions
Hepatic and renal degeneration.

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Treatment
In cattle
No antidote. Symptomatic care only:

• Cardiorespiratory stimulants.
• Adsorbents, gastric demulcents

In horses

• Vitamin B1