Is Horsetail Toxic to Dogs?

⚠️ Mildly ToxicSeverity: Moderate

✅ Cross-checked against veterinary poison-control guidance · Oct 2026 audit

⚠️ Educational info only. If your pet just chewed something and looks unwell, skip the reading and call your vet or Pet Poison Helpline (US): (855) 764-7661.

Horsetail is mildly to moderately toxic to dogs. One graze causes GI upset, and repeated eating causes vitamin B1 loss with weakness over time.

Also known as: Scouring Rush, Snake Grass, Field Horsetail, Equisetum arvense · Equisetum arvense

What makes it toxic

Thiaminase, which breaks down vitamin B1, combined with abrasive silica and mild gut irritants. Chronic intake is what produces real deficiency.

Warning signs to watch for

Vomiting and diarrhea acutely; with repeated grazing, weight loss, hind-limb weakness and incoordination from thiamine depletion.

What to do if your dog eats it

Keep the dog away after any meal of it and watch for GI signs. For dogs that have grazed it repeatedly, ask your vet about thiamine supplementation.

Common questions

Is dried horsetail in horse hay a danger to my dog?

Yes — drying does not destroy thiaminase, which is why it is a known horse problem. Keep dogs from raiding hay and feed storage too.

How much horsetail causes thiamine deficiency?

It takes repeated meals, not one incident. The pattern matters more than the single dose, which is why breaking the habit is the fix.

More plants checked for dogs

Pothos☠️ ToxicYes, pothos is toxic to dogs. Chewing any part of the vine releases calcium oxalate crystals tha Aloe Vera⚠️ Mildly ToxicAloe vera is mildly to moderately toxic to dogs. The skin and latex layer of the leaf contain co Spider Plant✅ Non-ToxicNo, spider plants are non-toxic to dogs. A dog that nibbles the arching leaves is not at risk of Easter Lily⚠️ Mildly ToxicEaster lilies are only mildly toxic to dogs — they usually cause stomach upset, not the fatal ki Sago Palm☠️ ToxicYes — sago palm is severely toxic to dogs, with a documented fatality rate around 50% when untre Boston Fern✅ Non-ToxicNo, Boston ferns are non-toxic to dogs. Chewing a frond will not poison your dog.

This page is general educational information, not a substitute for professional veterinary advice. Every pet is different — if your animal ate something concerning, contact your veterinarian or a pet poison hotline right away. Checking what your pet can eat? Visit our sister site SafeOrToxic.