The Dangers of Horse Manure for Dogs
Most horse manure is not poisonous to dogs, although eating it can cause digestive upset or expose a dog to parasites. A more serious risk may arise after a horse has been treated with certain wormers, particularly products containing ivermectin or moxidectin.
Why Some Dogs Are More Vulnerable
Some dogs carry a change in the ABCB1 gene, previously known as MDR1. This affects the way certain medicines are removed from the brain and can make an affected dog dangerously sensitive to some drugs, including high doses of ivermectin and moxidectin.
The gene variant is particularly associated with Collies and several related herding breeds. Dogs with one copy of the variant may also be sensitive, although reactions are generally more severe in dogs with two copies.
A DNA test is available. However, all dogs should be prevented from eating recently passed manure after horses or livestock have been wormed, regardless of breed or test result.
Signs of Ivermectin or Moxidectin Poisoning
Possible signs include:
- Unsteadiness, weakness or inability to stand
- Dilated pupils or apparent blindness
- Excessive drooling
- Vomiting
- Tremors or seizures
- Disorientation or unusual drowsiness
- Slow or difficult breathing
- Collapse, stupor or coma
Signs commonly develop within hours of significant exposure, but timing can vary. Do not wait for symptoms to appear before seeking advice.
What to Do
If your dog may have swallowed horse worming paste or eaten manure after a horse was recently treated with ivermectin or moxidectin, telephone your vet immediately.
Tell the vet the name of the wormer, when the horse was treated and approximately when the dog was exposed. Keep the packaging or take a photograph of its label if possible.
Do not attempt to make your dog vomit and do not give activated charcoal unless a veterinary professional specifically instructs you to do so. Vomiting can be dangerous once neurological signs have developed.
Veterinary Treatment
There is no specific antidote, but many dogs can recover with prompt and intensive supportive care.
Treatment depends on the exposure and symptoms and may include decontamination when it is safe, intravenous fluids, temperature control, breathing support, seizure control and careful nursing.
Recovery may take days or weeks in severely affected dogs. The outcome depends on the amount swallowed, the product involved, the dog’s ABCB1 status and how quickly treatment begins.
Preventing Exposure
- Keep dogs away while horses are being wormed.
- Clean up spilled paste immediately and dispose of used syringes safely.
- Do not allow dogs access to stables, yards or paddocks where recently treated animals have passed manure.
- Ask the horse owner which product was used and follow the manufacturer’s veterinary advice about exclusion.
- Use a lead or basket muzzle if your dog persistently eats manure.
There is no single waiting period that is correct for every worming product, animal or situation.
Avoid relying on a general rule such as two or three weeks. Check the precise product and obtain advice from the prescribing vet or manufacturer.