I was speaking to a friend who runs a Livery yard, and we were discussing different worming products and the dangers of Horse Manure to dogs who have been treated with an Ivermectin based wormer.

Horses in the UK are generally wormed once or twice a year, and most owners will worm them just before the grass starts to grow in February/March.

Most horse wormers contain Ivermectin which can be fatal to our Collies and most dogs will be drawn to fresh horse manure, although ivermectin within the manure can remain active for some time.

Initial symptoms could be similar to those of a stroke with dilated pupils and an unsteady gait with possible seizures, difficulty breathing and eventually a coma. Ivermectin toxicity cannot be reversed, and if the drug has been digested within 4 – 6 hours, your vet may induce vomiting and/or give your dog activated charcoal to help minimize the amount of ivermectin that is absorbed.

Treatment will depend on the symptoms and may include giving your dog fluids directly into a vein and placing your dog on a ventilator, maintaining your dog’s body temperature, or administering medication to control seizures.

A breeder asked her vet when it was safe to exercise her Collies on land that had been used by horses, here is the reply from Norbrook who make Noromectin.

Levels of Ivermectin are strong in horse/sheep/cow poo for 3-4 days after dosing with Ivermectin wormers levels in voided poo break down rapidly in sunlight levels in fresh poo decrease to low by 14 days after dosing in horses and sheep, and 21 days in cattle

So - if you remove all livestock from the field, it will be safe for the dogs to play in after a 2-3 weeks if horses/sheep or a month if cattle ( to be safe )

Note - symptoms may not be apparent immediately, it depends on how fresh the manure is and how much your dog has eaten, it could take weeksto show any ill effects.



Meet Oliver Lotter! Oliver is being highlighted today to remind us all of an important concern regarding Ivermectin dewormer.

Oliver is an Australian Shepherd owned by Maria Lotter, a client of Bend Equine. Maria recently performed her routine Spring deworming to her horses with an Ivermectin product. The following day, Oliver began showing signs of neurologic disease (unable to rise, drooling, panting, urinary incontinence, blindness). Maria rushed him to the Animal Emergency Center in Bend where they diagnosed him with Ivermectin Toxicity. Oliver spent 7 days in the intensive care unit and is now recovering at home. He is still not back to his normal self and his veterinarian believes it could take another couple of weeks to return to normal.


1. Certain dog breeds have a gene mutation that causes them to be prone to Ivermectin Toxicity. These breeds include but are not limited to collies, Shetland sheepdogs, Australian shepherds, English shepherds, and Old English sheep dogs. A test is now available through Washington State University to determine if dogs have the gene that causes Ivermectin sensitivity.

2. Dogs can be exposed to Ivermectin after eating horse's manure that have been treated with Ivermectin. Horses pass the Ivermectin treated feces for 9 hours to 11 days after being treated.

3. Onset of clinical signs of toxicity in the dog occurs 4-12 hours after exposure. Signs include: depression, disorientation, vocalization, stupor, ataxia, tremors, vomiting, not eating, unable to rise, blindness, seizures, coma, and death.

It is very important that you keep dogs out of the area while horses are being dewormed with Ivermectin or moxidectin (Quest) to prevent accidental exposure of sensitive dogs to spilled product and, as shown above, exposure of dogs that eat horse manure even up to 11 days after deworming. Oliver was very lucky to have a diligent owner that noticed the toxicity quickly and to have had excellent care at the Animal Emergency Clinic in Bend.

We all wish him a speedy recovery!

Veterinary Centers of America
American College of Veterinary Surgeons
UC Davis
Washington State University
American College of Veterinary Surgeons
Dogs Naturally
Dr Conor Brady

This information is not meant to be a substitute for veterinary care. Always follow the advice provided by your veterinarian.