• Horse and livestock manure can contain a chemical used in worming treatments called ivermectin
  • Small amounts pose a health threat to some breeds but most dogs will not be affected
  • Symptoms of ivermectin poisoning include dilated pupils, disorientation, lethargy and vomiting
  • Dogs showing any of these signs or known to be at risk should be seen by a vet immediately

Many dogs have a tendency to eat things they shouldn’t when out and about, including horse and livestock manure. Although it’s one of the least desirable habits among our four-legged friends, most breeds of dog that eat a small amount of manure will not become ill. But there is a risk of toxicity due to chemicals in worming medications which will be passed in the faeces, and for this reason dog owners – particularly those with certain ‘at risk’ breeds (see below) – should avoid letting their pets consume it.

A dog looks up at a pony
Some dogs are at a high risk of poisoning from horse manure.

Why can horse manure be dangerous to dogs?

Horse worming treatments often contain a chemical called ivermectin which is effective against many different parasites across a range of species. It is also used as a wormer in cattle and sheep. Outside of the UK, some worming medications for dogs include the chemical but in very low doses managed by a vet that cause no harm.

There is a far higher concentration of ivermectin in horse and livestock worming treatments and this can passed in manure for days after the animal has taken the medication. This can be toxic to dogs that eat it, but the risk depends on the breed of dog, when the animals were treated and the amount consumed.

What breeds are most at risk from ivermectin poisoning?

Any dog that consumes a large amount of horse poop containing the chemical could become very ill, but a percentage of dogs of certain breeds have a gene mutation which predisposes them to toxicity from ivermectin at low levels. These include collies, Shetland sheepdogs, Australian shepherds, Old English sheepdogs, long-haired whippets, merle Pomeranians and possibly other herding breeds as well as those with white feet. A test for the gene mutation which puts dogs at high risk can be done so you can check whether your pet is at risk. Toxicity in breeds that don’t have the genetic predisposition to being affected by ivermectin in low doses is very rare.

A dog walks along beside two horses

What are the symptoms of ivermectin toxicity?

Symptoms of ivermectin toxicity include dilated pupils, a lack of balance, disorientation, lethargy, vomiting, drooling and seizures.

What should I do if I suspect ivermectin poisoning in my dog?

If your dog has eaten horse manure and begins to show symptoms of ivermectin toxicity, they should be seen by a vet immediately. Without prompt veterinary attention, ivermectin poisoning can be fatal.

What treatment can be given for ivermectin poisoning?

There is no antidote to ivermectin toxicity, but with supportive veterinary care most dogs will have a good chance of recovery. This will, however, very much depend on the amount consumed and whether or not the dog is sensitive to ivermectin.

How do I stop my dog from eating horse poop?

Early training to teach your dog to ‘leave’ whilst out and about should enable you to stop them eating horse and other animal’s manure, but keep a watchful eye over them, particularly if the dog is from an at-risk breed. For dogs who are determined scavengers despite training, their owners can consider muzzle training. All dog owners should be extra vigilant around stable yards and farms, especially at times when horses and livestock are known to have been wormed.  

— Page last updated 15/01/2018