Ivermectin for Horses - Dosage, Use and Side Effects

María Besteiros
By María Besteiros, Expert veterinary assistant and canine/feline hairdresser.. Updated: February 28, 2024
Ivermectin for Horses - Dosage, Use and Side Effects

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Ivermectin is a long-known antiparasitic used for various purposes in different species of animals such as dogs, cats and even humans. Ivermectin's ease of use, broad spectrum of activity and wide safety margin make it an ideal product for parasite control in horses.

The following AnimalWised article explains what ivermectin is used for in horses, how it works, and what contraindications there may be to its administration.

  1. What is ivermectin?
  2. What is ivermectin used for in horses?
  3. Ivermectin dosage in horses
  4. Contraindications and side effects of ivermectin for horses
  5. Symptoms of ivermectin overdose in horses

What is ivermectin?

Ivermectin is a very popular dewormer that has been used in horses since the 1980s. Ivermectin is commonly used to treat parasitic worms in the digestive tract of horses and other ruminants. These parasites often infest horses while grazing, migrate through the intestine, develop there, and then lay eggs that can escape through the animal's feces and infest fresh pasture.

The compounds of this class bind selectively and with high affinity to glutamate-gated chloride ion channels found in invertebrate nerve and muscle cells. This leads to an increase in the permeability of the cell membrane to chloride ions with hyperpolarization of the nerve or muscle cell, resulting in paralysis and death of the parasite.

As resistance to anthelmintics increases, ivermectin kills only a minority of these parasites. This resistance is due to the fact that the same anthelmintics have been used for the past 40 years.

If you want to know more about the different types of parasites that can affect horses, read this other article on horse parasites.

What is ivermectin used for in horses?

As mentioned earlier, ivermectin is an antiparasitic agent used to treat intestinal parasites. However, ivermectin is not effective on all parasites, so it is important to know which parasites it is effective on. Ivermectin, in particular, is capable of eliminating adult forms and some larval stages of several internal parasites that normally infest horses. Here are some of them:

  • Strongylus vulgaris: commonly known as the bloodworm, is a common parasite in horses from the phylum Nematoda. It looks like a long worm with a large, biting mouth.

  • Dictyocaulus arnfieldi: also known as bovine lungworm.

  • Parascaris equorum: is a species of ascarid, the equine roundworm. Among horse owners, the parasites are colloquially called "ascarids."

  • Trichostrongylus axei: a common parasite in ruminants, can infect horses, but the burden is usually low.

  • Strongyloides westeri: is an intestinal nematode that commonly affects young foals and is associated with small intestinal enteritis leading to diarrhea.

  • Onchocerca: is a genus of parasitic roundworms that infect humans and animals, especially cattle and horses.

  • Gasterophilus: commonly known as the fungus gnat, is a genus of parasitic flies that infest various animal species, especially horses, but cows, sheep, and goats can also be infested.

It is important to keep in mind that horses can also suffer from all types of external parasites, including ticks. Read on in this other article where we explain how to treat ticks in horses.

Ivermectin dosage in horses

The recommended dose of oral ivermectin for horses is 0.2 mg per kg, but as with any other drug, the veterinarian must determine the periodic deworming programs or specific treatments and the dosage and pattern of use.

Administering ivermectin in paste or gel form to the horse is usually easy, as it comes in a syringe with different divisions according to kg weight. So you only need to mark the division that corresponds to the weight of the horse to get the required dose.

It is administered by placing the tip of the syringe in the space between the teeth and premolars on the side of the mouth. The syringe is squeezed to hold the paste in the mouth, and the horse's head is raised slightly for a few seconds to facilitate swallowing. Before inserting the syringe, make sure the horse does not have any food in its mouth, as this may make it difficult to absorb the paste.

In addition to treating specific parasite problems, horses need to be dewormed several times a year from 6-8 weeks of age, especially foals and pregnant mares. The frequency of deworming depends on the characteristics of each animal and its living conditions and is determined by the veterinarian.

Ivermectin for Horses - Dosage, Use and Side Effects - Ivermectin dosage in horses

Contraindications and side effects of ivermectin for horses

Ivermectin should not be given to horses that have previously shown an allergic reaction to the product.

In some cases, adverse effects such as itching, inflammation or edema may occur in horses infested with large numbers of microfilariae. This is a reaction related to the death of the microfilariae and not directly to ivermectin. The clinical signs usually resolve spontaneously within a few days, although treatment is sometimes needed to relieve them. If these signs do not subside, you must consult a specialist. In any case, we must inform the veterinarian of any problem that the horse shows and that we think may be related to the use of ivermectin.

Ivermectin is considered safe for pregnant mares, but it is known to pass into the milk during lactation, and there is no information on the possible effects on the newborn foal. Therefore, the use of ivermectin is at the discretion of the veterinarian.

Ivermectin for horses should never be made available to other animals such as dogs and cats because if they swallow it, they could develop serious and even life-threatening adverse reactions due to the excessive concentration of the product.

Symptoms of ivermectin overdose in horses

Although ivermectin is considered safe for horses according to veterinary recommendations, a higher dose than the animal needs based on its weight may have adverse effects. Some of these are mild and temporary, meaning they subside quickly, but others become more serious and can even be life-threatening. Some of these include:

  • Pupil dilation
  • Lack of coordination
  • Lack of energy
  • Tremors
  • Coma
  • Death

If you suspect your horse may be poisoned, contact your veterinarian immediately. Tell him as much as you can about where, when and how the poisoning happened. Never try to treat your animal yourself. This could endanger your horse and possibly you.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Ivermectin for Horses - Dosage, Use and Side Effects, we recommend you visit our Medicine category.

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Ivermectin for Horses - Dosage, Use and Side Effects