Pinworms In Horses

Pinworms In Horses: What You Need To Know

Pinworms can be an annoyance to horses, but fortunately, that is the worst of it, as these intestinal parasites are relatively harmless. If you do suspect your horse is suffering from an infection, it is best to reach out to your vet for a diagnosis and treatment plan.

But, before we get ahead of ourselves, we will discuss the causes, symptoms, treatment and prevention of pinworms in horses. This treatable infection doesn’t pose a major threat to your horse, and is more just a bit of a pain in the bum!

What Are Pinworms?

Equine pinworms are formally known as Oxyurus equi. These parasites live in the colon of your horse – and they are actually fairly common. Infection with pinworms is also called oxyuriasis or enterobiasis.

Adult worms live in the large intestine of your horse, where they latch onto the intestinal walls.

Female worms lay eggs around the anus of the horse, which causes irritation, but this is also how these worms spread to other horses (more on that below).

Pinworms are found in many locales across the world, but they are more likely to crop up where several horse herds are kept in close proximity, with poor hygiene practices.

The life cycle of equine pinworms

The life cycle of pinworms is slightly different to many other worms found in a horse’s digestive system. In order to successfully treat these pesky parasites, you first need to understand how they reproduce and spread:

  1. Horses ingest the pinworm eggs. These eggs are usually present on contaminated surfaces where an infected horse rubbed its backside to get rid of the itch.
  2. The eggs hatch and live in the horse’s intestine. When there, the worms are actually mostly harmless.
  3. The female pinworms wiggle over to the horse’s anus where they deposit their eggs (and die in the process). The eggs are housed in a yellow, sticky substance – vets suspect it is this substance that causes itching.
  4. The eggs then either drop off or are rubbed onto surfaces, causing the worms to potentially spread to other horses.

These parasites have quite a long life cycle. From egg to adult can take up to five months! The immature adults have a resistance to dewormers, which can delay treatment to get rid of the parasite.

This video from Virbac Australia gives a very clear overview of the pinworm

Causes Of Pinworms In Horses

Any horse can be infected, but younger horses are typically more prone to infections. This is probably because they are still exploring their world, and end up putting their mouths all over different surfaces.

As mentioned, horses ingest the eggs that have been shed by infected horses. Once female pinworms lay eggs on the anus and it gets rubbed off, the eggs can linger on stall doors, fence posts and forage. A naive horse will eventually come into contact with them.

Symptoms Of Pinworms In Horses

Apart from a rather frustrating itch, pinworms really don’t have any severe symptoms. But, there are some ways to spot an infection, so keep an eye out for the following:

  • Horse rubbing its rump on trees, fence posts or stall doors
  • Restlessness
  • Inflamed, irritated skin around the tail
  • Patches without hair on the rump (due to rubbing)
  • Sores on the anus skin
  • Visible, yellow substance around the anus
  • Some eggs or adult pinworms could be visible in horse dung
  • In rare cases, young foals can suffer loss of body condition

This may seem like a bit of an odd request from me, but if you do notice a yellow, jelly-like substance under the tail, use some sticky tape to remove it. Yes, it is a bit gross, but it will help the vet diagnose the problem.

Diagnosing Pinworm Infections

Sometimes you may not even notice your horse has an infection until you take it for a routine physical at the vet. Other times you may notice adult worms and eggs in the faeces or sticking out around the anus, but that is relatively uncommon.

Most other worms are usually identified when spotted in dung, but pinworms very rarely make an appearance in your horse’s droppings. For that reason, a vet can’t do a faecal worm egg count to diagnose your horse.

The most common way to diagnose pinworm infections is to use a blunt scraper and scrape the area around the anus. Or, as mentioned above, sticky tape can be used on the anus skin to collect any eggs.

A vet will then look at the retrieved samples under a microscope. Luckily it is incredibly easy to identify pinworm eggs as they look different to many other parasites.


How To Treat Pinworms In Horses

Once your vet has confirmed that your horse has an infection, it’s time to start the treatment. There are two ways to treat pinworm infections – often used simultaneously. The first is using dewormers (also called “wormers”), and the second is maintaining a clean environment.

Here is exactly how to get rid of pinworms in horses:

1. Dewormers

Dewormers help to get rid of adult pinworms in the intestines.

Benzimidazoles have proven to be very effective against pinworms. Ivermectin and moxidectin are also reported to help get rid of the parasites, however, I have noticed them to be less effective.

Wormer kills pinworms in the large intestine, which is why it needs to be given orally.

Don’t apply wormers to the anus – it is very ineffective and will also cause environmental contamination if the horse defecates. Female worms die when they lay their eggs, so applying wormer to the anus will be pointless, anyway.

Horse wormer

2. Hygiene

Pinworm infections can be treated with good hygiene (along with the wormers mentioned above).

You need to first disinfect any areas your horse has come into contact with – stall surfaces, fences, trees, food bins. First, wash the areas with an eco-friendly soapy solution, then use a strong disinfectant. Do this every couple of days until you know your horse is in the clear.

Next, it is time to muck up – clean out any manure twice a day if your horse is in a stall, and try to remove manure from the pastures as well.

If your horse is rugged, make sure to wash all the rugs it came into contact with.

You should also gently wash the base of the tail and under the tail twice a day. Female pinworms move around at night, so an early morning clean is the best treatment. Once washed, apply petroleum jelly or coconut oil to the area. It will soothe the itch and prevent eggs from attaching.

Although pinworms spread, it is unlikely that the whole herd will be infected. You don’t have to treat all the horses, but do keep an eye on the other equines, especially the younger and older ones.

After two weeks of treatment and good hygiene (a practice I recommend you continue), use sticky tape to see if there are any eggs still present. If there are, it is time to call the vet again.

Preventing Pinworm Infections In Horses

The easiest way to keep pinworms at bay is to practice good hygiene at the stables or paddocks. Coupled with a consistent deworming schedule, you are unlikely to get any infections.

Here’s how to prevent pinworms in horses:

  • Don’t overcrowd the barn or pasture – it reduces the risk of parasite spread.
  • Regularly clean the horse’s environment. Scrub water troughs, feed bins, stalls and fences.
  • Don’t share grooming equipment between horses.
  • Wash your hands after handling your horse.
  • Keep infected horses away from the herd.
  • Any new horses should be quarantined until getting the all-clear from a vet.
  • Keep horses away from infected areas, including faeces in the field or an infected horse’s stable.
  • Regularly remove manure from the pastures.
  • Enforce rotational grazing.
  • Monitor your horses for any restlessness or rump-rubbing.
  • Ensure your horses have a well-balanced diet – this will improve their immune system.


What increases the chances of a horse developing a pinworm infection?

Pinworms are found across the world where there are horses. Young horses are more prone to getting an infection. This is because foals and yearlings use their mouths to discover their environment, causing them to come into contact with pinworm eggs.

Can older horses get pinworms?

Although more common in young horses, recently there has been a trend in adult and senior horses becoming infected. This is possibly due to an adaptation in adult pinworms, causing them to avoid detection by your horse’s immune system.

Can humans get pinworms from horses?

No, people can’t become infected with pinworms from horses. Although people can get pinworms, they only do so when in contact with an infected person. Humans can’t get pinworm infections from any animal species.

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