The environment of your horse is likely to transmit parasites that can, if not treated regularly, cause many diseases. To avoid a massive infestation in your horse it is therefore recommended to worm regularly.

What are the major internal parasites that my horse can catch?

Here is a list of the major internal parasites found in the horse and their consequences in cases of infestation.


1. Bots

Horses are infected by ingesting eggs present on the coat.

Consequences: salivation, gastritis, gastric ulcers or stomach cramps.

2. Ascaris

This is the largest parasite found in horses (15-40 cm long).

Consequences: digestive disorders, delayed growth, respiratory signs, cough.

3. Large strongyles

Horses become contaminated by ingesting larvae present on the pastures.

Consequences: parasitic aneurysm, internal bleeding, hepatitis, pancreatic cysts,

digestive disorders or colic.

4. Small strongyles, or cyathostomes

Horses become contaminated by ingesting larvae present on the pastures.

Consequences: the severe release of large numbers of larvae on the intestinal wall

can be fatal. Their regular output creates an inflammation which is responsible for

stomach cramps, diarrhea, fever, weight loss…adult parasites may be responsible for

digestive disorders during the grazing season.

5. Tapeworms

The larvae are hosted by prairie mites (Oribatida).

Consequences: enteritis, spasmodic colic, intestinal obstructions.

6. Strongyloides

Young foals become infested by ingestion of larvae from their mother (transmission

through milk) or a contaminated environment (damp litter).

Consequences: greenish diarrhea among foals aged from 2 weeks to 2 months or more, which can cause death.

7. Pinworms

Horses become infected by ingesting eggs present in the box but also the pasture.

Consequences: anal itching, depilation of the tail.

8. Habronemas

These roundworms migrate into the oesophagus and/ or stomach according to the species.

Consequences: rarely symptomatic, stomach pain.

9. Trichostrongles

Horses host it in their stomach after ingestion of larvae from pasture, especially when grazing with cattle.

Consequences: rarely symptomatic, possibility of stomach pain.

10. Ringworms

Very long and thin, these roundworms are also called ringworms. The adult parasites are located around the ligaments.

Consequences: rarely symptomatic, possibility of allergic contact dermatitis associated with the presence of microfilaria in the dermis.

11. Respiratory redworm

Horses become infested by ingestion of eggs or larvae on pasture. They infest especially donkeys and horses that are side by side.

Consequences: cough, difficulty breathing.

How can I fight these pests?

There are many molecules contained in wormers that are able to eliminate the parasites present in your horse. Each wormer therefore does not have the same sphere of action, in other words a particular wormer does not act on all types of parasite. That is why it is recommended to worm with different wormers throughout the year in order to eliminate as many as possible of the different parasites.

I need to worm my horse, but how many times per year?

In order to perform a correct worming programme it is advisable to worm between 2 and 4 times a year (for stabled horses), at regular intervals. To find out which wormer to use seek advice from your veterinarian.

Wormers are most widely available in the form of an oral paste, dispensed from anadjustable syringe depending on the weight of your horse.

Is there no risk of resistance to wormers?

Like irrational antibiotic use, repeated worming using the same wormer can lead to resistance. To avoid this, it is strongly recommended to perform a coproscopy

(research of eggs or larvae in the dung) to target which pests to deal with and thus to administer the best wormer accordingly.


In conclusion, talk with your vet to discover which worming programme is best for your horse!