What Types of Worms Are There and What Problems Do They Cause?
In this article, we will talk about 4 types of worms that can cause issues in horses. While this is not a complete list of the worms and parasites that could affect the health of your horse these are some of the most common.
Small Redworms (Cyathostomes)
This worm lives in the horses' intestines. It is one of the most common parasites in horses. The eggs are embedded in the intestinal wall. The eggs tend to go dormant during the winter and hatch when it is spring resulting in a sudden and large amount of parasites flooding the horse's body. The sudden flood of parasites that consume the horse's nutrients can be deadly. The symptoms they can cause are:
- Weight loss
- Diarrhea
- Colic
Large Redworms (Strongyles)
The term 'large redworms' incorporates several different varieties of strongyles worms. They are considered some of the most dangerous worms to infect horses. The eggs of the worms are ingested and then they make their way to the horse's bloodstream. While in the blood vessel they tend to obstruct blood flow, which causes damage to the tissue that is supplied by the said blood vessel.
Symptoms of these worms include:
- Colic
- Rapid weight loss
- Diarrhea.
Bots (Gasterophilus)
Bots are the worm form of the bot fly. When the bot flies lay their eggs on the coats of the horse, the horse tends to ingest them when they lick themselves to groom. Once they make their way into your horse's mouth, the bots hatch and are able to migrate to the stomach.
Symptoms include:
- Inflammation in the mouth
- Inflammation in the throat
- Ulceration in the stomach
Roundworms (Ascarids)
Roundworms are particularly dangerous for horses with a weak immune system such as foals and elderly horses. The parasite is consumed through contaminated food (grass that has come in contact with the fecal matter of an infected horse). The parasite migrates from the intestine to either the lungs or the liver. These worms can cause severe damage to these organs before returning to the intestines to lay their eggs and start the cycle again.
How Often Should I Deworm My Horse?
How often you need to deworm your horse will depend on certain factors. A key factor is how many eggs your horse is excreting in their manure. For most horses, twice yearly, often done in the spring and fall, is recommended. If your horse is highly infected then the frequency of doses should increase. We recommend consulting your veterinarian about how often your horse needs to be dewormed based on a fecal exam.
Deworming for foals is often done every 2 months for the first year with your foal's health being monitored with the help of regular fecal exams.
What Medicine Should I Use to Deworm My Horse?
The type of medication used will depend on the results of your horse's fecal exam. Depending on the type of worms present different dewormers will work better than others. Some common medicines are ivermectin and moxidectin. For the types of deworming medication we offer, please see our Equine Vaccinations & Prevention page.
Methods to Avoid Parasites
Besides deworming and regular veterinary examinations including fecal exams, some strategies that can help control parasites in horses include:
- Keeping a new horse quarantined while they undergo a precautionary deworming and a subsequent fecal exam.
- Removing fecal matter from pasture regularly to reduce chances of reinfection.
- Rotating pastures to avoid contamination.
- Avoiding overcrowding pastures by limiting the number of horses on each pasture.
How Can I Tell if My Parasite Control Program is Working?
The best way to tell if you're controlling the parasite is to have your vet do tests such as fecal exams, to gauge the health of your horses.
Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.