Horse Worming and How to Treat these Equine Parasites
Horse worming is a common concern for horse owners.
These equine parasites can cause various health problems for your horse, including weight loss, colic, and even death.
Fortunately, identifying and treating common horse worms can help keep your horse healthy and happy.
We tell you more about these internal equine parasites and how to more effectively manage them in your horse.
One of the first points to note is that all horses with access to grazing will have worms.
They are a normal part of life for horses, and for most mammals, including humans.
The solution is to keep them under control rather than trying to eradicate them completely.
**Please note, the following information is general in nature and does not constitute medical advice. Always consult your horse veterinarian for proper medical advice**
Equine Parasites – What Are They?
Equine parasites are organisms that feed off horses, causing harm to their health.
Horses can have both internal and external parasites. Internal parasites include parasitic worms that live inside your horse’s digestive tract.
External parasites include ticks, lice, and flies that live on the outside of the horse’s body.
We’re focussing on internal parasites in this post, more specifically common parasitic worms.
Horse Parasites – Common Horse Worms
The most common types of parasitic worms in horses are…
Roundworms (Nematodes)
Strongyles (large redworms)
Cyathostomes (small redworms)
Ascarids
Oxyuris (pinworms or threadworms)
Tapeworms
Bots
Health Issues Caused By Common Horse Worms
Each of these worms produces various symptoms, particularly in horses that have large worm burdens.
Some can be deadly if not treated.
Roundworms, for example, especially redworms, can cause diarrhoea, weight loss, and poor coat condition.
Large redworms are particularly dangerous in large numbers because they migrate into intestinal blood vessels where they can do a lot of damage.
Pinworms can cause extensive irritation around the anus, causing the horse to scratch and potentially injure itself whilst doing so.
Severe tapeworm infestations likewise can lead to colic and blocked intestines.
Historically, these worms have been underrated but modern research indicates they can in fact cause a lot of intestinal damage, resulting in the abovementioned conditions, both of which can kill the horse.
Bot larvae, the stage that infects horses, can cause irritation to the soft tissues in the mouth whilst the hatched larvae may ulcerate the stomach lining, causing colic and even blockages. The larvae can also tear skin which may then become infected.
Identifying Worm Burdens In Horses
Many horses don’t show too many signs of worms until they’ve caused extensive internal damage. However, it doesn’t mean they don’t have them.
Research tells us that sometimes the healthiest looking horse on the property can be the one with the heaviest worm burden! And that the wormiest looking horse has the lightest (which means their ‘wormy’ looking appearance has other causes, most likely nutrition-related)!
It’s also important to know that even on the same property, not all horses will have the same worm burdens.
Some horses seem to be more ‘immune’ to worms than other horses, something that can be picked up with a faecal egg count.
Generally speaking though, some of the common clues that your horse may have a larger than ideal worm burden include…
Weight loss
Poor coat condition
Lack of energy
Diarrhoea
Potbelly appearance
Difficulty swallowing
Colic
Horse Worming – How to Treat Worms
Roundworms are becoming resistant to many of the compounds used in horse wormers due largely to the traditional ‘worm every 6 weeks and use a different wormer each time’ approach.
Today, the recommended approach is far more tactical and multi-faceted!
We know for instance that not all horses need the same worming regime. Some only require seasonal worming; others require more frequent worming.
Strategic Horse Worming Management
Overall, it’s now acknowledged that treating horse worms successfully requires a multi-faceted approach that includes…
De-worming medications
Faecal egg counts
Pasture management
Good hygiene practices
Common Horse De-Worming Compounds
Common horse de-worming compounds (anthelmintics) include:
Benzimidazoles or BZ (e.g., Fenbendazole and Oxfendazole) is effective against strongyles, roundworms, pinworms, and some tapeworms.
Macrocyclic lactones (e.g., ivermectin, moxidectin) is effective against strongyles, roundworms, bots, lungworms, and some external parasites like mites and lice.
Pyrantel pamoate is effective against roundworms, pinworms, and some tapeworms.
Praziquantel is effective against tapeworms.
Combination products – Some de-wormers combine two or more active ingredients to target a broader range of parasites.
Most horse worming compounds treat adult stages of worms.
They are also metabolised quite quickly by the body so only effectively kill worms for the short period of time they’re active, which is usually around 24 to 48 hours.
As the adult worms are killed off, encysted worms and eggs hatch to replace them.
Therefore, when a horse is heavily infested with worms, new worms quickly replace the eliminated ones and the cycle continues.
Currently, only one compound (Moxidectin) is effective in single dose against these ongoing waves of hatching worms because it is metabolised much more slowly, so ‘hangs’ around in the horse’s system for longer.
The other effective method is the 5-day Fenbendazole treatment. Fenbendazole is metabolised rapidly but it’s also very safe and can therefore be administered for extended periods.
So…the first dose gets rid of adult worms and encysted ones hatch to replace them.
The second dose gets rid of the newly hatched worms, releasing yet more encysted ones.
And so on for 5 consecutive daily doses. At the end of 5 days, most of the encysted worms should have hatched, and been killed off.
Many owners then follow this up with one of the other wormers 10 – 14 days later.
Faecal Egg Counts
Regular faecal egg counts (FEA) can help identify horses that have high worm burdens and require worming, vs those that don’t.
However, FEAs only measure the number of strongyle and ascarid eggs in manure. They don’t measure bots, pinworms, tapeworm, or encysted Cyathostomes.
Good Pasture Management For Horse Worm Control
Proper pasture management is also crucial in preventing horse worm infestations.
Clean your horse’s paddock regularly, remove manure, and rotate grazing areas to prevent your horse from continuously eating larvae or eggs from worm-infested areas.
If you like top-dressing your paddocks with manure (and it does a brilliant job), it’s best to wait until heat generated as it decomposes has killed off the eggs.
Practice Good Hygiene around your Horses
In addition to horse worming and pasture management, practicing good hygiene can also help prevent horse worm infestations.
Regularly clean your horse’s stall and equipment, wash your hands before and after handling horses, and avoid overcrowded grazing environments. These can all help reduce internal parasite burdens in your horse.
FAQs About Horse Worming
How often should I de-worm my horse?
This depends on several factors, such as their age, living conditions, and travel history. Generally, current theory is that horses should be de-wormed strategically as required.
For some horses, that may mean seasonally.
For others, it may mean every 3 months or so with rotational wormers.
Consult your veterinarian to determine the best de-worming schedule for your horse.
Can I see worms in my horse’s manure?
It’s rare to see worms in your horse’s manure unless they’ve just been wormed. But you will very probably see some types of worms in your horse’s manure after de-worming so long as you’ve used the right wormers for the types of worms your horse has.
Other types of worms though are too small to be visible to the naked eye, so missing them in manure doesn’t mean your horse doesn’t have them.
Can horse worms infect humans?
No, horse worms cannot infect humans. However, some types of horses’ internal parasites can cause serious diseases in humans, such as liver damage and blindness, through accidental ingestion of infected eggs.
Key Takeaways About Horse Worming
Horse parasites, specifically worms, are a common problem in horses that, in heavy infestations, can cause serious health issues for horses.
Talk to your vet about the best de-worming schedule for your horse and practice good pasture management and hygiene to help reduce horse worm infestations.
