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Parasite control: A horse health essential

June 7, 2018

Could there be potential internal invaders lurking in your horse's pasture?

Internal parasites often thrive in grazing areas and can easily afflict your horses. Some of the most commonly found equine parasites are large and small strongyles, roundworms, tapeworms, pinworms and bots. They can have debilitating effects, including, but not limited to, weight loss, diarrhea, anemia, coughing and liver damage. But there is hope. By establishing a regular, targeted deworming schedule designed to significantly decrease the numbers of these harmful pests, you can help your horse — and potentially other horses on the property — achieve better health.

You may be wondering how you could possibly help other horses. Some horses have a higher immune status than others and may not be as susceptible to the harmful effects of parasites. These horses may be chronic shedders, meaning that while they might not exhibit clinical signs of parasitism, they could be carrying a lot of adult worms, which are producing eggs that are then inadvertently spread to the shedder’s pasture mates. You may need to deworm chronic shedders more often than others in an effort to keep everyone healthier.

An effective deworming program needs to take several factors into consideration, including:

  • Age: Foals and other young horses are more susceptible to certain types of parasites (large and small strongyles, roundworms, pinworms, tapeworms and potentially threadworms).

  • Location: Different kinds of parasites are more common in different areas or climates.

  • Season: Some parasites, like bot flies, are only active during specific times of the year.

  • Travel: Horses that travel to shows may be exposed to infected horses and parasites they might not otherwise be exposed to at home.

  • Pasture: Many horses grazing in a given area may increase parasite exposure. Other animals may also shed parasites that could infect your horse.

The importance of fecal egg counts

The best way to determine your horse’s specific deworming needs is to have your veterinarian perform a routine fecal examination, also known as a fecal egg count (FEC), during which the feces are inspected for the presence of worm eggs and the eggs are then counted. From there, you can work together to evaluate the numbers and types of parasites and decide on a course of action.                                                                               

If possible, I recommend having a second FEC performed 10 to 14 days after deworming. This is known as a “fecal egg count reduction test” and will tell you if deworming was effective. Resistance to commonly used dewormers is becoming more prevalent, so it’s important to make sure there are fewer eggs in your horse’s manure after deworming.

Management tips

You may also aid in keeping parasite numbers down with good management practices:

  • Clean pastures regularly: Remove and dispose of manure at least twice weekly.

  • Rotate pastures: Move horses between pastures to naturally break parasitic life cycles.

  • Use elevated feeders: Lift grain and hay off the ground, where parasites thrive.

Lastly, I should clarify that your horse will — unfortunately — never be 100 percent parasite-free. All horses will always carry some worms due to the cycle of pasture grazing and fecal contamination. However, with some precautionary steps and targeted treatment, you can help your horse build a better defense against these would-be internal invaders.


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