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Got Worms? Treating Equine Parasites

Equine parasite control was revolutionized in 1960 when the first of benzimidazole (BZ) anthelmintics where introduced. During the 1960’s the rotation between drugs came into effect. Since then, equine parasites have continued to increase resistance to the drugs.

The optimal method for treating equine parasites is by treating the horse with the right drug and not over-treating the horse. The method of treating parasites based solely on the calendar and not in response to the medical needs of the horse is no longer recommended. Some horses are highly susceptible to worms and considered ‘heavy shedders’, while others may only need dewormed once or twice a year.

What to Consider When Removing Equine Parasites

  • Age of the horse
  • Time of year
  • Parasite species and level
  • Brand of dewormer used last
  • When the horse was last dewormed


To help aid in the resistance to the anthelmintics (dewormer) each horse should be tested with a fecal egg count (FEC). The McMaster method is the common way FECs are performed. This method has a minimum sensitivity of 25 EPG, which in other methods would have had a negative result.

Contact our clinic to set up a fecal egg count to ensure your horse has not become resistant to dewormers.

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  • Penny King, Oblong IL

    I can’t say enough about Dr. Stone & his staff. They go above & beyond & take the extra mile to take care of your horses needs. They really care about what your horse really needs.

    They have been up all night with emergency colic surgery with a positive outcome. They saved a foal that was born three weeks early. I can’t even begin to tell everything we have been thru together. But I can tell you one thing, they don’t come any better than Dr. Stone & his staff. They are like family to our horses & us.”