Kentucky Horse Council
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Lexington, KY 40511
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5-Jun-09 8:00 PM  EST  

Strategic Deworming 

The following information was derived from webinar on Strategic Deworming as instructed by Dr. Heidi Brady, PHD, Dipl. ACAP with the Department of Animal and Food Sciences at Texas Tech University. 

Deworming your horse is an inexpensive and relatively easy way to help him stay healthy and perform at his maximum level. Horses that are infected with internal parasites or worms will be less efficient (in their absorption of nutrients from feed) and may struggle with performance (breeding, sport, growth, etc).

Symptoms of horses that are infected with parasites may include: weakness, anemia, poor appearance, rough hair coat, pot belly, cough, digestive disturbances, colic, death. It is important to note that some horses that appear perfectly healthy have high levels of parasite infection making it difficult to rely on the symptoms alone to determine infection. Thus it is important to have a parasite control plan for your horse(s).

The best way to determine the level and type of parasite infection in your horse is to take a fecal sample to your veterinarian and have a professional perform a fecal egg count. Some classes of parasites, however, cannot be found on a fecal egg count. You should work with your veterinarian to develop the best deworming protocol for your horse herd based on egg count, exposure to outside horses and other species, geographic location, pasture management, etc. 

Scientists are reporting an increase in resistance to dewormers in the United States and other countries. The highest incidence of resistance is reported with small strongyles which are typically treated with Fenbendazole. Resistance is tested by performing fecal egg count reduction tests which include taking a fecal egg count prior to administering dewormer and 14 days post administration. 

Resistance to dewormer is caused by a variety of factors including: continued use of one type or class of dewormer, high frequency of deworming, administering incorrect dosage of dewormer (usually because of underestimating the weight of the horse).

Good management practices also contribute significantly to the control of parasites. Exposure to parasites can be reduced by: cleaning stalls and pens regularly, composting manure before spreading, avoiding ground feeding, avoiding overcrowding, quarantine new animals and perform fecal egg counts and deworm prior to introducing to the herd, prevent under dosing by using livestock scales or more accurate weight measurements, species rotation on pastures, remove animals from pasture and plant a crop or annuals, harrow fields when horses are off grass.

There remains a need for further study to determine the best approach to deworming horses, however three approaches are generally used: scheduled (using a rotational approach), targeted (deworming only when needed), and daily. Texas Tech University studied scheduled deworming using a rotational approach on horses that displayed resistance to dewormer. They found that a rotational plan continued to control parasites despite past resistance. 

Remember to work with your veterinarian to determine the best approach to managing your herd health including strategic deworming practices.

To view the full Strategic Deworming Webinar visit

4 Way Rotation utilized with success and reduced fecal egg count at Texas Tech University

February – Moxidectin (Quest)

May – Pyrantel (Strongid)

August – Ivermectin & Praziquantel (Equimax, etc.)

November – Larvicidal Does Fenbendazole (Safeguard or Panacur)


6 Way Rotation utilized with success and reduced fecal egg count at Texas Tech University

February - Moxidectin (Quest)

April - Pyrantel Pamoate (Strongid)

June – Fenbendazole 2x (Safeguard or Panacur)

August - Moxidectin (Quest)

October - Ivermectin & Praziquantel (Equimax, etc.)

December – Fenbendazole Larvicidal (Panacur Powerpac®)

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For additional information on this Horse Management article, please contact:

Essie Rogers
(859) 367-0509

Source: Kentucky Horse Council

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