Deworming Advice From Horsemen’s Laboratory

Horsemen’s Laboratory has received several requests for information about deworming and what schedule we recommend. We do not recommend any specific deworming schedule. However, we do recommend deworming according to fecal egg count (FEC) results.

The standard thought is to deworm according to egg shedding category:

  • Low shedders (0-200 eggs/gm) 1-2 times per year
  • Medium egg shedders (200-500eggs/gm) 3 times per year
  • High shedders (500-plus eggs/gm) 4 times per year

Horsemen’s Laboratory recommends having fecal egg counts done every three months. After receiving 3 or 4 fecal egg counts with results all below 200 eggs/gm, an owner may only want to check every 6 months, which is certainly reasonable.

Many owners whose horses test negative (no worm eggs found on counting chamber) ask if they should deworm their horses anyway and we recommend they should deworm at least once a year. Horsemen’s Laboratory feels the best time to deworm in these situations is in November or December in most parts of the United States. We generally recommend an Ivermectin Praziquantel combination, as this is a combination that is effective against a wide variety of worms that effect horses and whose eggs do not always show up when a fecal egg count is done. The two products found most commonly that contain this combination are Equimax and Zimecterin Gold.

Zimecterin Gold has been the focus of some Internet articles that suggest it may be responsible for causing some swelling and occasionally ulceration of the lips, tongue and gums of the horse when given. I have spoken to the Merial representative about Zimecterin Gold who said they have received reports of 1 in 20,000 doses possibly causing these problems, but have been unable to reproduce them so they cannot determine what the cause may be. I have also spoken to the United States Department of Food and Drug Administration, and they said they have also had the problem reported to them, but they did not offer any more information than that.

This is generally what we recommend should be done about deworming; however, if you have specific questions concerning your horses’ worm control program feel free to contact me directly. Horsemen’s Laboratory also offers very reasonably priced consulting services, for more information, please check out our website.






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