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Strategic Deworming: The Ins & Outs


This time of year there is much discussion about parasites and deworming. Frequent questions include: What product should be used? How often should my horse be dewormed? And why are fecal egg counts important? I hope the below summary can answer some of these questions for you and open your eyes to the modern deworming methods.

What are the goals of strategic deworming?

  • To control clinical parasitism and environmental contamination

  • To determine if parasites on the farm are resistant to any of the deworming products we plan to use

  • To prevent the development of parasite resistance to current deworming products

The goal of deworming is not to eradicate all parasites but to treat clinical problems related to parasites, control environmental contamination and treat each horse with a deworming protocol appropriate for them.

Why should we practice strategic deworming?

Each horse is an individual and they should be dewormed as such!

Historical theories on deworming were that more is better, but this in fact, is not the case! We have learned that deworming every 8 weeks is far more frequent than is necessary to control an individual horse’s parasite burden. Frequent deworming such as this has led to drug resistant parasites in many regions of the country, limiting our arsenal of effective dewormers.

How do we practice strategic deworming?

To determine how often your horse needs to be dewormed, and which deworming products should be used, we recommend performing fecal egg counts. A fecal egg count involves a microscopic examination of your horse’s manure, to look for and quantify the number of parasite eggs your horse is shedding. Horses can develop a level of natural immunity to parasites throughout their life via exposure however, this level of immunity can be affected by many things including stress, pregnancy, performance levels, aging, illness and PPID (‘Equine Cushing’s’). As this level of immunity can change, we recommend performing fecal egg counts annually or when there are changes in their environment or health status.

Horses that are high shedders should be dewormed most frequently and low shedders less frequently. Within any given population, 20% of the horses are shedding 80% of the parasites eggs into the environment, so only a small population of horses need be dewormed quarterly.

Environmental control is also highly important and this includes:

  • Routinely remove manure from pastures, paddocks and stalls every 1-3 days.

  • If ambient temperatures are <50 F consistently, can decrease to every 7-10 days

  • Do not spread manure on pasture unless properly composted

  • Avoid over-stocking and over-grazing of pastures

  • When possible, rotate pastures with other livestock (e.g. sheep, goats, etc) to break up the life-cycle of the parasites

The theory of this protocol is to deworm the horses that are high shedders more frequently to decrease pasture contamination.

What products should we use?

The product to be used will vary based upon the time of year, age of the horse, and shedding status (determined by the fecal egg count).

Regardless of the above information, it is important that every horse be dewormed at least once yearly with the following:

  • A larvicidal product (e.g. Quest, Quest Plus or a Panacur PowerPac)

  • To ensure efficacy against encysted small strongyles

  • Specific product recommendation will vary based upon age, sized and condition

  • A product containing praziquantel (e.g. Quest Plus, Zimecterin Gold, or Equimax)

  • To ensure efficacy against tapeworms

  • Specific product recommended will vary based upon age, sized and condition

For further details please see the strategic deworming schedules we have on our website or contact your veterinarian.

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