FAQ – Deworming

Please note that rotational (every 8 week) deworming is no longer recommended due to parasite resistance issues. Fecal egg counts and strategic deworming is what is currently recommended.

Here are some helpful links about deworming your horse:

• AAEP Deworming Recommendations: https://aaep.org/guidelines/parasite-control-guidelines
• Deworming videos by Dr Nielsen: https://www.facebook.com/pg/GluckEquineResearchCenter/videos/?ref=page_internal
• A summary of the deworming recommendations by Dr Nielsen: https://www.facebook.com/groups/277077519400687/permalink/868698733571893/

Info on timing of deworming and the “killing frost” myth:

The practice of deworming at or around the first frost is somewhat misconceived. Here are a few facts to hopefully straighten this out a bit:

– there is no such thing as a “killing frost” for external stages of parasites (eggs and larvae). In fact, they actually prefer freezing temperatures as they survive very well under these conditions.

– what actually kills these external parasite stages is warm (hot) and preferably moist weather.

– this is because the infective stages of strongyle and ascarid parasites do not eat. This means that they can only live off of energy stores in the forms of lipids and carbohydrates within their bodies. Once these stores are depleted, the parasites will die. And the warmer it is, the more they move around and the quicker they run out of energy. In constant cold weather, on the other hand, there is no movement going on and if well protected by fecal matter and a nice layer of snow, they can easily survive until the next spring.

– now, there is no parasite transmission going on, when it’s cold outside. When temperatures are below 6 C, parasite eggs will not hatch and there will be no development of larvae to reach the infective stages. Considering that it is a prime goal of parasite control to decrease parasite egg shedding to lower the infection pressure, it makes extremely little sense to deworm at the beginning of cold weather. A good dewormer may knock those egg counts down for about 4 weeks, but then they come back – I bet you it is still winter in Canada 4 weeks after the first frost. So a deworming at this time will really accomplish nothing.

Parasite control (for strongyles) is really only meaningful during the parasite transmission season. And that ended long before the first frost.

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