There are two common deworming strategies:

1. Strategic Deworming

Many of you are now familiar with the concept of strategic deworming that relies on fecal egg counts to identify which horses are high-shedders and are responsible for the majority of parasite transmission. The goal of this deworming strategy is not to completely eliminate all parasites from every horse, but to maintain the health of all horses and reduce environmental contamination of parasite eggs and larvae. The American Association of Equine Practitioners (AAEP) continues to recommend this approach for parasite control as it targets the horses that need deworming the most and helps to prevent further resistance to our current deworming medications. This is of concern as there does not appear to be any new classes of dewormers coming out for horses in the near future. Only 20% of horses within a herd are responsible for the majority of the parasite shedding. By targeting these horses, it can help reduce the number of deworming treatments required for the low-shedders of the herd, thereby reducing the exposure of the parasites to the deworming medications. The less the parasites are exposed to the dewormer, the less likely they are to develop resistance.

Fecal egg counts should be performed in the early spring (March to April) prior to peak parasite transmission season.  To be of the most benefit, every horse in the herd should be tested to identify them as low, moderate or high shedders so that they may receive the appropriate deworming treatment.  In general, all adult horses can benefit from two treatments per year. Low shedding horses may need no other additional deworming treatments. Moderate to high shedders will receive more treatments to reduce environmental contamination of parasite eggs and larvae.

2. Traditional Rotational Deworming

Traditional rotational deworming relies on using different deworming medications at regular intervals to control parasites. This strategy assumes that all horses carry a similar parasite burden and equally contribute to environmental contamination. It is convenient for many large barns and boarding facilities as it does not require fecal egg counts of every horse to identify high and low shedders. This approach is thought to contribute to parasite resistance of our current deworming medications. Contact your veterinarian to determine which parasite control program best fits your horse’s needs.