New Insights in Equine Parasite Control


Deworming horses according to their internal parasite load as well as instituting pasture and manure management practices are all integral to a good parasite program.

Controlling internal parasites is essential to keeping your horse healthy and performing at his best. High levels of parasitism may cause weight loss, a poor hair coat, and a depressed attitude. It may also cause more severe problems such as intermittent or persistent diarrhea, colic, and even death. Internal parasites are controlled by using anthelmintics (dewormers) and instituting management techniques to reduce the horse’s exposure.

Historically, deworming programs have centered on rotating types of anthelmintics and administering them every other month, year around. Unfortunately, this indiscriminant use of anthelmintics is causing increasing parasitic resistance to our current dewormers. With no new equine anthelmintics currently in production, horse owners face the threat that there will not be an effective dewormer in the future. This has led veterinarians to recommend deworming protocols based on each horse’s susceptibility to parasitic infection coupled with the known anthelmintic resistance found in the herd.

Every horse has some level of internal parasitism. By using fecal egg counts, efforts should be centered on identifying which horse is able, through his or her immune system, to clear most of the parasites and which horse struggles with the challenge. Each horse should be dewormed depending on his/her personal classification. In addition to this, identifying which dewormer is effective (or not) plays an important role in the deworming program. Ideally, initial fecal egg counts should be done in mid-summer to early autumn in Wisconsin when internal parasite eggs are most likely to be shed. The effectiveness of the  dewormer is determined by a second fecal egg count done 2 weeks after deworming the horse.

Strategic deworming alone will not diminish the advancement of parasite resistance. Horse owners must institute and abide by management practices that will limit their horse’s expose to internal parasites. Keep stalls, lots, and pastures clean of manure by picking them daily. Manure disposal can be challenging for many farms. Spread ONLY composted manure as the heat produced by composting destroys the parasite eggs and larvae. Isolate new horses from the herd until their parasite load is determined and they have been appropriately dewormed. Pasture horses of similar categories together. If possible, rotate pastures annually with other categories of horses or other species.

For more information, click here to view our deworming brochure or better yet, speak with one of our veterinarians during one of your horse’s visits.

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