A horse on pasture grazing is most likely to harbor which type of worm?

• A. Strongyles
• B. Roundworms
• C. Tapeworms
• D. Pinworms

Answer: (A)

Pasture grazing exposes horses to infectious larvae living on grass and soil, so the parasites that most commonly infect grazing horses are those with larvae present in the environment. Strongyles are the most frequent intestinal parasites in horses, and the small strongyles in particular are highly prevalent on pasture. Their larvae are ingested with forage and can persist and re-infect as the horse continues to graze, making this exposure pathway especially important in pasture settings. In contrast, roundworms mainly affect young horses and are less tied to grazing adults, tapeworms depend on mites found on pasture as intermediate hosts but are not as consistently encountered as strongyles, and pinworms tend to cause perianal irritation with less direct association to grazing exposure. So the typical pasture-associated parasite is the strongyle.