If you breed horses, or have a youngster then do you know your Strongyloides from your strongyles? Your ascarid from your pinworm and how to target each?
Parasites, particularly in young horses, pose a serious threat to health and development. Resistance only complicates matters: which chemical is effective against which worm, or whether a treatment is needed at all. That’s where worm egg counts, the cornerstone of good parasite control, come in.
Test First
Testing first helps determine the best course of action and whether there may already be resistance on your land to a given wormer. Generally speaking, fenbendazole and pyrantel are most effective against ascarids and pinworm; ivermectin and moxidectin for redworm (strongyles).
However, it’s not quite as simple as that; moxidectin should never be used on foals under four months old (six months if using a combination product with praziquantel) and is best reserved for winter doses targeting encysted small redworm. There’s now also concern over the efficacy of praziquantel and pyrantel (at double dose) for treating tapeworm.
The prevalence of ascarids in youngsters is one of the reasons we often lean toward older-style chemicals for them. But there’s always a time when we come up against anomalies - only testing can tell you what’s really going on inside your horses and on your land. It’s impossible to tell by eye whether a horse has worms, which type, or whether they’re resistant, so testing is essential.
That’s especially true in youngstock, who are more susceptible to worm burdens because their immune systems are still developing. While foals are especially vulnerable, all horses under five are classed as high risk under the CANTER parasite risk assessment. Without management, parasites like redworm, ascarids and tapeworm can cause stunted growth, colics, digestive upset, respiratory damage and even death.
Testing Programme
We recommend starting worm egg counts from 4 - 6 weeks of age, alongside a proactive worming programme until the foal reaches six months old. After that, we can safely transition to a targeted testing-based approach. Worm egg counts are advised every eight weeks until the transition to adulthood, to catch any rise in burden before it causes disease.
Monitoring this closely not only supports each foal’s healthy development but helps preserve chemical efficacy by reducing unnecessary treatments. Resistance is a growing threat, but with strategic testing, we can take control.
We’re encouraging breeders to put testing at the heart of good management because every horse deserves the best start. With Westgate’s easy-to-use postal kits, professional in-house lab and tailored support, we help take the guesswork out of parasite control.
As breeding season is in full swing, it’s one less variable to worry about. Healthy guts build healthy horses and that starts with informed parasite control from day one and we're here to help every step of the way.