Janneke van der Wal founded Worm & Co in 2016. "I noticed that many horse owners were still choosing to deworm their horses routinely. This was often not out of ignorance, but due to a lack of information."

Why fecal testing?

"Until 13 years ago, you could simply get a dewormer for your horse anywhere. The legislation changed because research showed that gastrointestinal worms were starting to become resistant to the existing active ingredients in those dewormers. Since no new active ingredients are coming to the market, the only option left was to deworm based on fecal testing. Fecal testing involves counting the worm eggs in a stool sample. This way, you can determine if and which worms are living in the horse's intestines, whether there are too many, and if treatment is necessary. This approach is actually very logical. Just like you wouldn't take medication if you don't need it, so why should your horse? In the past, we didn't know better, but now we do. That's why I would advise everyone to make the switch if they are not already doing fecal testing."

Avoid deworming unnecessarily

"We work with veterinarians, as well as many stables such as Anky van Grunsven, Stoeterij Sterrehof, and Stal van Silfhout. Sadly, many stables still routinely deworm without fecal testing, often due to costs but sometimes for convenience. But routine deworming is truly unnecessary, and studies show that around 74% of horses in the Netherlands are dewormed unnecessarily. They receive medication they don't actually need! Every unnecessary deworming treatment contributes to worm resistance. We want to ensure that horses with actual worm infections can still be treated in the future. This won't be possible if all worms become resistant. By consistently doing fecal testing, preferably four times a year, you can track the cycle effectively and have optimal worm management. Fecal testing allows you to deworm specifically and only treat the horses that actually need it. If done correctly, maybe only 7% of the horses in a stable require treatment. Especially for the horse's health, it's better not to deworm unnecessarily. It's still medication, which can disrupt the body's balance and weaken the immune system. Especially the broad-spectrum treatment with the active ingredient moxidectin," explains Janneke.

What is worm resistance?

"Worm resistance refers to worms becoming insensitive to certain active ingredients in dewormers. Resistance is considered to occur when a dewormer, at the correct dosage, kills less than 95% of a worm species. For example, with redworms, we see that after administering a dewormer with ivermectin, worm eggs can sometimes be found again after just two weeks. A few years ago, this period was six weeks. With moxidectin, we sometimes see eggs again in the manure after eight weeks, while a few years ago it was three months. This clearly shows the existence of worm resistance. As horse owners, we can no longer ignore this issue. It's essential to use worming products that still work effectively," Janneke explains.

The best deworming strategy

Janneke: "The basic advice for every horse is to conduct fecal testing at least three to four times a year. Whether a horse needs treatment or the end-of-year dewormer depends entirely on the horse and the location where it is kept. For larger stables, we usually recommend a preventive deworming once a year, at the beginning of winter. However, this decision also depends on the overall health and age of the individual animal. If there are frequent changes in horses at a stable, the situation is different compared to when only two or three horses are kept at home, and manure is removed from the paddock or field. It's best to assess each horse individually to determine if deworming is truly necessary. Tailored advice is crucial because we need to move away from routine deworming."

Never completely free of worms

Janneke explains that having a worm-free horse is not the goal. "Every horse carries worms inside them, which is actually beneficial for the balance in the gastrointestinal tract. Different parasites in a horse's body help the horse develop immunity. If they aren't exposed to worms, they won't be able to build resistance. That's why foals are so vulnerable," says Janneke. "By monitoring horses through fecal testing, you'll see that from around 5 or 6 years old, they have fewer eggs in their manure. Eventually, they will only have negative results in their fecal tests because the horse has successfully built up immunity. Until then, fluctuations in the level of infection are common."

Worm cycle

Janneke: "The cycle of the redworm (the most common gastrointestinal worm) is six to eight weeks, but not all worms lay eggs. There are times when you won't see any eggs in the manure, even though there are redworms present. Due to this cycle, it's optimal to conduct fecal testing four times a year. This way, you'll always have a good sampling point and can address any infections promptly. When starting fecal testing, we recommend sending in stool samples twice within four weeks. If the results are negative both times, you can be certain that the horse isn't carrying too many eggs at that moment. If the first test is positive, you administer a treatment and use the second test as a follow-up. If the first test is negative and the second test is positive, it means the first test didn't align with the worm cycle."

What to do if worms are found in the manure?

Sometimes you may see worms in a horse's manure. Janneke explains, "This isn't necessarily a cause for panic. But if the manure is full of worms, there's a high chance of infection, and treatment is necessary. If you occasionally see a few worms, it's actually a good sign. The horse has expelled the worms itself, showing effective immunity. We tend to intervene quickly when we see worms. However, if the horse is otherwise healthy and fit, you can observe and let the horse resolve it on its own. If a horse isn't healthy, or if it shows symptoms despite a negative fecal test result, then you should seek veterinary advice. In such cases, there may have been a cycle where eggs weren't present during sampling. This is rarely seen in horse owners who conduct frequent fecal testing."

Not deworming at all?

Janneke: "The final fecal test of the year is usually between mid-October and mid-November. At the end of the year, you administer the end-of-year dewormer if necessary. Based on the results, the health, age, and a detailed questionnaire for the horse, our clients receive tailored advice. Not every horse requires or benefits from a heavy deworming treatment. If you prefer not to deworm preventively and your horse tests negative throughout the year, there's an alternative. The end-of-year dewormer with pramox is recommended because we can't effectively detect tapeworms through fecal testing. In recent years, the EquiSal saliva test has been developed. This test measures the amount of specific antibodies against tapeworms. It's a user-friendly test that can be self-administered using a special swab and sent to the laboratory. If the antibody levels are above a certain threshold, there may be a tapeworm infection requiring treatment. If not, treatment isn't necessary. If the EquiSal result is negative, but your horse tested positive 1 or 2 times in that year, it's important to assess the need for preventive treatment against encysted larvae on a case-by-case basis."

How does Worm&Co operate?

Throughout the years, Janneke and her team have gained extensive experience. "We focus on the needs of horse owners. We aim to simplify fecal testing, relieve our customers, and provide them with results and advice at any time. We believe it's crucial for owners to receive prompt test results. That's why we work with specialists at parasitological laboratories for the testing. We provide an online dossier for our clients where they can access their results and recommendations at any time. They can also share these with their own veterinarians or boarding clients, ensuring everyone is informed of the test results."

You can find Janneke and her team at: www.wormenco.nl