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Herbs in the fight against internal parasites – myth or fact?

Herbs in the fight against internal parasites – myth or fact?
Photo: Archive

In the past summer's articles, I have covered internal parasites and your options for combating them as a supplement to the strategy you have developed with your veterinarian. This strategy involves testing manure samples for infectious eggs and larvae and administering specific deworming treatments. There are many suggestions for plants that can help horses combat internal parasites, and some of them likely have an effect. But what is myth, and what is fact? This article will give you an overview of the plants I have seen mentioned in this context, and which ones have scientific backing for their effectiveness in horses.

READ ALSO: Change pastures to reduce worm infection

About Martha Voss

Martha Voss is an equine agronomist and runs the independent consulting and course company NENUC, offering courses, consulting visits, and the development of educational games, among other services. Martha has more than 30 years of experience in teaching and research in horse management and proper nutrition.

As you likely know, it is biologically impossible to kill all parasites. Therefore, control strategies focus on inhibiting their growth to minimize harm to the horse:

  • Deworming treatments aim to kill as many parasites as possible.
  • Pasture rotation and hygiene reduce infection pressure in the field, as does co-grazing with other animal species.

Herbs offer several approaches depending on the plant, such as strengthening the horse's digestion and intestinal resistance or inhibiting the worms' development in the gastrointestinal tract. Therefore, it is a complex area, and it can be difficult to make definitive statements. However, I will take a chance and provide you with a list—both with good and bad news about the plants.

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Strengthening the horse's digestion and immune system

Most of the plants on this list work by improving the horse's digestion in one way or another. The plants listed below primarily work through their content of digestible fibers, but also through tannins and phenolic compounds that can affect worms, eggs, and larvae in various ways. Over the years, there has been global research on the effects of herbs on parasites in cattle and sheep, and studies on horses are beginning to emerge as well.

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Sainfoin (Onobrychis viciifolia)

Sainfoin is one of the species with the most documented anthelmintic (worm-inhibiting) effects, mainly due to its high polyphenol content. French studies show that it can inhibit egg hatching and larval migration of strongyles. However, another study also shows that sainfoin can reduce the effectiveness of deworming treatments, so if you feed your horse sainfoin, this should be included in your strategy when discussing treatment options.

Research on sainfoin is ongoing, and it is one of the plants that is most closely monitored concerning horses and worm control.

That said, sainfoin has a very positive effect on the horse's digestion, and in the long run, a healthier horse can better protect itself against internal parasites.

Chicory (Cichorium intybus)

Chicory has historically been used for various health benefits, including potential laxative and appetite-stimulating properties. It also contains inulin, which can promote healthy digestion and gut flora. There is limited research specifically addressing chicory as a treatment for internal parasites in horses. However, its digestive-enhancing properties can benefit overall gut health and, thus, the horse's resistance. A recent French study shows that horses grazing on pastures with chicory reduce egg shedding and inhibit larval development. Chicory may, therefore, be a promising strategy against small strongyles (Cyathostomes).

Echinacea (Echinacea spp.)

Echinacea, particularly Echinacea purpurea, is known for its immune-boosting properties. It is often used to strengthen the immune system, which can help protect against parasites indirectly.

While echinacea is well-known for its immune-stimulating effects, there is limited evidence of its direct effect on internal parasites in horses. Its use is often aimed at enhancing general health and the immune system, which can provide indirect benefits.

Inhibiting worm development

Many plants in traditional herbal medicine contain toxins that directly inhibit worms, their eggs, or larvae. Most of our knowledge of their effects comes from human herbal medicine, but there are also practical reports and some trials regarding their effects on horses. The list below is long but likely incomplete, and research on horses is limited. Therefore, take their effects with a grain of salt. Many of these plants naturally grow in horse pastures, and if they are effective, they offer an easy and inexpensive solution.

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Tansy (Tanacetum vulgare)

Tansy is known for its thujone content, which has antiparasitic properties but requires caution due to its potential toxicity.

Historically, tansy has been used against parasites, but modern scientific studies specifically on horses are lacking. Tansy, with its distinctive button-shaped yellow flowers, grows in many horse pastures, and there are reports that horses only eat it at certain times of the year. Whether this has any significance regarding worm control, I will leave open.

Wild Carrot (Daucus carota)

Wild carrot has traditionally been used against worms, but modern research is lacking.

It is part of traditional veterinary medicine, but scientific studies on horses are scarce.

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Mugwort (Artemisia vulgaris)

Mugwort contains artemisinin and other compounds with known antiparasitic properties that may be effective against internal parasites.

There is limited specific research on horses, but artemisinin is well-known in treating malaria in humans and has antiparasitic potential. Mugwort is also a common plant in horse pastures, and most horses eat it during certain periods. It could be an interesting herb to explore further if considering its use in horses.

Garlic (Allium sativum)

Garlic is popular as a natural dewormer, although evidence of its effectiveness against internal parasites in horses is limited. It is popular as a supplement for fly deterrence.

It is used as a supplement in small doses, but more research is needed. Some studies even advise caution with large amounts of garlic.

Thyme (Thymus vulgaris)

Thymol in thyme has antiseptic and anthelmintic properties, but there is limited documentation on horses. Many herbal feed mixes, therefore, include thyme.

The potential is there, but more research is needed.

Is biodiversity the way forward?

Based on the above list and the studies I have reviewed, it may make more sense to work on ensuring biodiversity in horse pastures and then observe what the horses choose to eat and when in the season (and the worms' lifecycle).

The problem with grazing is that horses also leave toxic plants and weeds standing, leading to unhealthy pastures from the horse owner's perspective. This is where co-grazing with sheep can offer the advantages and disadvantages, I mentioned in a previous article.

As noted, several of the plants mentioned here are added to feed mixes, which is one way to control intake by providing it in the feed trough. However, we do not always know enough to precisely distinguish between what is beneficial and what is harmful, as it often involves the interaction of multiple factors.

READ ALSO: Controlling horse parasites with ruminants 

Sources


Ankri S; Mirelman D. Antimicrobial properties of allicin from garlic. Microbes and Infection, 1999.

Burke JM, Wells A, Casey P, Kaplan RM. Herbal dewormer fails to control gastrointestinal parasite infection in goats. Veterinary Parasitology, 2009.

Hudson, J.B.: Applications of the Phytomedicine Echinacea purpurea (Purple Coneflower) in Infectious Diseases. J Biomed Biotechnol. 2012; 2012: 769896.

Laroche, N; Grimm, P; Julliand, S; Sorci G. Comparing the anthelminthic effect of different dehydrated sainfoin pellets in vitro. Proceeding at EWEN 2024, Oslo.

Liwang Cui, Xin-zhuan Su. Discovery, mechanisms of action, and combination therapy of artemisinin.

Expert Review of Anti-infective Therapy, Volume 7, 2009 – Issue 8.

Malsa, J. et al.: Effect of sainfoin (Onobrychis viciifolia) on cyathostomin egg excretion, larval development, larval community structure, and efficacy of ivermectin treatment in horses. Parasitology. 2022 Sep; 149(11): 1439–1449.

Malsa, J. et al.: Chicory (Cichorium intybus) reduces cyathostomin egg excretion and larval development in grazing horses. Int J Parasitol Drugs Drug Resist. 2024 Apr; 24: 100523.

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