A lot of the propaganda floating around about natural dewormers sounds pretty convincing, especially when it’s presented with cautions about how harmful the chemicals in conventional paste dewormers can be.
However, the fact of the matter is there are no studies that proved to us the commonly recommended natural dewormers effectively eliminate intestinal parasites. As for how harmful a drug dewormer could be, well, any drug, herb, or even mineral for that matter, is potentially harmful and has its own safety profile and risk-versus-benefit ratio. Frankly, modern paste dewormers have a more favorable safety profile than common widely used drugs like penicillin or phenylbutazone.
Many herbals, as well as a variety of toxic metals (mercury, arsenic), have been used as dewormers both in humans and animals. However, most have the potential to be toxic as well, often with a narrow margin of safety or even a direct contraindication in horses. For example, black walnut is a common recommended natural dewormer for people, but it will cause severe laminitis in a horse.
Popular Natural Ingredients
Diatomaceous earth: The most popular ingredient in natural dewormers being marketed for horses is DE, or diatomaceous earth. DE is mined from ocean or lake beds and is rich in the skeletal remains of small organisms called diatoms. It is composed of over 80% silicon dioxide and another 8% or so of aluminum oxide and iron oxide. The remainder is a mixture of calcium, magnesium and other mineral oxides.
Finely pulverized DE powder is effective topically against ectoparasites (e.g. lice, ticks). It also works well in the environment to control a variety of insects. Microscopically, the powders have an irregular, sharp, spiny surface that damages the cuticules of insects, causing them to dehydrate rapidly and die.
DE is effective against all life stages of insects. The easiest to target are ground crawlers/larval stages, but it can also be mixed with attractants to lure in flying insects. However, once DE is wet, whether from water, saliva or stomach fluids, it loses its microscopic “cutting” edges and is no longer effective against insects. It’s also not a risk to the horse’s intestinal tract, even for horses with ulcers.
DE is approved by the FDA/USDA as an additive to grains in storage facilities and as an aid in preventing insect infestations. It can be added at a rate of up to 2% in grains intended for feed (40 pounds/ton = 0.32 oz/lb).
We’re betting your interest is piqued. Ours was, too. But using DE as a topical insecticide is a big leap from using DE to kill parasitic worms inside the horse’s digestive tract. In fact, we found no solid evidence to prove that feeding DE will kill parasites in a horse’s digestive tract.
Actually, when you think of it, why isn’t there any substantial evidence available' A manufacturer should be able to confirm antiparasite action simply by taking two groups of horses with similar parasite burdens, feeding DE to one group and no treatment to the other, while all other management conditions remain the same. But no such studies exist to our knowledge. In addition, wetting DE destroys its ability to kill insects by contact, and your horse’s intestines contain many gallons of fluid.
About the only way we think DE could help control intestinal parasites is if it has a feed-through effect. If manure containing parasite eggs is spread sufficiently thin to allow it to dry, the dried DE powder would again be active against any hatched larval forms. However, the powder has to be dry to work and that level of drying is itself lethal to parasite larvae.
If you want to try DE as part of a comprehensive parasite-control program, apply it liberally to the ground under and for a few inches around, those areas where accumulated manure has been removed.
Garlic: Although garlic is a favorite natural dewormer ingredient, we could find no justification for its inclusion. Concentrated garlic liquids are sometimes used by gardeners to discourage vegetable worms from attacking root and bulb crops. But it doesn’t kill them; it helps repel. And some vegetable worms actually attack garlic bulbs.
The repelling effect also requires strong garlic solutions, far greater concentrations than would ever be achieved in your horse’s intestine by feeding small amounts. Feeding large amounts, or concentrated garlic liquids, isn’t a good idea either because of the potential to cause Heinz body anemia in your horse.
Wormwood (Artemisia): Chemicals derived from sweet wormwood are currently being widely employed as a treatment for malaria, a protozoal blood disease. Wormwood has a long history of traditional use for treating parasitism but, again, little to nothing that proves it’s effective. We found nothing with a specific reference to dose or efficacy in horses.
We did find out that different species of wormwood may vary considerably in their activity. One, Artemisia absinthe, can be highly toxic to the nervous system. Essential oils from this variety have been shown to be highly effective when applied directly to insects such as mites, but the chemical responsible for this activity, thujone, causes toxicity.
Again, despite so many claims that Artemisia will remove worms, there are no strong research studies to support this claim.
Clove: Cloves and clove oil are commonly recommended ingredients in alternative dewormers, as they’re specifically claimed to have high activity against parasite eggs. However, justification for this claim is lacking. Cloves, and other aromatic spices, do contain high concentrations of a chemical called eugenol, which is an effective insecticide when sprayed directly onto bugs and vegetable worms in high concentration. However, as with garlic, whether this translates into an effect when small amounts are eaten and greatly diluted in the intestinal contents remains to be seen.
Pumpkin Seeds: Pumpkin seeds were a common parasite remedy in the late 1800s and early 1900s.?? They contain a substance called curcurbitin, which does have antiparasite activity in the lab.??However, traditional human dose is 200 to 400 grams, followed by a castor oil purgative “chaser.”
We’d like to believe alternative deworming remedies could have some truth to them, but we could find nothing solid to substantiate effectiveness or required dosages. Plus, the potential for toxicity is a real concern.
On the other hand, modern paste dewormer drugs have a proven high efficacy, and most are safe at 20 to 100 times the required dose. The days of scary, toxic chemical dewormers, like the organophosphates, are long gone. We see no reason to settle for less than high efficacy in dewormers, especially just to hang a “natural” label on the product.
While you may get away with them in a mature, healthy horse, we do not recommend experimenting with an alternative dewormer in young or aged horses, as these animals are far too susceptible to serious parasite-related problems.