Chances are, your healthy adult horse might fend off some worms himself.

The control of internal parasites is a major equine health issue. Concerns about regular exposure to deworming chemicals and dewormer resistance in parasites often lead owners to consider the use of natural dewormer products. Understandable, yes, but before you put anything into your horse’s body, whether it carries a claim of natural or not, you should ask yourself two questions. Is it safe? Does it work?

Safety And Dosage
Safety concerns are a major issue that drives people to investigate natural products, but of all the natural approaches you could take, herbal deworming is the most potentially toxic, if you use effective dosages. The effectiveness of herbal dewormer ingredients is also directly proportional to their toxicity.

Three of the most potent are Wormwood (Artemisia absinthium), Wormseed (Chenopodium ambrosdioides) and Male Fern (Dryopteris filix). They share nervous-system toxicity as well as potential damage to other organs. The line between an effective dose and a toxic or even lethal one is so fine that even at usual dosages more sensitive animals can show toxicity. Veterinary texts from "back in the day" do note use of these ingredients but also record significant toxicities and even deaths. Another ingredient of significant concern is Black Walnut. Feeding any portion of the Black Walnut tree to a horse is flirting with laminitis.

Pumpkin seeds contain a chemical that is effective as a dewormer, but tremendous amounts have to be ingested to get the effect. The effective dose for an adult human is as much as a pound of the seeds.

Consider This...
• Pumpkin seeds might work for deworming a horse, but he’d have to consume 5 to 10 lbs. of them at once. • The popular natural dewormer diatomaceous earth won’t work in a wet environment, like the horse’s digestive tract. • Traditional deworming pastes are proven and economical. • Most healthy adult horses can get by with less deworming overall, except in high-exposure situations.

Considering the larger volume of the equine intestinal tract, an equivalent dose of five to 10 pounds is reasonable. However, even if the horse would eat all that, it may well cause considerable gut upset itself.

A variety of other aromatic herbs—including clover, anise, fennel, sage and garlic—have been suggested and are safe in reasonable amounts but effects, if any, are small.

Diatomaceous earth (DE) is often suggested. This is a finely ground powder that contains the fossilized skeletons of small organisms called diatoms. These skeletons are razor sharp at the microscopic level. Diatomaceous earth can cut and kill a variety of soft-bodied pests, including slugs and insect or parasite larvae, but there’s a catch. It doesn’t work when it’s wet. The intestinal tract of a horse is a wet environment. The fine powder is also a respiratory irritant and when fed dry it may irritate the mouth if the horse is not producing a generous amount of saliva. As manure dries out, it’s possible the DE could be doing some damage to emerging larvae but drying alone does a good job.

To summarize, there is no reason to expect diatomaceous earth orally would have any effect and, while several natural plant materials do have antiparasite activity, there is a very narrow margin of safety. If you give these products and have no side effects, odds are there’s not enough in there to hurt the parasites either.

Tobacco

The myth that tobacco is a good choice remains alive and well. We found a letter that suggested feeding a wormy horse an ounce of snuff, tying the horse up and waiting an hour, at which point the horse would pass "stomach worms." The problem with this scenario is that the tobacco wouldn’t have enough time to reach any area of the intestine where parasites reside, let alone have an effect on them. What’s more likely going on is stimulated intestinal motility. Tobacco toxicity causes nausea, but since horses can’t vomit the tobacco will pass into the small intestine and be absorbed. At that point, the horse will be stimulated to pass manure. Overdo it, and nervous system or cardiac effects will also result.

Proof Not Positive
You’ve probably heard testimonials from people who are using these products and say their horses always have negative fecal results. That would make you think the products work. Testimonials are valuable as a starting point, but they don’t prove much. The fact of the matter is that most adult horses have a strong immunity to parasites and will run low or negative fecal egg counts if properly managed. This includes:

• Turnout on pasture sufficient to support the number of horses without overgrazing.
• Closed herd, or isolation and deworming prior to herd introduction with new horses.
• Daily to twice daily removal of manure from stalls, paddocks and crowded fields.
• Minimize stress and maximize nutrition to support health in general, including the immune system.
• Do not feed hay or grain from the ground in stalls or crowded areas.
• Use concrete and/or cleanable mats in outside feeding areas and keep them dry.
• Use lime or other stall-drying products to absorb moisture from urine and water spills in stalls.

Is it possible that the testimonials are correct and nontoxic levels of natural dewormers are keeping parasites at bay? Yes, but we need a real study done in an organized fashion.

We asked the manufacturers/distributors of the natural deworming products in our chart if they had any research to back up their products. We weren’t looking for anything complicated, just before and after fecal checks to see if the products worked. The list of companies we contacted, a description of their products, and their replies are in our chart.

Bottom Line
It’s a no-brainer in our opinion: Given the lower price, low potential for toxicity and proven effectiveness of paste dewormers, compared to no data available on effectiveness and safety of alternative dewormers, we think the choice is obvious. Properly maintained healthy adult horses may not need deworming at all. If you’re concerned with resistance, consider doing periodic fecal egg counts. Until there’s solid information, we’ll pass on natural dewormers.