What Exactly Is Diatomaceous Earth?

Diatomaceous earth (DE) is a chalk-like powder created from the fossilized shells of microscopic algae called diatoms. These shells are made of amorphous silica, giving DE an abrasive, highly porous texture. Thanks to this structure, people have long used DE in products as diverse as filtration media, toothpaste polish, and an anti-caking aid in livestock feeds. A concise scientific overview is available on Wikipedia’s entry on diatomaceous earth.

Why Horse Owners Became Interested in DE

Over the last two decades, natural health forums and farm supply catalogs have promoted DE as a “chemical-free” dewormer. The idea is simple: when parasites inside the gastrointestinal tract brush against DE’s microscopic edges, their protective cuticles allegedly sustain sharp lacerations, causing dehydration and death. Advocates often sprinkle food-grade diatomaceous earth onto grain or top-dress it on hay, hoping to mimic DE’s well-documented ability to desiccate insects externally.

How DE Is Supposed to Work in the Equine Gut

Externally, DE works because small insects have thin exoskeletons. When they crawl through a dusting of DE, the abrasive silica scratches their waxy coating, and they lose moisture until they die. Internal parasites, however, dwell in a vastly different environment—warm, moist, and turbulent. To damage a parasite inside a horse, DE particles would have to:

• Survive the soaking process of chewing, salivation, and stomach acid.
• Remain in high enough concentration across 100+ feet of intestinal surface.
• Physically contact parasites despite layers of digesta and mucus.

That chain of events is theoretically weak, and modern research tests have borne this out.

What Peer-Reviewed Studies Actually Show

The most often cited equine study was conducted at Texas A&M University. Thirty-seven horses on a single ranch were divided into control and treatment groups. Over several weeks the treatment group received DE mixed into their feed at manufacturer-recommended rates. Fecal egg counts were taken multiple times. The outcome, published on ProEquineGrooms, showed no statistically significant reduction in strongyle or ascarid egg counts. In plain language, the product performed no better than leaving the horses untreated.

Additional trials abroad and in smaller university herds have reached identical conclusions—none have demonstrated a noteworthy anthelmintic effect from DE in horses. Importantly, the lack of efficacy was consistent across different brands and feeding rates.

Expert Opinions From Leading Parasitologists

Dr. Martin K. Nielsen, a world-recognized equine parasitologist at the University of Kentucky’s Gluck Equine Research Center, often fields DE questions at conferences. In a 2018 interview with Equus Magazine, Dr. Nielsen noted two critical points:

First, even if DE could damage parasites, the abrasive particles would be dramatically diluted inside a bolus of ingesta. Second, if those particles were sharp enough to shred worms, they could just as easily abrade the horse’s intestinal lining—a trade-off no responsible caretaker should accept.

Potential Benefits of DE Outside Deworming

Although DE falls short as an internal parasite control, it still has legitimate uses around the stable:

Anti-caking agent in feed: Agricultural feed companies have long added small amounts of DE to pelleted rations to prevent clumping. At the 1–2 % inclusion rate, DE keeps minerals from bridging and improves flow in automatic feeders. When used this way, the product is classified as “Generally Recognized As Safe” by the U.S. FDA.

Fly and crawling insect control: Sprinkling DE insect control powders along stall edges can reduce darkling beetles, roaches, and ants. Results are especially noticeable in feed rooms, where moisture levels are low enough for DE to stay dry and effective.

Odor management: The same porosity that desiccates insects can trap ammonia molecules. Lightly dusting soiled bedding before adding fresh shavings can keep stalls smelling cleaner between pick-outs.

Safety Considerations and Proper Handling

Silica dust—including DE—should be respected. The crystalline form of silica is recognized as a respiratory hazard, but food-grade DE is overwhelmingly composed of amorphous silica, which is less dangerous. Even so, prolonged inhalation can still irritate lungs and eyes. The following precautions keep your horses, and you, safe:

• Use a simple dust mask and goggles when applying DE in confined areas.
• Avoid dumping large amounts from shoulder height; instead, scoop close to the bedding surface to limit airborne clouds.

In our own 20-stall barn, switching to a handheld flour sifter reduced visible airborne particles by half and kept neighboring tack cleaner.

Integrating DE Into a Modern Parasite Control Program

The risk of untreated parasite burdens—colic, weight loss, and permanent intestinal damage—far outweighs the convenience of a single “natural” powder. A veterinarian-directed protocol balances three strategies:

1) Fecal Egg Counts (FECs) every 8–12 weeks to map individual shedders.
2) Targeted deworming with proven chemical classes such as macrocyclic lactones, benzimidazoles, and pyrimidines.
3) Pasture management. Rotational grazing, manure collection in high-traffic paddocks, and cross-species grazing with cattle or sheep can reduce larval contamination by up to 80 %.

Diatomaceous earth can supplement point three—applied to manure piles in summer, it dries fly larvae. Still, it should never replace chemical wormers for horses that demonstrate high FECs.

Real-World Barn Observations

During a Virginia heatwave last year, our farm experimented with DE sprinkled on manure piles awaiting the spreader. Within 48 hours, maggot activity plummeted. Yet FECs taken from the same horses a week later remained unchanged, illustrating the dual reality: DE can be useful environmentally while being ineffective internally.

How Much DE Is Usually Fed?

Manufacturers typically recommend 1 cup (approximately 80 grams) per 1,000 lb horse. Because dosage questions are common, the short video below demonstrates measuring techniques and palatability tips:

Key Takeaways for Horse Owners

• Diatomaceous earth for horses is valuable in feed bins and stall aisles, but peer-reviewed science shows no deworming benefit inside the gastrointestinal tract.
• Over-reliance on DE can delay effective treatment, potentially allowing colic-causing parasite loads to escalate.
• Discuss any supplement—including equine DE supplements—with your veterinarian so it complements, rather than sabotages, your strategic parasite-control plan.

Conclusion: A Balanced Perspective on Diatomaceous Earth for Horses

The popularity of diatomaceous earth for horses stems from a genuine desire to minimize synthetic chemicals. Unfortunately, good intentions cannot override biology. Studies from Texas A&M and other institutions, coupled with commentary from leaders such as Dr. Nielsen, confirm that DE does not act as an internal dewormer. Still, dismissing DE entirely would be a mistake; its absorbent, abrasive nature can enhance stable hygiene and feed flow when used correctly.

Ultimately, the safest and most cost-effective parasite program relies on diagnostic testing, evidence-based dewormers, and smart pasture maintenance. View diatomaceous earth as a peripheral tool—useful for moisture control and insect suppression—but not as the frontline defense against internal equine parasites. When in doubt, partner with your veterinarian and let data, not anecdotes, direct your horse-care decisions.