A Veterinarian’s Perspective: Why I No Longer Rely Solely on Ivermectin for Horse Deworming

Veterinarian perspective provided by Dr. Paul E. Clemens, Owner and Principal Veterinarian, Auburn Animal Care in Geauga, Ohio.

This article shares a veterinarian-informed perspective on how horse deworming is changing, including the role of ivermectin, parasite resistance, fecal egg count testing, pasture ecology, and natural parasite support.

Quick Summary

• Ivermectin has long been used as a common horse dewormer, but routine chemical deworming is no longer the only approach many veterinarians recommend.
• Parasite resistance is a growing concern, especially when horses are dewormed on a fixed schedule without testing.
• Modern equine parasite management often uses fecal egg count testing to better understand parasite load and treatment needs.
• Chemical dewormers may also affect pasture ecology, including beneficial dung beetles that help break down manure.
• A balanced horse deworming strategy may include fecal testing, pasture management, manure control, veterinary guidance, and natural parasite support.
• Natural horse deworming should not mean ignoring parasites. It should be part of a responsible, observation-based care routine.

Why My Approach to Horse Deworming Changed

For decades, chemical dewormers like ivermectin were considered the foundation of equine parasite control. Like many horse owners, I followed traditional rotational deworming schedules because that was simply the accepted standard throughout much of the horse industry.

But over time, after studying modern parasite research, resistance trends, pasture ecology, and natural alternatives alongside veterinarians who specialize in equine health, my philosophy toward parasite management began to change.

What I learned is that effective parasite control is far more complex than simply eliminating worms on a schedule.

Horses naturally encounter intestinal parasites while grazing. Low levels of parasitism may exist without causing disease in otherwise healthy horses. At the same time, parasite burdens can become severe and, in some cases, even life-threatening. Proper parasite management remains an important part of responsible equine care.

The goal, however, is not necessarily to create a completely parasite-free horse at all times. The goal is to maintain balance, minimize harmful parasite burdens, and support long-term equine health without unnecessarily disrupting the horse or the surrounding pasture ecosystem.

That shift in understanding is one of the primary reasons I no longer rely solely on ivermectin or routine chemical dewormers as my only approach to horse parasite management.

The Growing Problem of Parasite Resistance in Horses

One of the biggest factors influencing my thinking was learning more about anthelmintic resistance.

For decades, many horses were routinely dewormed every few months regardless of actual parasite load. Over time, repeated exposure to the same chemical compounds has allowed certain parasites to adapt and survive treatment.

Today, resistance among equine parasites is being reported with increasing frequency worldwide. Several common equine parasites—including small strongyles, also known as cyathostomins, and ascarids—have demonstrated resistance to multiple classes of conventional dewormers. Cases of reduced effectiveness and even complete treatment failure have been documented in some areas. Resistance concerns have also been reported involving equine pinworms and tapeworms.

Because of this, many veterinarians and modern parasite-control guidelines have shifted away from blind rotational deworming schedules toward more strategic, surveillance-based approaches. The American Association of Equine Practitioners recommends fecal egg count testing and strategic parasite control rather than fixed-interval, year-round deworming.

That often includes:

• Fecal egg count testing
• Identification of parasite species
• Monitoring regional resistance trends
• Evaluating pasture conditions and stocking density
• Strategic treatment when appropriate
• Ongoing veterinary consultation

The concern is simple: when parasites are repeatedly exposed to the same chemical compounds, the strongest survivors remain and continue reproducing. Eventually, the effectiveness of those products may diminish.

This evolving science was a major turning point for me personally.

Why Fecal Egg Counts Matter in Modern Horse Deworming

Modern horse deworming is no longer just about giving a product on a calendar. Fecal egg count testing can help determine whether a horse is a low, medium, or high shedder and whether parasite-control decisions should be adjusted. 

This does not mean fecal testing tells the whole story. Some parasite stages may not show clearly in a fecal test, and a veterinarian should still help interpret results and recommend a complete parasite-control strategy.

But fecal testing gives horse owners and veterinarians a better way to make informed decisions instead of treating every horse the same way, every few months, regardless of actual need.

For many horses, this more strategic approach may reduce unnecessary chemical exposure while still keeping parasite control active and responsible.

The Hidden Environmental Cost of Chemical Dewormers

Another eye-opener was learning how chemical dewormers may affect beneficial organisms within horse pastures, especially dung beetles.

Most horse owners do not think much about dung beetles, but they play an important role in maintaining healthy grazing environments. These insects naturally break down and bury manure piles, helping:

• Reduce manure accumulation
• Improve soil health
• Support nutrient cycling
• Reduce fly populations
• Promote cleaner grazing areas
• Potentially lower environmental parasite exposure

The concern is that residues from chemical dewormers like ivermectin can pass through the horse and remain active in manure after treatment. Research on ivermectin residues has shown potential impacts on dung beetle communities, dung degradation, and soil properties.

When dung beetle populations decline, manure may remain in the pasture longer. That can create larger breeding grounds for flies and allow parasite eggs and larvae to persist in grazing areas for longer periods of time.

Ironically, some of the very products designed to control parasites may also disrupt part of nature’s own pasture-cleaning system.

A More Balanced and Natural Approach to Horse Deworming

As I continued studying equine health, pasture ecology, and natural alternatives with veterinary guidance, I became increasingly interested in approaches that work more holistically alongside the horse rather than relying exclusively on repeated chemical intervention.

Natural products such as Atlas Natural Horse Dewormer offer a non-chemical approach to parasite management that some horse owners choose to incorporate as part of a broader parasite-control strategy.

Rather than relying only on a single chemical mode of action, many natural formulations use multiple ingredients and support strategies that may appeal to horse owners looking for a more balanced approach. For many owners, the goal is not to ignore parasites, but to support the horse while also being thoughtful about resistance, pasture health, and long-term management.

Natural approaches may also complement broader wellness-focused practices aimed at supporting:

• Digestive health
• Internal balance
• Immune resilience
• Nutrient absorption
• Overall vitality and condition

For me, the philosophy became less about constantly trying to chemically sterilize the horse’s digestive system and more about supporting healthy horses, healthy pastures, and responsible long-term care.

Natural Support Works Best With Responsible Management

Choosing a more natural philosophy still requires responsible parasite management and ongoing veterinary care.

In fact, responsible parasite management still requires:

• Regular fecal egg count monitoring
• Proper manure management
• Rotational grazing
• Avoiding overstocked pastures
• Monitoring horse condition and health
• Strategic intervention when necessary
• Ongoing veterinary consultation

No single product, natural or chemical, should replace good management practices.

Chemical dewormers still have a place in certain situations. Severe parasite burdens and high-risk cases may require targeted conventional treatment. But after learning more about resistance development, pasture ecology, and the long-term effects of repeated chemical exposure, I personally no longer believe that routine chemical deworming should automatically be the first and only line of defense.

A Different Philosophy of Horse Care

Today, I believe effective parasite management is about balance, observation, science, and stewardship.

Healthy horses begin with healthy systems:

• Healthy digestion
• Healthy immune function
• Healthy grazing environments
• Responsible pasture management
• Strategic parasite monitoring

Modern equine parasite science continues to evolve, and my approach evolved with it.

That is why I no longer rely solely on ivermectin or routine chemical dewormers as my only strategy for protecting equine health.

The better path is not fear. It is informed, consistent, responsible care that considers the horse, the pasture, and the long-term health of both.

Frequently Asked Questions About Ivermectin and Natural Horse Deworming

Is ivermectin still used for horse deworming?

Yes. Ivermectin is still widely used in equine parasite control and may be appropriate in certain situations. The concern is not that ivermectin has no place. The concern is relying on routine, repeated use without testing, monitoring, or veterinary guidance.

Why are some horse owners moving away from routine ivermectin use?

Many horse owners and veterinarians are paying closer attention to parasite resistance, fecal egg count testing, and pasture ecology. Routine deworming on a fixed calendar may not be the best strategy for every horse or every property.

What is parasite resistance in horses?

Parasite resistance happens when parasites survive exposure to a deworming product and continue reproducing. Over time, repeated use of the same type of dewormer can make that product less effective against certain parasite populations.

What is a fecal egg count?

A fecal egg count is a test that measures the number of parasite eggs in a manure sample. It helps veterinarians and horse owners better understand parasite shedding levels and make more strategic deworming decisions.

Can natural horse dewormers replace chemical dewormers?

Not always. Natural horse dewormers may be used as part of a broader parasite-management strategy, but they should not replace veterinary care, fecal testing, pasture management, or targeted treatment when a horse has a serious parasite burden.

How can I support parasite control naturally?

Natural parasite support may include manure management, rotational grazing, avoiding overcrowded pastures, monitoring body condition, supporting digestive health, using fecal egg counts, and working with a veterinarian to determine the best approach for each horse.