Parasite control is a critical aspect of equine health, but over time, the way we approach deworming has evolved. Many horse owners continue to follow traditional practices, deworming their horses regularly without understanding the nuances of modern equine parasite management.
But is this approach still relevant today? Increasing evidence suggests that many horse owners may be deworming their horses too often, leading to negative consequences like drug resistance in parasites.
In this blog, we’ll explore why excessive deworming can be harmful, discuss updated strategies for parasite management, and look at alternatives to frequent deworming.
The Evolution of Deworming Practices
Historically, the standard approach to parasite control was to deworm horses on a routine schedule, often every 6 to 8 weeks. This practice was based on the assumption that horses constantly carried significant parasite loads that required frequent treatment. While well-intentioned, this method was not based on scientific evidence but rather on the availability of commercial anthelmintics (dewormers) starting in the 1960s and 70s.
Recent studies, however, reveal that this traditional approach is not only outdated but also contributes to the development of drug-resistant parasites.
According to research published in the Journal of Equine Veterinary Science (2019), over-reliance on deworming products has led to a rise in resistant parasites, particularly small strongyles, the most common internal parasite in adult horses today.
The Problem of Dewormer Resistance
One of the primary concerns with frequent deworming is the development of resistance. As parasites are exposed to dewormers, they can gradually adapt and evolve to withstand the effects of these drugs. The result is that once-effective dewormers lose their efficacy, making it harder to control parasites and protect horse health.
A study conducted by Dr. Martin Nielsen, an equine parasitologist at the University of Kentucky, found that more than 80% of horse farms had evidence of dewormer resistance, particularly to fenbendazole and pyrantel pamoate, two commonly used deworming agents. He notes that “routine, rotational deworming is no longer a viable strategy due to the widespread resistance we’ve observed in equine parasites.” This resistance is a growing problem, and horse owners need to adapt their parasite management strategies accordingly.
Are You Deworming Your Horse Too Often?
Many horse owners continue to deworm their horses on a regular schedule, often every two months, as part of a routine care plan. However, research shows that many horses do not need to be dewormed this frequently. In fact, in a well-managed environment, only a small percentage of horses carry a heavy parasite load that warrants frequent treatment.
Dr. Craig Reinemeyer, a renowned equine parasitologist and researcher, explains that approximately 20% of horses carry 80% of the total parasite burden in a herd. This means that most horses do not require frequent deworming, and doing so can contribute to unnecessary drug use and the development of resistance.
Studies have demonstrated that targeted deworming, also known as “strategic deworming” or “selective deworming,” is a far more effective approach. By identifying the horses that carry significant parasite loads and deworming only those individuals, owners can reduce overall dewormer use while maintaining effective parasite control.
Fecal Egg Count (FEC) Testing: The Key to Strategic Deworming
One of the most significant advancements in equine parasite control is the use of fecal egg count (FEC) testing. FEC tests measure the number of parasite eggs present in a horse’s manure, providing a clear picture of the animal’s parasite burden. By performing FEC tests regularly, horse owners and veterinarians can determine which horses need treatment and which do not.
FEC testing allows for a more individualized approach to deworming, reducing the need for blanket treatments. Horses with low fecal egg counts (FECs) may not need deworming at all, while horses with high counts can be treated appropriately.
Studies show that FEC-guided deworming can significantly reduce the frequency of treatments without compromising horse health. In fact, a study published in the Equine Veterinary Journal found that targeted deworming reduced anthelmintic use by up to 80%, while maintaining effective control of parasite populations.
How Often Should You Deworm?
The frequency of deworming should be based on the results of FEC testing and the individual horse’s parasite burden.
In general:
Low Shedders: Horses with consistently low fecal egg counts (under 200 eggs per gram, or EPG) may only need to be dewormed once or twice a year.
Moderate Shedders: Horses with FECs between 200 and 500 EPG may require deworming 2-3 times per year.
High Shedders: Horses with FECs over 500 EPG may need more frequent treatments, around 4 times per year, particularly during periods of high transmission (spring and fall).
It’s important to note that no deworming schedule is one-size-fits-all. The best plan for your horse will depend on their individual parasite load, as well as environmental factors such as pasture management, stocking density, and the presence of young horses, which are more susceptible to parasites.
Alternatives to Frequent Deworming
While deworming remains an important tool in parasite control, there are several non-chemical strategies that horse owners can implement to reduce parasite exposure and the need for frequent deworming. These alternatives, when combined with FEC testing, can significantly enhance parasite management without relying solely on anthelmintics.
1. Pasture Management
Effective pasture management is one of the best ways to reduce parasite exposure. Parasites like small strongyles and ascarids are spread through manure, so controlling manure in the pasture can help limit the spread of these parasites.
Regular manure removal: Removing manure from paddocks and pastures at least twice a week can drastically reduce the number of parasite larvae that your horse is exposed to. Studies suggest that pastures with regular manure removal have 50-90% fewer parasites.
Pasture rotation: Rotating horses between pastures allows time for parasite eggs and larvae to die off before horses are reintroduced. Parasite larvae typically require moist, warm conditions to survive, so leaving a pasture fallow for a few months, especially during hot, dry weather, can break the life cycle of many parasites.
2. Mixed Grazing
Another strategy to reduce parasite load is to graze horses alongside other livestock, such as sheep or cattle. Because the parasites that infect horses are different from those that infect sheep or cattle, grazing different species together can help interrupt the life cycle of equine parasites. This practice is supported by a study published in the Journal of Parasitology, which found that mixed grazing reduced the number of parasites in horses compared to horses grazing alone.
3. Targeted Deworming for Young Horses
Foals and young horses are more susceptible to certain parasites, such as ascarids (roundworms), which can cause serious health issues if left unchecked. In these cases, strategic deworming of young horses is essential to protect their health. However, this doesn’t mean treating them excessively. Instead, targeted treatments based on fecal egg counts and a knowledge of age-related parasite risk factors are the most effective.
For example, young horses should be monitored closely for ascarid infections through fecal testing, and treated appropriately if a high egg count is found. At the same time, mature horses often develop natural immunity to ascarids, meaning they don’t require the same level of treatment.
4. Utilizing Natural Supplements
Some horse owners have turned to natural supplements to support parasite control, although these should be used with caution. Herbal supplements such as garlic, diatomaceous earth, and pumpkin seeds are commonly promoted for their potential anti-parasitic properties. While anecdotal evidence exists, the scientific research supporting their efficacy is limited.
A study published in the Veterinary Parasitology Journal in 2020 evaluated the effect of garlic on equine parasites and found no significant reduction in fecal egg counts. As such, while natural supplements may play a role in supporting overall gut health, they should not replace traditional parasite control measures, such as FEC testing and targeted deworming.
Adapting to Modern Parasite Control
The days of routine, frequent deworming are over. Modern research shows that many horses do not need to be dewormed as often as once thought, and overuse of dewormers has led to the serious problem of drug-resistant parasites.
Instead, the best approach is to work with your veterinarian to develop a targeted parasite control program, using tools like fecal egg count testing and strategic deworming based on individual parasite burdens.
By implementing pasture management practices, utilizing FEC testing, and being judicious with dewormer use, you can protect your horse’s health while also reducing the risk of contributing to dewormer resistance.
Parasite control is no longer about how often you can deworm, but rather how smart you can be with your deworming strategy.
