Parasites are becoming resistant because dewormers have been used too often and not always strategically. The best way forward is targeted deworming based on fecal testing, plus good pasture management to reduce reinfection.
Key Takeaways
-
Parasite resistance is real and it’s making common dewormers less effective over time.
-
Overuse and incorrect deworming schedules are major drivers of resistance.
-
Fecal Egg Count (FEC) testing helps you deworm smarter, not more often.
-
Targeted deworming + pasture cleanup lowers parasite pressure without overusing medications.
-
Work with your vet to build a plan that fits your horse and your farm.
Are you concerned about the increasing ineffectiveness of deworming medications for horses? You’re not alone! Many of us feel the exact same way.
It’s undeniable that horse owners and veterinarians across the United States face a rising challenge: parasites in horses are developing resistance to commonly used deworming drugs.
This resistance complicates horse health management and raises questions about how to protect horses from debilitating parasites.
Understanding why this resistance is growing, how it affects horses, and what you can do as an owner to manage it, is crucial for the future of equine health.
The Growing Problem of Parasite Resistance in Horses
Parasite resistance happens when parasites survive despite the use of deworming drugs, passing on their resistance genes to their offspring. Over time, these resistant populations grow, making deworming drugs less effective.
Parasite resistance has been observed in many animals, including horses. A once-effective treatment now requires a more tailored approach.
The result is an urgent need for new strategies to manage horse parasites effectively without further promoting resistance.
Understanding Parasites in Horses
Horses are primarily affected by internal parasites like strongyles (large and small), ascarids, and tapeworms. These parasites can cause severe health problems, including colic, weight loss, and anemia, and, in some cases, they may be fatal if left unchecked.
Parasites reproduce in large numbers, often making frequent contact with deworming agents.
This frequency of exposure is one reason why parasites have developed resistance to certain drugs.
Why Deworming Is Essential for Equine Health
Effective deworming not only keeps individual horses healthy but also prevents the spread of parasites within herds and on properties.
Proper deworming can manage the health of both working and recreational horses by reducing the impact of these parasites on their digestive and immune systems.
Why Parasite Resistance to Deworming Medications Is Increasing Due To the following:
1. Overuse of Deworming Medications
One primary reason for the rise in resistance is the routine overuse of deworming drugs. Decades of consistent deworming practices have put intense selective pressure on parasites, leading to strains that can withstand the drugs intended to eliminate them.
2. Incorrect Deworming Practices
Using the wrong dosage or timing can inadvertently lead to resistance. For instance, deworming too frequently or deworming all horses at the same time without considering their individual parasite loads can promote the survival of resistant strains.
3. Limited Deworming Drugs Available
There are few classes of deworming drugs available for horses, such as macrocyclic lactones (e.g., ivermectin) and benzimidazoles. These limited options mean that once resistance develops to a particular class, alternatives are limited. This makes the rotation of different drug classes and timing even more essential.
Signs of Deworming Resistance in Horses
One of the key indicators of resistance is a lack of effectiveness in reducing parasite burdens after treatment. When a horse is dewormed but fecal egg counts remain high, it suggests the parasites may be resistant.
Health problems like weight loss, dull coat, poor stamina, or a proneness to colic may hint at an underlying parasite problem that has not been resolved by deworming, potentially due to resistance.
Current Strategies to Manage and Prevent Parasite Resistance
So, how can we help our equine friends get rid of these pesky invaders? Knowledge is power, so let the facts below keep you armed and ready against any and all pony-loving parasites.
1. Fecal Egg Count Testing
Veterinarians now recommend using fecal egg count (FEC) testing to monitor and determine each horse’s parasite load. By measuring the number of parasite eggs in a sample of manure, FEC tests guide targeted deworming, identifying which horses need treatment and when.
2. Strategic Deworming Programs
Rather than treating all horses on a set schedule, strategic deworming focuses on horses with high parasite burdens. Deworming only those that need it helps prevent resistance by reducing overall drug exposure.
3. Pasture Management
Rotating pastures, picking up manure (hello, Paddock Blade!), and avoiding overcrowding will help minimize parasite transmission on horse properties. Lowering the parasite load in the environment means horses are less likely to pick up new infections.
4. Rotational Deworming with Caution
Rotating between different classes of dewormers, while previously recommended, is now approached with more caution. If resistance to one class is present, switching to another drug is not always a solution and can sometimes accelerate resistance if not done strategically.
Always, always, always talk to your vet!
Informed Owners = Happy Horses
The rise in parasite resistance to deworming drugs in horses is a serious concern that requires a balanced, informed approach. By staying vigilant, using fecal egg count testing, and implementing pasture management practices with tools like Paddock Blade, horse owners can help control parasites while preserving the efficacy of deworming medications.
Taking these steps can ensure horses remain healthy and resilient, even as the landscape of parasite management continues to evolve.
Frequently Asked Questions:
1. How do I know if my horse has parasite resistance?
Fecal egg count testing is the best tool. If egg counts stay high after deworming, talk to your vet about possible resistance.
2. How often should horses be dewormed?
It depends on the horse and the environment. Many vets recommend targeted deworming based on FEC results rather than a fixed schedule.
3. Can parasite resistance be reversed?
No. Once resistance is established, it can’t be reversed—but it can be managed by reducing unnecessary deworming and improving parasite control strategies.
4. What’s the biggest mistake horse owners make with deworming?
Deworming too often without testing first. Overuse is one of the fastest ways to encourage resistance.
5. Does manure removal really help with parasite control?
Yes. Removing manure reduces parasite contamination in turnout areas, which lowers reinfection pressure and supports your overall parasite management plan.
TL;DR
Deworming medications are losing effectiveness because parasites are adapting. Use fecal egg counts, deworm only when needed, and reduce parasite exposure through manure removal, pasture rotation, and avoiding overcrowding.
