Key Takeaways
- Fecal egg counts (FECs) are essential for targeted parasite control in horses
- Spring, summer, and fall are key testing periods in the US
- Not all horses require the same worming schedule—testing identifies high shedders
- Over-worming can lead to drug resistance and reduced effectiveness
- Good pasture management and regular testing work together to reduce parasite risk
Introduction
Parasite control is one of the most important aspects of horse health management, yet it’s also one of the most misunderstood. For years, routine deworming schedules were the norm—treating every horse every few months without question. But modern research has changed that approach dramatically.
Today, the focus has shifted toward targeted parasite control, and at the center of this strategy is the fecal egg count (FEC) test.
For horse owners across the United States, understanding when to do a fecal test—and how to use the results effectively—can make a significant difference in your horse’s health, your pasture quality, and even your long-term costs.
In this guide, we’ll break down exactly when to test, why timing matters, and how to get the most value from fecal testing throughout the year.
What Is a Fecal Egg Count and Why It Matters
A fecal egg count (FEC) is a laboratory test that measures the number of parasite eggs present in a horse’s manure. It provides a snapshot of how many adult worms are actively reproducing inside the horse.
Rather than guessing whether your horse needs deworming, an FEC allows you to make data-driven decisions.
Why this matters:
- Not all horses carry the same parasite load
- A small percentage of horses (often 20–30%) shed the majority of eggs
-
Blanket deworming contributes to parasite resistance, making treatments less effective over time
By using FEC testing, you can:
- Identify high shedders that need more frequent treatment
- Avoid unnecessary deworming in low-risk horses
- Protect the effectiveness of existing deworming medications
This shift toward targeted control is now considered best practice across the US equine industry.
When Should You Do a Fecal Test for Horses?
Timing is everything when it comes to fecal testing. Conducting tests at the right times of year ensures you get accurate results and can respond appropriately.
Spring (Primary Testing Period)
Spring is one of the most important times to perform a fecal egg count.
As temperatures rise, parasite larvae that survived the winter become active on pasture. Horses begin grazing more, increasing their exposure.
Testing in spring helps you:
- Assess parasite levels after winter
- Identify which horses are high shedders
- Plan your parasite control strategy for the grazing season
For most US regions, this means testing between March and May, depending on climate.
Summer (Monitoring Phase)
During summer, parasite transmission can remain high, especially in warm and humid regions.
A mid-season fecal test allows you to:
- Monitor whether parasite levels are increasing
-
Check if previous deworming treatments were effective
-
Adjust your management strategy if needed
In hotter, drier areas, parasite activity may slow slightly, but testing is still valuable for tracking trends.
Fall (Critical Control Period)
Fall is another key time to test and treat.
As grazing continues and conditions cool, parasite burdens can build up again. Testing during this period helps prepare horses for winter and reduces pasture contamination.
In many cases, fall testing is paired with:
- Targeted deworming
- Tapeworm treatment (if indicated)
This is typically done between September and November.
Winter (When Testing May Be Less Useful)
In colder climates, parasite activity slows significantly during winter. As a result, fecal egg counts may appear lower—not necessarily because the horse is parasite-free, but because worms are less active.
Testing in winter can still be useful in some cases, but it’s generally not considered a primary testing window.
Understanding Fecal Egg Count Results
Getting a fecal test is only half the equation—you also need to understand what the results mean.
FEC results are typically measured in eggs per gram (EPG).
General guidelines:
-
Low shedder: 0–200 EPG
-
Moderate shedder: 200–500 EPG
-
High shedder: 500+ EPG
These categories help determine how often a horse should be dewormed.
For example:
- Low shedders may only need treatment 1–2 times per year
- High shedders may require more frequent intervention
It’s important to work with your veterinarian to interpret results in the context of your horse’s age, health, and environment.
Fecal Egg Count Reduction Tests (FECRT)
Another important tool is the fecal egg count reduction test (FECRT).
This involves:
-
Performing a fecal test
-
Administering a dewormer
-
Testing again 10–14 days later
The goal is to measure how effective the treatment was.
Why this matters:
-
It helps detect dewormer resistance
-
Ensures you’re using products that actually work
-
Prevents wasted time and money on ineffective treatments
Resistance is an increasing problem in the US, particularly with small strongyles, making FECRT an essential part of modern parasite control.
Factors That Influence When to Test
While general timing guidelines are helpful, several factors can influence when and how often you should test.
Geographic Location
The US has a wide range of climates, from humid Southeast regions to arid Western states. Parasite activity varies accordingly.
- Warm, humid areas → higher parasite pressure
- Cold regions → shorter parasite seasons
Horse Age
Younger horses are more susceptible to parasites, particularly roundworms.
- Foals and yearlings may require more frequent monitoring
- Adult horses often develop partial immunity
Pasture Management
Your paddock setup plays a major role in parasite exposure.
Higher risk conditions include:
- Overstocked pastures
- Poor manure management
- Continuous grazing without rotation
Better-managed environments can significantly reduce parasite load.
Tips for Getting Accurate Fecal Test Results
To get the most reliable results from a fecal test, it’s important to follow proper collection and handling procedures.
Best Practices:
- Collect a fresh manure sample (ideally within a few hours)
- Use clean gloves and a sealed container
- Avoid contamination with soil or bedding
- Keep the sample cool, but do not freeze it
- Deliver to your vet or lab as soon as possible
Timing also matters—avoid testing immediately after deworming, as results may not reflect the true parasite burden.
Integrating Fecal Testing with Paddock Management
Fecal testing is most effective when combined with good pasture management practices.
Key strategies include:
- Regular manure removal (at least twice weekly)
- Rotational grazing to break parasite life cycles
- Avoiding overstocking
- Cross-grazing with other species (where possible)
These approaches reduce the number of infective larvae on pasture, lowering the overall parasite challenge for your horses.
Conclusion
Fecal egg count testing has transformed how horse owners approach parasite control. Instead of relying on outdated, one-size-fits-all deworming schedules, today’s best practice is targeted, evidence-based management.
By understanding when to do a fecal test—and using the results effectively—you can protect your horse’s health, reduce unnecessary treatments, and help combat the growing issue of parasite resistance.
In the US, the key testing windows—spring, summer, and fall—provide a structured approach to monitoring and managing parasite burden throughout the year.
Ultimately, fecal testing isn’t just about worms. It’s about making smarter decisions, improving long-term outcomes, and maintaining a healthier environment for your horses.
FAQs
1. How often should I do a fecal test on my horse?
Most horses benefit from testing 2–3 times per year, typically in spring, summer, and fall.
2. Do all horses need to be dewormed after a fecal test?
No. Only horses with moderate to high egg counts typically require treatment.
3. Can I do a fecal test at home?
Some kits are available, but lab testing through a veterinarian is more accurate.
4. What is a high egg count in horses?
Generally, anything over 500 eggs per gram (EPG) is considered high.
5. Why is over-worming a problem?
Overuse of dewormers can lead to parasite resistance, making treatments less effective over time.
TL;DR
Fecal egg counts (FECs) help horse owners make smarter parasite control decisions. In the US, testing in spring, summer, and fall allows you to identify high shedders, avoid unnecessary deworming, and reduce resistance. Combined with good pasture management, fecal testing is the most effective way to maintain horse health and control parasites long-term.
