Fecal Egg Counts and Parasite Management Plans

What is a Fecal Egg Count (FEC)?

FEC is a quantitative assessment of internal parasite eggs shed by your horse in its manure.  A measured volume of manure is mixed with a flotation solution and evaluated on a specially calibrated microscope slide.  This allows us to calculate the number of parasite eggs per gram of manure.

The current recommendation is to deworm based off fecal egg counts rather than an every other month rotation.  FEC’s are useful to determine:

  • Which dewormers are effective on a particular farm
  • Which horses are high vs low shedders by nature (creating a customized parasite management program for your horse)
  • The interval between dewormers that is required (decreasing unnecessary chemicals in our horses when they don’t need it)
  •  If parasite resistance is developing on a farm (monitoring trends to see if resistance is developing or going away)


Why Do Some Horses Shed More Eggs Than Others?

Horses on the same pasture or management plan may be found to consistently have very different amounts of internal parasite eggs in the manure.  Approximately 20% of horses will carry 80% of the parasites on most farms!

All horses are exposed to parasites throughout their life.  They develop varying levels of intestinal immunity which allows them to hold adult intestinal parasites in check.  

The immune systems of young horses (<3yrs) and aged horses are less able to adapt to and hold intestinal parasites at low levels.


What is a High, Medium, or Low Shedder?

Adult healthy horses consistently carry similar worm burdens through the year, which allows us to customize parasite management plans based on the level of intestinal parasite eggs that they are shedding.

High Shedding horses will need more frequent strategic deworming, compared to Medium or Low shedders.

This allows us to decrease unnecessary use of dewormers by using them strategically in the horses with less natural immunity to intestinal parasites

Henderson Equine Clinic recommends a Fecal Egg Count be performed every Spring (April/May) and Fall (October/November) to assess your horse’s parasite burden/shedding status and to allow us to create a customized Parasite Management Program.  

Follow up Fecal Egg Counts may need to be performed at specific times throughout the year depending on your parasite management program.

What else can we do to control Parasites on farm?
In our area, the highest risk for parasite eggs on pasture is May/June through October.


Techniques for Pasture Management:

  • Don't overstock your pastures (over grazed pastures increase ingestion of parasite eggs)
  • Regularly dispose of manure and don't spread onto pastures currently being grazed
  • Drag/harrow paddocks to break up manure piles and leave open for 2-3 weeks
  • Use feeders for hay or grain rather than feeding off the ground
  • Keep foals and weanlings separate from yearlings to help prevent ascarid infections


Why do we care about changing the way we deworm?

     Across the country, all types of horse farms have reported resistance to certain dewormer classes.  The most commonly reported resistance is to fenbendazole and ivermectin products.  There are very few new deworming drugs being developed (and none for horses).  Our goal is to use the options we have intelligently to minimize the further development of parasite resistance. Many serious conditions have been almost eliminated by modern deworming programs and we would like to keep it that way.  New deworming and Fecal Egg Count recommendations are aimed at achieving this by focusing on individual horses.


Henderson Equine Clinic's Deworming Recommendations

Collect and submit a fecal sample on each horse (or a grouped sample on horses kept in large groups) in the spring (March/April) and fall.

  • For each horse to be tested a fecal sample is submitted BEFORE to deworming. 
  • To collect a fecal sample:

1.  Collect 2 fecal balls of manure ideally passed within 1-2 hours but definitely less than 24 hours
2.  Place the manure in a plastic ziplock bag, removing all air possible
3.  Store the sample in a refrigerator until it can be picked up or delivered to the clinic.

You will receive a custom Parasite Management Plan for each horse (or group). 

  • Most low shedding horses will have Fecal Egg Counts and be treated biannually (early spring and fall)
  • Moderate and high shedding horses will need additional deworming and strategic Fecal Egg Count Assessments during times of highest parasite risk.
  • Foals and Senior horses will require different strategic deworming programs than mature horses.

Once per year a Fecal Egg Count Reduction should be performed on atleast one horse on your farm.

  • Submit a fecal sample just prior to deworming and ten days to two weeks after deworming depending on dewormer used.
  • Comparing the Fecal Egg Count results from just prior to deworming to those two weeks after deworming provides a quantitative measure of resistance.  These results will help determine if this deworming product is effective on your property and for your horse(s), and therefore whether it should or should not be used again in the future.