Do faecal egg counts tell you how many worms your horse has?

Do faecal egg counts tell you how many worms your horse has?

We love our informed, empowered, and connected WormGuiders who know just how valuable reliable faecal egg counts (FECs) can be in looking after their horses.

Not only are WormGuiders helping to spread the word about the recommended modern changes we must make to safeguard our ability to control horse worms now and into the future - they also ask the BEST questions too!

Many of our devotees want to know the reasons why faecal egg counts (FECs) do not tell you if your horse has worms, how many worms or worm-related disease. So, without further ado and with the help of Dr Martin Nielsen here`s why:

  • Worms have a lifecycle. They go through stages of life. When worms are immature, they don`t lay eggs yet. When they grow to become young adults, they lay more eggs. When they are close to the end of their life, they lay less eggs or not at all. So, it`s impossible to correlate the number of eggs to the number of worms.

Interested in the lifecycles of worms? A basic understanding really does help with your up-to-date worm control strategy. Travel over to our video library where Dr Martin Nielsen explains the road maps worms take to reach their ultimate goal- you guessed it, to make more worms. It`s amazing.

  • At least 28 species of small strongyle worms have been reported across different climatic regions in Australia ( Saeed et al.,2015) all with eggs similar in appearance. They are described as strongyle-type worm eggs in your horse`s egg count result. Some species lay more eggs than others, so it`s impossible to correlate the number eggs to the number of worms.
  • If a horse has a large load of female egg laying worms, each female worm lays fewer eggs. If a horse has a small load of female egg laying worms each worm lays more eggs. So, it`s impossible to relate the number of eggs to the number of worms.
  • Adult horses develop a certain level of natural immunity to small strongyle worms- a parasitic worm all horses have. But not all horses shed worm eggs in their manure to the same extent. Horses with a strong immunity (low egg shedder) do not permit the worms to lay as many eggs as horses with a weaker immunity (high egg shedder). So, it`s impossible to relate the number of eggs to the number of worms.

Cue picture…

** told you!

Two Horses. Let`s say they have the same number and types of worms and lifecycle stages, yet these two horses have vastly different egg counts. One horse has an immune system that can suppress egg shedding (releasing eggs in manure on pasture) and the other doesn’t.

Correcting the misconception

A high faecal egg count (FEC) doesn`t necessarily mean a high worm burden.

You`re probably thinking why the FEC do we use FECs, what`s the point?

As our expert WormGuider vet Dr Charlie says in the video on our home page, “Counting those worm eggs reliably gives you the information you need to make smarter deworming decisions.”

Our new goal is to preserve effective chemical anthelmintics (dewormers) by stopping the unnecessary overuse of our precious worming medications.

We need to keep effective dewormers for horses that actually need treatment. You`ve probably heard the news by now that the rise of resistant worms that no longer respond to deworming medications is an alarming trend to equine parasitologists and veterinarians, and with no new drug classes available in the foreseeable future (if ever!) -  we are potentially facing a catastrophic health crisis.

Here are the resistance profiles in Australia and around the world

Warning alert: you may be shocked!

Horse scientists and parasitology research provide a solution to manage our way around devastating dewormer resistance. We can`t stop it but we can slow it down… or speed it up.

Slowing it down sounds like the best option, don`t you think?

… and hope the pharmaceutical industry will find a new anthelmintic (dewormer) drug for the equine market.

Warning alert: they will likely be far more expensive if at some point in the future a safe deworming drug is developed.

The current solutions

Reliable worm egg counting gives us the information we need to make smart deworming decisions.

Our main goals are:

  1. Performing faecal egg count reduction tests (FECRT) to monitor anthelmintic (dewormer) resistance among small strongyles (cyathostomins). The FECRT remains the gold standard for detection of anthelmintic resistance, which is always diagnosed in the worm population that is shared among the herd. We need a minimum of 6 horses.

There is so much resistance out there - Dr Nielsen emphasises that deworming without once a year resistance testing is irresponsible.

Don`t have a herd of horses?

2. The Truth Teller FEC test tells us whether our chosen worming treatment actually works. It`s simple, first we test with the Super Surveillance FEC before deworming and then we check 10-14 days later with the Truth Teller FEC to compare the number of eggs - worming failure or success? Do this once a year to avoid misguided effort and waste of money on something doesn`t work.

WormGuide`s testing technique is highly suitable for resistance on a property level and checking a chosen wormer works because it detects even low numbers of eggs to avoid false reporting.

3. Identifying horses that need additional deworming beyond the recommended twice-yearly basic foundation treatment with the right worming product for all horses in spring and autumn. Every 6 months at the appropriate times of the year when environmental conditions favour larval development on pasture.

This is part of the recommended targeted (or selective) dewormer treatment protocol that helps slow the development rate of harmful resistance.

The Super Surveillance performed twice a year on all adult horses allows you to classify horses based on their egg shedding level because not all horses shed worm eggs to the same extent. The 80/20 rule means twenty percent of the horses on a property shed 80% of the eggs on pasture.

The main aim of the FEC is to identify the low and the high egg shedders. The high shedders spread most the eggs on pasture and require an additional treatment beyond the basic foundation treatment. No more guesswork or rote deworming all horses!

So, a modern 21st century high performing egg counting technique can yield valuable and useful information for:

  • Identifying dewormer resistance on the property level (increasingly important)
  • Checking the dewormer works (increasingly important)
  • Identifying high egg shedders so we know which horses are primarily responsible for the infection pressure 
  • Tailor the worm control strategy
  • Identifying the presence of ascarid (roundworm) eggs in young horses

But. . . FECs cannot tell us heavy worm burdens or diagnose disease.

How do you feel? Hopefully more informed, empowered and connected. At WormGuide science and research are at the heart of everything we do, and we are here to help you take control.

Grab our hero, the fecing good collect and send Kit today and start FECing to treat your horses right .


Want to watch a 12-minute video? Dr Nielsen veterinarian and one of the foremost experts in the field of equine parasitology at the University of Kentucky's Gluck Equine Research Center talks about the importance of faecal egg counts, what are they telling us and how we are supposed to use them.

And he even gives you free `secret` info. Who doesn`t love a secret!


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