Important Information

What you need to know about managing parasites in your yard
  • Scientific evidence has shown that only about 20% of horses have high worm egg counts (less in yards where horses are stabled for most of the day, e.g. racing yards) and actually need to be de-wormed

  • Where there are high egg counts, these are often resistant to treatment, and in some cases deworming treatments have been shown to increase rather than decrease worm egg counts – routine de-worming is therefore NOT the answer. 

  • Owing to increased resistance to treatment, there is no longer a “silver bullet” treatment to eradicate all worms in all horses every time and often veterinary input is required to address the problem.

  • Worm egg counts should be done regularly, as each count can reveal different status, the extent of paddock contamination, and treatment requirements owing to the life cycle and species of parasite

  • If your horses are exposed to standing water, streams or dams, they should be tested for Gastrodiscus in addition to a standard worm egg count.

  • Pinworm eggs cannot be found in faeces, and can be simply diagnosed and treated appropriately when a horse scratches only its tail, but not its mane or other parts of its body.

  • If a horse has a borderline egg count, it could fluctuate up or down, and therefore should be retested within 30 days (at no further charge to you the owner) to see if treatment is required.

  • Following Worm-Ex Lab prescribed treatment a horse should be retested within 10 to 30 days to check the efficacy of the treatment (this too is at no extra charge)

  • All interpretations and advice will be based on a sound veterinary understanding of equine parasites and the environment.

Life Cycle.jpg
Signs of a possible worm problem

• Weight loss

• Colic

• Dermatitis (Pinworms Strongyloides  westeri

       Onchocerca cervicalis Habronema - summer sores)

• Central Nervous System Signs (Helicephalobus deletrix)

• Respiratory signs (ascarids and lungworms)



In adult Sport-horses in Gauteng, we are seeing less than 4% of horses needing deworming. This means horses with 350 or more worm eggs noticed per gram of dung tested by McMaster slide examination.

So about 96% of horses appear to not need deworming.

The more one tests one horses over the years the more accurate and precise the data becomes on how your horses are coping with your specific management procedures.  Overall total egg counts for an entire yard can be calculated and risk assessment for pasture and paddock can be calculated. 

Testing is guaranteed to change your deworming decision making.  This is the exact reason why new diagnostic technology is being employed as we should not be doing what we did 40 years ago.  We should be doing things better for client, horse and environment.

However, there is a slight amount of merit in doing this seemingly senseless act once every two or three years! To make this point clearer I wish to take you back to the findings of the research groups in Denmark and in Kentucky, the home of the flat racehorse breeding industry and where most of the first-class equine parasite research is coming from.

So, as you may be aware, Denmark has started to make deworming of horses illegal unless a competent lab has found worms to be present in sufficient numbers. This is called the Selective or Targeted approach and was adopted into law in Denmark 20 years ago. Since then a few forward-thinking individuals, like you reading this article, and in countries like Holland, Sweden and Finland have followed suit. Hooray, these people are thinking about the consequences of excessive, uncalled for, deworming.

Kentucky by contrast deworm by calendar month. This is called Strategic or Seasonal deworming. However, this is largely a system based on the needs of foals and young horses and this should not apply to adult horses.

There is a new type of molecular test called PCR testing where one can look for a genetic fingerprint of a specific pathogen, bacteria, virus or, in this case, worms. This specific PCR test has been set up to look for the Strongylus vulgaris (large strongyle) parasite egg in particular. What has been uncovered is that this “bad boy” parasite, whose lifecycle includes time inside the arteries of horses, is not present in Kentucky, but is present in small numbers (14.1%) in Denmark. So, while Kentucky may have a dangerous deworming policy, they can show some definite positive effects of this system, whereas Denmark may have the gold standard ideal in mind but there is a draw back. The bad boy parasite S vulgaris is raising its ugly head here!

So, WORM-EX LAB has come up with a largely unique solution.

We have married the two systems into one unit to get the best of both worlds. We don’t want to over deworm and neither do we want the bad boy parasite to get a toe hold in our clients’ horses. Also, current testing methods for stomach bots and tapeworm diagnosis are either non-existent or mildly flawed as they under-represent the actual incidence in horses, and perhaps gives a false sense of security. We need therefore to counter this by taking precautions against possible infection.

So, we are saying that clients who feel uncomfortable not deworming at least once in a while may want to consider meeting on neutral ground. We are suggesting that, once every two years, all the horses in your yard get dewormed with an ivermectin dewormer plus praziquantel. This will cover tapeworms, stomach bots (Gasterophilus) and Strongulus vulgaris but will not destroy the small strongyle refugia (dormant worms in the gut lining), so immunity development to these more common parasites will continue, unabated.

And what is the best time to do this? Autumn is supposedly the best time to get rid of tapeworms which generally have a single cycle per year with the highest prevalence at the tail end of summer. However, winter is the best time to clear horses of bots when the free flying bot fly is at its least prevalent. So, doing one broad spectrum dewormer in winter will cover all these bases adequately.

As most Gauteng horses have been experiencing regular unnecessary deworming we feel that one should deworm only based on WEC results for now. Then, come Winter 2020, that one embarks on an “entire yard” deworming spree with ivermectin plus praziquantel that will last till 2022 for large strongyle, tapeworm and bots.

Regular WEC testing between these dates remains important to pick up the individuals with counts of 350 and above.


"Deworming horses may be something you've been doing the same way for as long as you can remember - most likely every eight weeks or so, rotating between classes of dewormers with each treatment. However, you should know that this old-school approach is not only quickly becoming outdated; it's also a waste of time and money, and builds parasite resistance.

* Commonly used strategies for parasite control in adult horses are based largely on knowledge and concepts that are more than 50 years old. A re-examination of these practices is now necessary based on the important changes that have occurred in the parasitic fauna of equines.
* Horses should be treated as individuals and not according to some routine.
* Working with your horse doctor to create a targeted deworming plan for each horse/farm based on pre- and post-deworming faecal testing is actually less work, less expensive and more effective than the rotational deworming program of the old days.
* Don't rely on dewormers alone, proper pasture maintenance is also critical when it comes to parasite control (like regularly removing manure from pastures rather than dragging the fields).

TAKE HOME MESSAGE : rather than just going through the motions this fall, be smart and consult your veterinarian on how to best deworm your horses!

Related resources : The full AAEP Parasite Control Guidelines can be found at…/InternalParasiteGuidelinesFinal5.23.19.p…"