Worm count results
If the result shows <50 EPG, this means that no eggs of the relevant worm species were detected. Fifty eggs are the threshold value of the McMaster test as performed at the parasitological laboratory. Theoretically, it is possible that a horse has an EPG = 50 for a worm species (10 eggs per gram of feces) and that the result still shows <50. Very low egg counts are therefore not detected. Very low EPG values have no consequences for health and no infection is present. With the McMaster fecal test, the EPG increases in steps of 50.
The following values can be shown on the result: <50, 50, 100, 150, 200, 250, 300, 350, 400, etc. The advice whether or not to treat a horse depends on the result of the fecal test (= the EPG), the age, and the conditions in which the horse is kept. If an infection is found, we will always ask you to answer a few questions so that we can provide a tailored deworming recommendation. Whether a horse has a light or heavy worm infection is not determined solely by the EPG, but also depends on the age and housing of the horse.
As a general guideline you can assume:
Explanation of your result
This is a question we are often asked. Finding worms afterwards causes a lot of concern and sometimes even leads people to stop doing fecal tests altogether. However, a fecal test is not performed to determine whether or not a horse has worms. Every horse has worms — even one that has just been dewormed. The available dewormers only kill part of the worm population present in a horse.
Please note that eggs are only shed by adult worms. If no eggs are found in the fecal test but there are still developing juvenile larvae, these larvae may become adults within two weeks and then start laying eggs. That is why it is very important to carry out fecal tests frequently.
Finding worms in the manure is nothing to worry about if the horse is fit and healthy. A horse can build up strong natural resistance against gastrointestinal worms and eliminate them naturally. If the population grows and the horse can no longer manage it on its own, then treatment is required. If you find a worm in the manure, take a picture and send it to us by WhatsApp so we can check it for you.
With roundworms, we sometimes even see an adult worm being found on the very day the fecal sample was taken, while the fecal test shows no roundworms present. This can happen when only adult male worms are present, and like other animals, males cannot lay eggs.
We do indeed receive many questions about bot flies in horses. Because of all the pictures on the internet of bot fly larvae attached to the stomach wall, many owners become worried. However, bot fly larvae are not highly pathogenic. Since infection levels are usually low, few horses experience problems with bot larvae. If an owner wishes to treat against bot flies — for example, because many yellow eggs were seen on the horse’s coat — we advise doing so after the first serious night frost. During frost, the free-living bot flies die, and the risk of reinfection after treatment is eliminated.
We always recommend sending in a fecal sample in the autumn. This provides a clear picture of the infection levels on the pasture, and we can then provide advice to prevent further problems with bloodworms during the winter.
Based on the case file, age, environment, symptoms, questionnaire, and seasonal risk, it is assessed what is still advisable to conclude the case for the year, and treatment may be prescribed for worms that are difficult or impossible to detect through worm testing.
We count all worm eggs and will report the total. First, we count the eggs of adult large and small strongyles. The result does not distinguish between large and small strongyles. We also check the feces for the presence of roundworm and threadworm eggs. You can additionally order tests for lungworm and liver fluke.
We also test for tapeworm and pinworm, but these are not reliably detectable through fecal testing. To rule out these intestinal worms, additional testing is recommended.
If tapeworm eggs are found, they will also be listed on the report. If the fecal test is positive for tapeworm, we can confirm that your horse has tapeworms. However, if no eggs are found, we cannot rule out the presence of tapeworms.
If you want to test for tapeworm, the best option is to carry out an EquiSal Tapeworm test. Tapeworms produce their eggs in packets or segments. Sometimes, you may even see segments in fresh manure.
If worms are detected, we will always provide you with a personalized treatment recommendation. This way, your horse’s health comes first, and unnecessary deworming can be avoided.
Feces are also checked for sand. To get an accurate picture of the amount of sand, however, it is important to test for several consecutive days.
You can easily do this yourself. For instructions, go to this blog.
Horse bot larvae cannot be detected through fecal testing. The yellow eggs of the horse bot fly are, however, easy to recognize on the horse’s coat. These are mainly visible in summer and autumn. In late spring, bot larvae can sometimes be seen in the manure.
Pinworms are almost never visible in manure. They lay their eggs around the horse’s anus. Therefore, the eggs are usually not present in the feces. To prevent the spread of pinworms in a herd, we recommend deworming in case of a pinworm infection.
Tapeworm eggs are also rarely found in manure. The value of a negative result is limited, as it is still quite possible that tapeworms are present. That is why the laboratory recommends testing your horse twice a year with the EquiSal Tapeworm test.
There are several situations in which a worm egg count provides essential information about worm infestations in your horse. Below we have outlined some examples for you.
Infective larvae can survive on pasture for up to 3 months, especially at lower temperatures. Moderate to severe frost kills the infective larvae. Research has shown that due to mild winters, pastures can remain contaminated until January. This means that horses can indeed become infected well into the winter. Therefore, a worm control program also includes the winter months.
You can send pooled samples yourself, but you must mix the manure properly beforehand. Take an equal amount of manure from each horse, place all manure in a bucket, and mix thoroughly. Then take a small handful of this mixture and send it to the laboratory.
However, the laboratory does not recommend pooled manure samples. In practice, group samples often test positive, which then leads to all horses being treated. This is not the intention.
Animals that are kept exclusively in a clean stable or on a sand paddock have little to no contact with infectious larvae present on pasture and therefore have a lower risk of reinfection. However, the small strongyle also has an internal process. The larvae can emerge from the intestinal wall and develop into adult worms that lay eggs. A horse kept only on a paddock or in a clean stable does have a reduced risk of worm infection, but not a complete absence of risk.
t is often said that moxidectin is more effective against bloodworms. However, this only applies to the larval stages of bloodworms. Ivermectin has little to no effect against bloodworm larvae.
Larval stages are only relevant in young horses or in horses sensitive to infections that grazed on heavily contaminated pastures during the previous late summer and autumn. In such cases, the ingested larvae overwinter in a kind of dormant stage in the intestinal wall. For these horses, moxidectin is useful, because treatment (in November/December) will also kill these larvae and reduce the risk of a bloodworm infection.
Due to resistance, we only have two active substances left against bloodworms, and we must use them sparingly.
For treatment during the grazing season, ivermectin is therefore preferred. Moxidectin should be reserved for high infection levels or for winter treatment. With ivermectin, we can achieve the main goal: preventing pastures from becoming heavily contaminated and reducing infection pressure.
We are seeing more and more short courses being offered to learn how to perform fecal tests yourself. Unfortunately, in practice this often goes wrong, with all the risks that come with it. Of course, it is good that horse owners want to learn more about gastrointestinal worms, but due to the complexity of the examination and the interpretation of the results in relation to management practices, expertise is essential.
👉 Take your horse’s health seriously and have fecal tests carried out by professionals
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