Ask The Vet: Internal Parasites

Question: How accurate are “mail order” test kits? How long is the fecal sample viable? If I receive a questionable result, what should I do next – re-test, or go ahead and deworm? 

Answered by, Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky, Courtesy of AAEP

Answer: We tested this in a study, and we found that if samples are kept airtight and mailed in fresh, the parasite egg counts are fine if samples are done within a week upon collection. If they are shipped with icepacks to stabilize storage temperatures, it gets even better. So, there is no reason to believe that mail order test kits should be bad or less reliable than direct analysis if everything is done properly. I am not sure what you mean by a questionable result, but retesting is never a bad idea if you have reasons to doubt the result. Just keep in mind that two counts generated from the same sample are never going to be exactly alike. If you suspect parasitic disease, you shouldn’t waste time on running fecal egg counts, but just go ahead and deworm that horse.


Question: How effective is feeding diatomaceous earth at regular intervals? 

Answer: Unfortunately, diatomaceous earth has not been found to possess any antiparasitic effects when evaluated in research studies.


Question: What kills adult threadworms, also known as neckworms? 

Answer: The neck threadworm, also known as Onchocerca is a filarial parasite infecting horses. The adult worms reside in the neck (hence the common name) and the (offspring) microfilaria live underneath the skin waiting for a biting midge (Culicoides) to pick them up. There are no known effective treatments for the adult worms, whereas ivermectin has been found effective against the microfilaria.


Question: Is there still a point in using drugs like Fenbendazole or Pyrantel Embonate, or is it better to stick with Moxidectin and Ivermectin?

Answer: Yes, there is still a point with these anthelmintics, but they will have to be used differently now. Both of these drugs have lost efficacy against small strongyles in recent years and resistance appears to be widespread. There may still be individual farms here and there where one of these might still work, but chances are small these days. However, they still have good efficacy against other parasites such as ascarids and pinworms. In addition, pyrantel is also effective against tapeworms when given in a double dose. So every dewormer still has a place in equine parasite control and should not be completely abandoned.


Question: I do fecal checks on my horses. How reliable are they?

Answer: Fecal egg counts are essential for checking dewormer efficacy. If current guidelines are followed, the fecal egg count reduction test is both reliable and useful. Egg counts are also useful for determining whether an adult horse is a consistent low, moderate or high strongyle egg shedder. This pattern exists in all horse populations. Finally, egg counts are also very reliable for detecting ascarid (large roundworm) infection in foals, weanlings and yearlings. This is important as it affects the choice of dewormer. So egg counts are useful, important and necessary. However, it is important to be aware of egg count variability, which can be substantial. Your veterinarian will know how to interpret a given count.