Don't Guess. Test.



Isn’t rotating enough?

“Think about it this way: You would never randomly use an antibiotic to treat a suspected infection. It wastes money, it wastes therapeutic time just when speed is of the essence and it increases the risk for developing resistant pathogens. That same school of thought must now be applied to equine dewormers.”

– Frank Hurtig, DVM, MBA, director, Merial Large Animal Veterinary Services,
Forget What You’ve Been Taught. It’s Time to Rethink Rotation.

What is Parasite Resistance?

Resistance develops when the recommended dose of dewormer does not kill 100% of the parasites inhabiting an animal. This process of selection allows resistant survivors (those not killed by the dewormer) to mate with other resistant worms and subsequently pass resistant genes onto their offspring. Resistance becomes a clinical problem when there are a high number of resistant worms within the treated population leading to treatment failure and clinical disease. The rate at which modification to the parasite gene pool occurs within a given population varies depending upon a number of factors including: the frequency of exposure to a particular class of anthelmintic, the immune status of the individual horse and the size of the parasite population in refugia (the population that has never be exposed to anthelmintics).

What is a Fecal Egg Count Resistance Test (FECRT)?

Administering a dewormer does not guarantee that animal has been dewormed, therefore it is important to periodically check and see if the drug you are using is working in your horse. You do this by conducting a test before and after applying a dewormer. The time from the deworming to conducting the second test varies with each drug type but a safe timeframe is 7-10 days. More about the FECRT.

Don’t you need a centrifuge to conduct a proper fecal test?

We recognize that there is confusion around the sensitivity of the modified McMaster method and the need for centrifugation. In companion animals like dogs and cats a centrifuge is necessary in the testing process because the presence of one parasite egg is enough to warrant treatment.

However, grazing animals such as horses are different. It is recommended that only horses with egg counts over 250 eggs per gram be dewormed. Centrifugal flotation techniques will identify EPGs as low as one, whereas the McMaster method will identify EPGs as low as 25. This is a trivial difference when you look at the big picture.  Would you treat a horse with an egg count of 1 any differently than a horse with an egg count of 25? The leaders in equine parasitology agree that the modified McMaster method is more than sufficient since treatment is not necessary when egg counts are less than 250.

“Ironically, resistance is the direct result of the ready availability and ease of administration of dewormers.” 

– Harold C. McKenzie III, DVM, MS, Dipl. ACVIM. –  Veterinary Practice News


What about a daily dewormer?

“There’s some epidemiological evidence to suggest that widespread use of daily dewormers might be hastening the process of resistance. This means that if you think a daily dewormer is the ideal choice for a high-risk horse, it may be exactly the opposite.” Learn More.

What are we really testing for?

Most of the parasite eggs seen on a fecal exam come from one of many small strongyle species–collectively known as cyathostomins. Cyathostomins are ubiquitous parasites of grazing horses, and are currently considered one the most significant pathogenic internal parasites in horses. Drug-resistance among small strongyles has been intensely documented throughout the last decade.In addition to small strongyles, Parascaris equorum commonly known as roundworm, or ascarids also constitutes a major threat to equine health. Unlike small strongyles, ascarids are found most commonly in foals and younger horses. Adult horses usually have low numbers due to the development of immunity during the course of infection. However, it is important to note that the reduced efficacy of anthelmintics and development of multiple drug-resistance to equine ascarids has been reported in many countries including the United States.

How often should I test?

Parasites know when weather conditions are ideal to exit the body and have the best chance for survival. Spring and fall are peak seasons. But this really depends on your region.If you don’t see eggs in the sample it may mean that the adult worms are not shedding eggs at that time and within a week or two testing again will show an infestation. Therefore, regular testing is suggested. See our Equine Deworming Guide.

What is Strategic Deworming?

“Parasite problems add up to a numbers game. Some horses develop natural resistance. Egg counts in mature horses show that many of them don’t have levels that would cause problems, yet another horse in the same pasture, same conditions, same age, may have a tremendous number of worms.”  ~Thomas Craig, DVM, PhD, of the Department of Veterinary Pathobiology at Texas A&M University.

“Resistance to dewormers by cyathostomes is an unfortunate, but logical outcome given the overuse of anthelmintics.” 

– David Pugh, DVM, MS, DACT, DACVN

What about the parasite eggs that cannot be found in an Eggzamin modified McMaster test?

There are more than 150 species of internal parasites that can infect horses.  Fecal egg counts are intended to accurately quantify the most common and pathogenic intestinal parasites i.e. strongyles and ascarid, and to prevent further development of anthelmintic resistance within theses species. There are some parasites that are not good candidates for FECs including tapeworms which produce eggs intermittently or lungworms which rarely have recoverable eggs in horses. Therefore, it is important to remember that a low EPG counts does not mean a complete lack of parasites in your horse. For that reason, annual or semi-annual deworming programs should be maintained even if your EPG numbers are low. Unlike the parasites identified in FECs, most, if not all of the parasites that cannot be recovered in a floatation are readily susceptible to current anthelmintics.

Deworming strategies are multifactorial and lack a “one size fits all” approach.  Despite the few limitations of fecal egg counts, they are still considered the gold standard for obtaining excellent information about the parasites of concern, and can help a great deal with the design of effective, responsible deworming programs that will help to minimize resistance.

Look at a few of the non-floating parasites.

Learn how to manage parasites in your geographical location.

What about encysted strongyles?

If an effective control program is in place, encysted cyathostomes should never be a major target of control efforts.  Encysted cyathostomes only become an issue when large numbers build up after failed control efforts or some rare environmental conditions where large numbers of larvae are present.

Dr. Craig Reinemeyer, President, East Tennessee Clinical Research, Inc. says “I’m frequently asked when one should incorporate a treatment for encysted larvae in the course of an annual program.  My answer is “never”; you shouldn’t need to.”

Larval cyathostomiasis is a management problem.  If it’s a herd issue, it’s associated with mild, wet environmental conditions, over-stocking, failed control measures, and managerial deficits.  If an individual horse develops it, chances are that animal has a unique susceptibility that is genetically determined. In other worlds, that animal shouldn’t get anywhere near a breeding shed.

Understanding the life-cycle of small strongyles is the first step to intervention. By combining good pasture management with a strategic deworming program, small strongyles can be controlled effectively. Remember that “control” is the key word, rather than elimination.

What about diatomaceous earth for parasite control?

The use of diatomaceous earth as a dewormer for internal parasites in horses is very questionable. Diatomaceous earth fed to the horse probably would be overwhelmed by and incorporated into the remainder of the horse’s feed so that very little of it actually would come in contact with internal parasites.

What about foals?

Research suggests that foals should not be treated routinely for any worms until they are at least 60 days old. Foals may have some parasites at a younger age, but they are ones we probably can’t do much about because the efficacy of these dewormers gets better as the worms get older. The younger the worm is when you expose it to the drug, the less likely the drug will work.

Dr. Craig Reinemeyer recommends owners and managers discontinue deworming at foaling time. “With resistance issues we now face we should stop treating horses so frequently and only focus on treatments that are absolutely necessary,” he states. “We used to treat mares in late gestation to prevent transmission of Strongyloides (threadworms) to their foals through the milk. This is not a serious parasite and is easy enough to treat if it does cause clinical problems such as diarrhea. It will not kill a horse without warning. Current recommendations are moving away from those old deworming programs and schedules we used to follow meticulously.”

What about Eggzamin for dogs and cats?

Unlike horses, dogs and cats harbor a number of parasites that can infect humans resulting in life-threatening illness. These types of parasites are referred to as “zoonotic” meaning they possess the ability to infect people as well as animals.

Due to the public health implications, there is no acceptable level of parasitism in companion animals, therefore monitoring parasite burdens via the modified McMaster technique is not an appropriate method of management. A qualitative fecal flotation should be performed by a veterinarian to determine the presence or absence of parasites and appropriate treatment administered immediately.

Although drug-resistant parasites are a common finding in horses and livestock, this phenomenon has not been reported in companion animals. The Companion Animal Parasite Council advocates year-round, broad-spectrum parasite control with efficacy against heartworm, intestinal parasites, fleas and ticks.

What if I don't know how to use a microscope?

The Eggzamin equipment has been designed for ease-of-use. Your kit comes with everything you need for unlimited FEC’s, our clear How-To Instructions, a Microscope Users Manual to familiarize you with the components of your equipment, and our website and images are available to help you learn to identify parasites.

The majority of surveyed farms have drug-resistant parasites. Does yours?