Quantitative parasite analysis for manure on the outside of your boots

Farm Forum

Parasite resistance to the drugs we most commonly use is becoming an increasing concern in our horse populations. For many years veterinarians and horse owners have been using rotational de-worming to combat parasites. This aggressive de-worming protocol may now be contributing to the development of resistant parasites. This could eventually lead to a devastating parasite problem in the not so distant future and we could be faced with a parasite population that does not respond to any of the drugs currently available. If this occurs, we would essentially be back at square one with parasite control. Prior to effective parasite control, horses were plagued with unthriftiness, plus a marked increase of colic incidence and premature death.

In an effort to reduce the development of resistance to de-worming drugs, equine practitioners have adopted a new strategy for combating parasites in our horse populations. It is imperative that you, the clients, help us maintain the effectiveness of the currently available de-worming drugs by participating. Using published, evidence-based research we have changed our de-worming recommendations.

Our goal with de-worming from now on will be to de-worm only as needed, based upon the results of quantitative fecal exams. These tests provide much more information than a routine fecal used for basic screening. The quantitative fecal exam actually provides the number of parasite eggs per gram of feces that exist in an individual horse so we can categorize them into low, moderate or severe worm burdens. We will use these numbers to determine the ideal de-worming strategy for individual horses and barns.

Just like certain people are more susceptible to colds and flu, certain horses carry a much higher parasite burden than others. In fact, research has shown that 20% of the horse population harbors 80% of the parasite burden. Clearly, as these horses are the ones contaminating the environment, they are the ones that need to be de-wormed most regularly. This does not mean that we stop treating other horses. It is important to continue a modified de-worming program for all horses, with the horses with the highest worm burdens being medicated most frequently.

De-wormer dosage is also important in developing resistance. Weight tapes are usually readily available at most vet clinics and feed stores. Always make sure your horse has as an empty mouth to aid in prevention of expelling the de-wormer with their food back on the ground. For the exception of some young or ill horses it is usually best to risk overdosing if you think they wasted some on the ground by repeating rather than under dosing. It is best to consult your veterinarian for specific de-wormer brands and circumstances.

What does this mean for you now? When your veterinarian visits your farm this spring have one fecal ball from each horse in a labeled zip lock bag. A fresh sample is ideal, or at least kept at a refrigerated temperature. Once the results come in, your veterinarian can help design a program for your horse(s) and the environment they live in. While this program certainly involves more effort, we feel that it is exceedingly important to do our part in keeping de-wormers effective.

Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or