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Clinic Hours:
Mon-Fri 8 to 5:30
Sat. by appointment only

31310 Woodhaven Trail
Cannon Falls, MN 55009

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Phone Numbers:
651-258-4050 office
651-258-4051 fax
651-222-0885 Twin Cities


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Parasite Control and Prevention

The number of parasites, which impact our horses, are increasing and building a resistance to the most common paste wormers. It is proven, that tube de-worming remains the most comprehensive and effective way to eliminate parasites with confidence. Parasitic infestation may cause permanent damage to the intestinal tract of your horse, even while it appears to be healthy. Parasites can be minimized greatly if a strategic de-worming program is used.

Paste wormers are somewhat effective when utilized as part of a more comprehensive plan. Unfortunately unless properly administered, much of the paste wormer is spit out and not digested by the horse. Dr. Winter believes that including regular
tube de-worming in your de-worming program is the best technique to ensure your horse’s quality of health. Because tube de-worming delivers the treatment directly to the gut where parasites reside, it has optimal results. CVS created our own tube de-worming study. We wanted to compare the efficacy of paste wormers and tube de-worming. We took seven horses who share a pasture together. Five of the horses were on an every other month, rotational, paste de-worming program. Then we placed the remaining two horses on a rotational, tube de-worming program. After a few months, we performed a microscopic fecal examination on the horses. Through our examination, we discovered the horses that had been paste wormed, had a significant amount of parasite eggs present in their feces. Whereas the horses that we tube de-wormed, no parasite eggs were detected in their feces.

Dr. Winter has tube de-wormed
many thousands of horses for over forty years and has never ran into any complications associated with this method of de-worming. Strategic de-worming and parasite control is his passion. Therefore he believes that rotating the class of drug/chemical in the de-wormer is an important part of the parasite control plan.

Since parasites are primarily transferred through manure, good management is also the key.

The American Association of Equine Veterinarians Recommends:

Pick up and dispose the manure droppings on a regular basis (twice weekly)
Mow pastures regularly and break up manure piles to expose parasite eggs and larvae to the elements
Rotate pastures by allowing other livestock, such as sheep or cattle, to graze them. Thereby interrupting the life cycles of equine specific parasites
Group horses by age to reduce exposure to certain parasites and maximize a de-worming program
Minimize horses per acre to prevent overgrazing and reduce the fecal contamination per acre
Use a feeder for hay and grain rather than feeding on the ground
Remove bot eggs quickly and regularly from the horse’s hair coat to prevent ingestion
Rotate de-worming agents, not just brand names, to prevent chemical resistance

There are many different types of equine parasites, each causing its own unique damage to the horse. For example, the stomach worm larvae can expand a wound and prevent it from healing, causing “summer sores”. Small strongyles burrow into the intestinal wall and can cause weight loss, diarrhea, and colic. Pinworms cause the horse to become extremely itchy in the anal area causing the horse to rub its tail hair off. Roundworms burrow and hatch in the intestines, and the bloodstream carries them throughout the internal organs. These are just a few of the many parasites that are out there infecting our horses everyday.

Current research confirms that parasite resistance to anthelmintics is a growing problem worldwide. Rotational de-worming programs (every 6 to 8 weeks) are no longer effective because they contribute to the parasite resistance. The most logical way to prevent this from happening is to minimize the frequency of paste de-worming or daily de-wormers. By reducing the selection pressure placed upon the parasites the resistance problem will be reduced. Proper rotation of the different drug classes is important because some parasites survive the treatment with certain anthelmintics and then reproduce a new generation of drug resistant parasites known as the “super worms”. De-worming is no longer a simple do it yourself procedure, but a complex multifaceted issue with serious health consequences for your equine companions.

To fight the resistance CVS suggests:
CVS stresses the importance of having fecal egg counts done 2 - 4 times per year.
Fecal egg counts (FEC) measure the concentration of EPG (eggs per gram) of your horses manure. Dr. Winter is then able to interpret and diagnose the drug resistance issues in order to determine which de-wormers should be used as well as the frequency of treatment for each individual horse. (FEC) should be done 10 to 14 days after de-worming to establish the effectiveness of the product used. A second fecal should be done at the egg reappearance period (ERP).The (ERP) is a predictable interval where the fecal egg count remains low after an effective de-worming agent is administered. The time frame varies according to the product used.


Egg Reappearance Period (ERP)


2-4 weeks


8 weeks


4-6 weeks

Ivermectin & Praziquantel

12 weeks


12 weeks

The second fecal helps to determine, which horse has a high parasite load and/or if your paddock or pasture has a parasite problem with re-infestation. By identifying this problem, CVS can provide you with a targeted treatment for each individual horse and/or environment. Dr. Winter will evaluate your situation, estimate your horse’s weight, and customize an individualized de-worming program that best suits the needs of your horse(s) and your facility. For optimal impact, he will advise you to administer an effective dose of the right anthelmintics at the appropriate time of year.

CVS encourages you to protect the environment of your horse to prevent them from getting infected with the parasites in the first place.

Remove feces from the stalls daily and paddocks twice weekly. By doing so, the infective stage of eggs and larvae is decreased and the life cycle is interrupted.
Remove bot eggs from the hair coat twice weekly (A flea comb works well)
Rotate the paddocks or pastures and don’t over graze or overcrowd them
Rotate livestock species in pastures when possible
Compost the manure properly if you intend to spread it on your pasture.
Feed horses away from contaminated areas using feeders for hay & grain
Harrow cautiously (hot summer days) & leave pastures vacant for 2 weeks
Quarantine and de-worm all new horses before turning them out with your herd. Use a larvicidal dose of fenbendazole, followed by Ivermectin or Moxidectin. In 10 to 14 days post treatment have a fecal egg count done to test the wormers efficacy.


35 % of horses account for 85% of pasture contamination.

Early in the season, the horses with severe (>500 EPG) fecal egg count) should be separated. Have them tube de-wormed or worm them with a larvicidal dose of fenbendazole. These horses are the individuals primarily responsible for contaminating your pastures. Also de-worm the horses with moderate egg counts (200 to 500 EPG)


Click here to print/view the Paste De-wormer Chart.

Click here for Equine Intestinal Parasites.


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