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Should You Rotate Your Horse Dewormer?

a horse owner discusses rotating horse dewormer with a vetTo rotate or not to rotate? That is the question when considering how best to rid your horse of parasites via deworming. When it comes to horse ownership, creating an effective parasite control program is critical. Just as you don't take your horse's nutrition or vaccination program lightly, you should place special emphasis on your deworming methods.

Internal parasites can be silent killers in our horses. These worms and parasites can infect our horses and cause extensive internal damage without our knowledge. The effects of parasites can range from dull hair coat to colic to diarrhea and even death.

There are over 150 species of parasites that can infect horses. However, in the United States we are most concerned with controlling four of these parasites. The not so fab four are:

  • Large Strongyles
  • Small Strongyles
  • Roundworms
  • Tapeworms

The most common way to control parasites is through a chemical deworming program. We first started interval deworming back in the 1960s to control large strongyles. Fast forward 50 years later and a plethora of research has been conducted on products to control parasites. Now that we know which products most effectively control parasites the new question is, "Do we need to rotate these products or always administer the same product?" This debate has arisen as we try to control drug resistance in horses.

Rotating Dewormers

Many horse owners rely on a rotational deworming program to effectively control parasites. As the seasons change, so does the class of dewormers they treat their horses with. The theory behind rotational deworming is that by switching up the class of dewormers, not only do we combine the benefits of all classes, but we manage resistance to a particular class of dewormer. Tony Brubaker from Pfizer says, "It's important to rotate between the three major dewormer classes and use them at appropriate intervals based what you last used, what time of year it is and how susceptible your horse is to parasites."

Those who support rotating horse dewormers know there are detractors to this method. A study by Texas Tech and Pfizer debunks the resistance argument. The researchers created Safe-guard® (fenbendazole) resistance in a herd of quarter horses. Through a rotational deworming program every two months, alternating ivermectin, fenbendazole, moxidectin and pyrantel pamoate, Safe-guard® resistance was broken.

Rethinking Wormer Rotation

New studies show dewormer rotation may not only be unnecessary, but may also be harmful. Depending on your horse's needs deworming, on a rotational basis, every few months may be excessive and can help parasites breed that are resistant to certain dewormer classes. In a rotating program there could be masked resistance to a given class of dewormer. However, since the other dewormers in the rotation could be working properly you are not aware of this masked resistance.

By rotating dewormers there is also the possibility you could be reducing refugia in your horse. Refugia are parasites left untreated that lack resistance genes. Therefore, when a dewormer is required the refugia will be susceptible to treatment. Rather than having the calendar tell us when we should deworm our horses and with what drug class to use, we need to rely on what our horse tells us through fecal egg count.

Equine Fecal Egg Counts

The best way to determine your horse's deworming needs is through performing a fecal egg count on a sample of your horse's manure. This test will identify which parasites are present in your horse and whether your horse is a high, medium and low shedder. The results will help you and your veterinarian determine an appropriate deworming schedule for each horse. If you are concerned about dewormer resistance, you can also have a fecal sample analyzed 10-14 days after the dewormer was used to identify any resistance issues. Regardless of whether you rotate or not, fecal egg counts are another tool in your arsenal of developing the best parasite prevention program for your horse.

Parasite Management We Can All Agree On

As we have learned there is no cut and dry method for parasite management in horses. Just as you wouldn't walk down the barn aisle and give each horse the same amount of feed, you need to individualize your parasite management program. However there are some parasite management techniques we can all agree on. Proper pasture management is the first line of defense when it comes to fighting parasites. Therefore we should:

  • Remove manure from pastures on a regular basis
  • Reduce number of horses per pasture thus reducing manure load
  • Rotate pastures to break parasite life cycle
  • Harrow pastures to break up manure then rest for several weeks
  • Deworm and isolate new horses so they don't introduce new parasites to your herd

Work with your local veterinarian to determine the best approach for your horses. He or she will be able to evaluate your current deworming program and let you know what will work best for the horses you care for. By creating a comprehensive management program you can reduce the risk of parasite infection in your horse.

Have additional questions or interested in learning more? Contact one of our Equine Specialists or Find A Local Store today.

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