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New Deworming Strategies

Parasites are becoming resistant to some of the common dewormers, prompting the American Association of Equine Practitioners to revise their guidelines and recommend a targeted, need-based treatment approach based on fecal egg counts. Many horses naturally have little to no worms, while others may have very high worm egg counts. When you submit a sample for a fecal egg count, your horse will be classified as a "low egg shedder", "medium egg shedder", or "high egg shedder". Only about 20% of the horses in a given herd carry 80% of the worms, which means that the other 80% of the herd is likely being dewormed too often, and the 20% with the majority of the worms will need to be dewormed more often.

After the fecal egg count is performed, you will receive a customized deworming plan for your horse based on the results. This report will outline the correct products to use at the correct times of year based on your horse's specific results. This individualized plan will prevent your horse from being dewormed too often or not enough and will help combat the emerging resistance problem.

A fecal egg count should be performed on each horse at least once a year to accurately determine an effective deworming plan. Additional fecal egg counts can be performed to detect if the worm population on your farm has developed resistance to any of the common dewormers. This involves taking a manure sample before deworming and then 10-14 days after deworming to measure if the product used was effective. If resistance is detected, that product should not be used on that farm because it no longer works.

Timing for collecting a manure sample:

When performing a fecal egg count, it is important to wait the correct amount of time after the last dewormer was administered. Please use these guidelines so that the dewormer does not interfere with the results.

After Moxidectin (Quest or Quest Plus), wait at least 16 weeks to collect a fecal

After Ivermectin (Bimectin, Zimectrin), wait at least 12 weeks to collect a fecal

After Fenbendazole or Oxibendazole, (Panacur, Safe-Guard, Anthelcide), wait at least 9 weeks to collect a fecal

After Pyrantel (Strongid or Exodus), wait at least 9 weeks to collect a fecal

A fecal test should be performed on each horse at least once a year to determine the deworming strategy for the next year. A great time to perform a fecal egg count is in the spring before the horse is dewormed. Samples can be collected and given to the veterinarian at the time of spring vaccinations, or they can be dropped off at the office.

How to collect the manure sample:

- Fresh manure is important, as eggs deteriorate with time and temperature. Ideally, collect the sample soon after the manure is passed. If the pile looks like it has been passed within a few hours, collect the sample from the middle of the pile.

- Collect 1-2 fecal balls of manure in a ziplock bag and label with the horse's name.

- Keep the sample refrigerated or with an ice pack until it is submitted. Room temperature is fine if you are bringing the sample right away. Do not leave it in direct sunlight or store it in a hot car.

-Samples can be picked up by the veterinarian at the time of spring vaccinations, or they can be dropped off at the office. Leaving horses in stalls for a couple hours before the spring vaccination appointment will likely produce fresh samples for when the veterinarian arrives.

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