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Get a horse’s weight before deworming for effective, sustainable parasite control

Leave the weight-guessing game for carnivals. A weight tape – or better yet, a scale – helps ensure equine deworming effectiveness and prevents parasite resistance.

“In general, almost all of us are not very good at estimating the weight of our equine patients,” says Kenton Morgan, DVM, managing veterinarian, Equine Technical Services with Zoetis. “Even with experienced people, our estimates are not as good as we think they are. Ideally, we’d weigh horses on a scale, but that’s not always practical.”

Weight tapes are a simple, popular tool that allow veterinarians and horse owners to more accurately assess a horse’s weight, which helps provide the effective dose of parasite control product.

Accurate dosing helps the product work effectively and lessens the opportunity to create anthelmintic resistance. Slowing the process of resistance can help manufacturers, distributors and horse owners retain access to effective and affordable products for years to come.

What contributes to resistance

“Parasite control products are intended to help rid the animal of parasites,” Morgan explains. “When we chronically underdose a horse, it contributes to the selection of resistant parasite populations and accelerates the development of resistance.”

Headshot of Dr. Kenton Morgan
Dr. Kenton Morgan

Deworming too frequently can cause parasites to be overexposed to certain active ingredients, which can also accelerate the development of resistance.

Ultimately, this results in fewer effective treatment options. An effective deworming program is critical for the health of horses – especially considering that over 90 percent of equine internal parasites like small strongyles, tapeworms, pinworms, roundworms, bloodworms and threadworms reside in the environments that horses are exposed to every day.

Slow resistance, retain effectiveness

For distributors, slowing the development of resistance helps retain the effectiveness of this important category.

“There are a finite number of deworming products out there,” Morgan says. “There aren’t new products on the horizon so we have to make the most out of what we have on hand. Most of these products are several decades old. It’s everyone’s responsibility to use them judiciously and appropriately. It’s better for the horse and prolongs the effective lifespan of these products in the marketplace.”

In addition to accurate dosing, Morgan advises distributors to recommend appropriate seasonal timing for parasite control products and fecal egg counts with a local veterinarian.

Watch out for breed differences

The accuracy of a weight tape can vary depending on the horse’s breed and even the season. For example, a horse with a heavy coat of winter hair can return a heavier weight when a weight tape is used.

Weight tapes tend to be more accurate in Quarter horse breeds compared to Thoroughbreds or Warmbloods.

“If you marginally overdose a horse, it’s less of a safety concern with all the currently marketed anthelmintics,” Morgan notes. “It doesn’t make a product more effective to overdose it – there’s no real advantage, and it costs the owner more money.”

All approved anthelmintics for horses are safe, Morgan says.

“It’s important for horse owners to understand that deworming treatment doses are based on the weight of the individual horse. Eyeballing a horse’s weight is risky, as underdosing can contribute to resistance. Using a weight tape or scale eliminates the guessing game and ensures an accurate dose for your horse.”

  • • Inaccurate dosing of dewormers can cause parasites to be overexposed to certain active ingredients, which can cause them to become resistant.
  • • Slowing the development of resistance can help ensure optimal horse health and preserve the effectiveness of dewormers.
  • • Weight tapes have drawbacks, but are a simple and affordable way to get a more accurate weight before administering dewormers.
  1. 1. Ensure the horse is standing square.
  2. 2. Place the weight tape around the horse’s heart girth. For consistency, use the same weight tape and follow the instructions which accompany the tape.
  3. 3. Read the number where the tape meets for the closest weight approximation.
  4. 4. Set the dewormer to the correct weight to administer an accurate dose.

To ensure an effective deworming treatment, begin with a fecal egg count test and then capture the horse’s accurate weight before administering the parasite control product.