Researchers Evaluate Treatment for Common Equine Parasites

Researchers Evaluate Treatment for Common Equine Parasites

According to recent study results, owners should perform routine fecal egg counts to determine if certain anthelmintics are effective on specific farms when deworming horses.

Photo: Megan Arszman

When it comes to deworming horses, the "blanket" approach is quickly losing its effectiveness due to drug-resistant parasites. So what’s a horse owner to do? According to results of a recent study by Texas A&M University (TAMU), owners should perform routine fecal egg counts to determine which dewormers are effective on specific farms.

In their study, the TAMU researchers evaluated and compared three dewormers' efficacy on fecal egg count reductions of cyathostomins (small strongyles) and Parascaris equorum (large roundworms) in 30 naturally infected foals from the same Texas farm.

“We used foals because they are the ones who would normally get disease, especially when both cyathostomes and Parascaris are involved,” relayed Joe Luksovsky, MS, diagnostic parasitologist in TAMU's College of Veterinary Medicine.

The team randomly assigned foals to three different treatment groups:

  • Treatment 1: one dose of ivermectin/praziquantel at 0.2 mg/kg;
  • Treatment 2: one dose of ivermectin/prazinquantel at 0.2 mg/kg and pyrantel pamoate at 13.2 mg/kg (given at twice the recommended dose because of past occurrences of tapeworms on the farm) simultaneously; and
  • Treatment 3: fenbendazole at 10 mg/kg for five consecutive days.

To determine the number of eggs per gram, the researchers collected fecal samples at the time of each treatment and every two weeks for up to eight weeks post-treatment. Every two months, foals were randomly reassigned to a different treatment group.

Study results included:

  • Treatment 1 was effective for treating cyathostomins (99.9% egg reduction rate) at two weeks post-treatment, but was ineffective for reducing Parascaris egg counts;
  • Treatment 2 reduced cyathostome egg counts by 99.9% and Parascaris egg counts by 95.8% at two weeks post-treatment;
  • Treatment 3 was effective at treating both Cyathostomins (95.8%) and Parascaris (99.9%)after two weeks; and
  • With the exception of Parascaris eggs in Treatment 3, all fecal egg counts increased in Weeks 4, 6, and 8 post-treatment.

In agreement with previous studies, the researchers concluded that, “over time, parasites become resistant to anthelmintics.” They also added that “because there is evidence that one common type of parasite is susceptible to one anthelmintic and resistant to another … a dual wormer approach seems reasonable.”

Luksovsky strongly recommends owners perform fecal egg counts. He stressed, “first and foremost, make sure the dewormer that is being used is actually reducing egg counts.”

The study, “Determining Treatment to Control Two Multidrug-Resistant Parasites on a Texas Horse Farm,” was published in the Journal of Equine Veterinary Science in February. 

About the Author

Casie Bazay, NBCAAM

Casie Bazay holds a bachelor of science degree in education from Oklahoma State University. She taught middle school for ten years, but now is a nationally certified equine acupressure practitioner and freelance writer. She has owned Quarter Horses nearly her entire life and has participated in a variety of horse events including Western and English pleasure, trail riding, and speed events. She was a competitive barrel racer for many years and hopes to pursue the sport again soon.

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