Swiss Researchers Encourage Modern Parasite Control Methods

Swiss Researchers Encourage Modern Parasite Control Methods

Less than 8% of fecal samples from adult horses managed with the "check-before-treat" program indicated a need to actually deworm the horse.

Photo: iStock

Getting horse owners to evolve in how they manage equine intestinal parasites is critical for reducing the risk of anthelmintic resistance—but it’s also a complicated endeavor. The scientists behind new nation-wide programs in Switzerland, however, are leading the way in effecting change. By involving researchers, veterinarians, stable owners, and horse owners in their check-before-treat program, scientists are finding parasite burdens at record lows.

Recent verifications have shown that, within the horse population that’s managed according to the program, less than 8% of fecal samples indicated a need to actually treat the adult horse (at least three years old) with a dewormer. And that, the researchers said, is excellent news.

“Owners are more and more convinced by the approach and the thinking behind a check-before-treat system,” said Hubertus Hertzberg, PhD, researcher at the University of Zurich Vetsuisse Faculty Institute of Parasitology and head of parasite monitoring at HealthBalance, a private holistic animal management and veterinary practice, in Niederuzwil, Switzerland. Here, Hertzberg leads a team entirely focused on equine parasite management.

“The owners don’t want unnecessary, costly treatments, and they like to contribute to the combat against anthelmintic resistance,” he said. “It’s also better on an ecological level, since anthelmintics are shed on pasture, which can disturb the ecosystem. And they see that their horses remain healthy with much less drug input compared to the previous system.”

Hertzberg’s system, now widespread across Switzerland, uses the same schedule as traditional rotational deworming—four times per year. The difference is that instead of blanket-treating all horses every season, the scientists carry out fecal egg counts on each horse. Horses with fewer than 200 strongyle eggs per gram (epg) of feces (and no other harmful parasite infection detected) receive no treatment. As a “security” measure, however, all horses receive a blanket anthelmintic treatment at the end of the grazing season (fall).

In the other seasons, horses receive treatment if their strongyle egg count goes over 200, or if the samples show any signs of the presence of Parascaris spp, Strongylus spp, or cestodes (flatworms). In a recent analysis in the monitored stables, Hertzberg found that the average strongyle egg count among nearly 6,000 samples from adult horses was a low as 57 epg.

But researching that low parasite burdens comes from research and veterinary involvement in the earliest stages, he added. Epidemiological studies—determining the starting rates with respect to the spectrum and intensity of infections—are critical for going forward. So is having a veterinarian overseeing the program to take various parasite-related factors into consideration when developing a strategy for a particular site.

“Our studies have revealed that in some farms, there are strong deficits concerning the role of vets in parasite management,” said Hertzberg, who himself oversees 1,100 horses’ parasite management. “Very often it’s the stable managers or horse owners who determine what is used when. But it’s very urgent to get veterinarians moved back into the center of parasite control.

“The veterinarian has a responsibility to develop control strategies tailored to the requirements of every specific stable and adapting the intensity of treatments to the prevailing husbandry conditions (mirrored by egg counts),” he continued. “It’s very important to obtain detailed knowledge about the epidemiological situation at the farm (with a mandatory visit) and to discuss all items which are related to parasite development with the managers and owners. For example, it’s not only important to know how many hours a horse spends on pasture daily, but what the percentage of roughage obtained from pasture is by this horse (versus hay/silage), as only green forage is able to transmit strongyles.”

In Switzerland, check-before-treat programs began after equine clinicians and parasitologists from the universities of Zurich and Berne, led by Hertzberg, published official veterinary guidelines on selective treatments in 2011.

“Since then, all major players in the country (including some industry partners) have adopted this system,” he said. “That makes it much more convincing for the owners and veterinarians, compared to just hearing and seeing different opinions from various places.”

A current survey indicates more than 50% of the Swiss horse stables partly or entirely rely on the selective treatment approach, starting from virtually zero a few years ago, he added.

The concept of a 200-epg threshold was not easy for many owners to accept at first, Hertzberg said, as most owners feel like their horses should be entirely free of parasites. That, however, is an unrealistic goal.

“We’re helping owners accept the co-existence of host (the horse) and parasite, which is the normal situation in all pastured animals,” he said. “The parasite-free horse is utopic—even in the “old” (seasonal deworming) system. The healthy adult horse is able to manage a basic burden of small strongyles without risk. To teach the owners that their horse is able to live with a certain burden of parasites is not an easy message, but the horses harbored these parasites in the previous strategy as well! It’s just that nobody ever looked at them. No drug is 100% effective, especially against the larval (mucosal) stages.”

Hertzberg said he and his team are now focusing on reassessing parasite control for horses during the first three years of life.

“Here, the higher susceptibility for heavy parasite burdens and therefore the need for more frequent treatments enlarges the risk for generating resistant parasite populations, which will subsequently be transferred from the breeding facilities into the stables,” he said.

But Hertzberg said that, due to promising results, his team is optimistic that “smart monitoring” programs will enable a considerably lower treatment intensity in young horses, as well, and thus will mitigate anthelmintic resistance development.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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