Avoiding Anthelmintic-Resistant Parasites in Working Equids

Avoiding Anthelmintic-Resistant Parasites in Working Equids

Working equids in tropical and subtropical climates might be full of intestinal parasites, but deworming those animals to render them worm-free might not be the best strategy, one research team says.

Photo: Icon Studios Photography/Karen Kennedy

Working equids in tropical and subtropical climates might be full of intestinal parasites, but deworming those horses to render them worm-free might not be the best strategy. According to Mexican researchers, massive deworming might do more harm than good by opening the door for anthelmintic-resistant parasite development.

Miguel Ángel Alonso-Díaz, PhD, DVM, of the Faculty of Veterinary Medicine of the Independent National University of Mexico, in Veracruz, explained that because the number of parasites doesn’t appear related to body condition in individual working horses, mules, and donkeys, treating all affected working equids with anthelminthics might not make a noticeable difference in many animals' health status. It could, however, encourage anthelminthic-resistant parasites in those areas; resistant parasites are already posing a major problem in other regions of the world, Alonso-Díaz added.

“We suggest only deworming the animals that show clinical signs of parasite infection (such as diarrhea, colic, and emaciation), or those with low body condition scores, as a preventive or control treatment,” Alonso-Díaz said. He noted, however, that all the horses should have access to enough good-quality forage and grains, which will help improve their health and immune systems.

In the 140 working equids in central Veracruz that Alonso-Díaz and his fellow researchers monitored during the study, body condition averaged a “moderate” score (about 2.5 out of 5), he said. In horses, specifically, the average score was 2.8. Of all the equids, 90% had parasite infestations and none had been treated for worms in recent months.

On average, horses with more severe parasite infestations did not have lower body condition scores than horses with minor infestations, he said. There was also no relationship between equids' degree of infestation and blood analyses (including red and white blood cell counts, basophils, neutrophils, and lymphocytes, among other values).

“Animals under optimal nutritional conditions have the potential to increase their resilience and/or their resistance to gastrointestinal parasites with affecting body condition,” he said.

Even so, Alonso-Díaz said he believes that parasite infestations can cause a drop in body score, especially if the horse is not fed well enough. In certain parts of Mexico with greater poverty levels, for example, working equids have an average body score of 1.5, he said.

The solution in these regions with these kinds of horses, then, should be to increase food quality and quantity while only treating symptomatic horses, Alonso-Díaz said.

“With this protocol, we expect to avoid anthelminthic resistance and prolong the productive life of the molecules (treatment),” he said.

The study, "Gastrointestinal nematode burden in working equids from humid tropical areas of central Veracruz, Mexico, and its relationship with body condition and haematological values," appeared in Tropical Animal Health and Production in February. 

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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