Horses with allergic diseases such as recurrent airway obstruction (RAO) might also have fewer parasites, according to recent research. A new study suggests that genetics might be the primary explanation for this phenomenon.

By investigating RAO and parasite infestations in a family of horses sharing the same bloodline, scientists were able to determine that evolutionary genes which help ward off parasites might also be responsible for susceptibility to allergies. The study, led by Vincent Gerber, DVM, PhD, Dipl. ACVIM, ECEIM, head ad interim of the equine clinic of the department of veterinary clinical sciences at the University of Bern, focused on 73 direct descendants of a RAO-affected stallion and 73 unrelated pasture mates of these horses.

What they found was that the RAO-affected family members were six times more resistant naturally to intestinal parasites than RAO-negative family members, according to the study. Furthermore, the pasture mates, living in identical environmental situations as the family group, were 17 times more likely to harbor parasites than the RAO-affected family members.

"It seems to be some sort of evolutionary advantage that these horses developed genetically," Gerber said. "But with modern environments, stabling, hay-feeding, frequent deworming, and so forth, the downside of the genes--having hypersensitivities like RAO--may be outweighing the upside."

Additionally, their study revealed that horses younger than 10 years old were more prone to parasites than older horses. However, other factors, such as sex, breed, and pasture management, did not cause any significant differences among the infestation rates, Gerber said.

"It appears that the worms are modulating the immune response, and the immune system has somehow become dependent on a presence of worms in order to fully mature," said Martin K. Nielsen, DVM, PhD, equine parasitologist and assistant professor in the department of large animal sciences at University of Copenhagen. "It's very interesting, and we need more studies to understand this phenomenon better."

Nielsen and Gerber said owners should be careful to not try to draw premature conclusions from this research, which is still in very early stages. "This study raises lots of topics for discussions in the scientific community," Nielsen said. "But owners will have to wait (for applications) until we understand the mechanisms between worms and the equine immune system better."

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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