Martin Nielsen, DVM, PhD, EVPC, assistant professor in the Department of Veterinary Science at the University of Kentucky Gluck Equine Research Center, received a one-year grant from the Grayson-Jockey Club Research Foundation to study the interaction between anthelmintic treatment and vaccines.

The study will generate useful information about the interaction between deworming and vaccination in horses. The presence of intestinal worms and the host reaction to deworming can potentially influence vaccination effects through modulating inflammatory reactions in the horse. In addition, the study allows Nielsen to evaluate possible differences between two types of dewormer (ivermectin and pyrantel pamoate) in their effect upon vaccination responses.

Well-managed equine establishments deworm and vaccinate their horses against infectious agents on a routine basis—sometimes having a veterinarian administer both dewormer and vaccination(s) during one visit. Until recently, practitioners considered this to be unproblematic, but recent findings have raised concerns whether the horse's response to deworming might affect vaccination efficacy. Deworming causes a mild and transient inflammatory reaction in the horse, which appears to depend on the type of dewormer used. In addition, intestinal worms have been shown to possess properties capable of modulating an inflammatory response.

In the grant proposal, Nielsen said, “Deworming has been found to cause disease in newly dewormed horses, but usually the inflammatory reaction is mild with no apparent symptoms. However, it is unknown whether this reaction can possibly affect the result of vaccination. Our hypothesis is that deworming causes an inflammatory reaction that affects the response to vaccination.”

In the study Nielsen will evaluate three groups of ponies. Each will receive different vaccinations. He will deworm two of the groups with two different dewormers (pyrantel pamoate and ivermectin) at the time of vaccination and maintain the third group as an untreated control. He will then monitor the ponies for 60 days to evaluate deworming effectiveness, inflammatory response, and generation of vaccine-specific antibody levels.

“This allows us to measure the effectiveness of the deworming, the antibody response to the vaccine, and the inflammatory reaction to vaccination with and without the accompanying deworming,” Nielsen said.

Grayson-Jockey Club Research Foundation will fund 17 projects in 2013, totaling $874,024. The research includes the launch of 12 new projects, continuation of five projects entering their second year, and three Storm Cat Career Development Awards. For more information on all the grants, visit

Jenny Evans, a MFA candidate, is the Gluck Equine Research Foundation coordinator at the Gluck Center.

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