Parasite Egg Shedding on Central Kentucky Horse Farms

Parasite Egg Shedding on Central Kentucky Horse Farms

The researchers considered management aspects as part of the reason why Thoroughbreds and Standardbreds had lower levels of parasite infection compared to the smaller group of mixed light breeds.

Photo: Anne M. Eberhardt/The Horse

Researchers from the University of Kentucky Gluck Equine Research Center recently conducted a study on strongyle parasite egg count values in horses on 25 Central Kentucky farms. Data from the study showed the benefit of establishing strongyle egg counts to determine the need for treatment.

The trend for parasite control in horses has long been to deworm on a frequent basis, although it is well-known that this might lead to widespread drug resistance. Typically, owners treat herds without first performing parasite egg counts to help determine which individual horses need treatment.

Therefore, the researchers aimed to investigate the strongyle egg count status on a large number of horses on a regular deworming program, said Gene Lyons, PhD, professor in classical parasitology at the Gluck Center.

A total of 1,300 mares of various ages participated in the study (most were Thoroughbreds, while the rest were Standardbred and mixed light breeds). The goal was to establish a strongyle egg count profile on each mare based upon age, number of egg count positives, and level of egg shedding.

“Findings from the study clearly showed the value of performing the EPG (eggs per gram) status on horses. The most important result of this research was that the majority of Thoroughbred and Standardbred mares had no or low egg counts. Since these horses were already on a regular deworming program, there would be no obvious reason to give them extra treatment," Lyons said.

Upon reviewing the results of this particular study, the researchers also found:

  • The Thoroughbreds had the lowest prevalence of positive egg counts at 32%. The youngest age group (3-5-year-olds) showed the highest strongyle counts, while the group of 6-10-year-olds and older had lower infection rates.
  • 48% of the Standardbreds were positive for strongyle egg count. For both Thoroughbreds and Standardbreds about 60-70% of horses had low egg counts below 200 eggs per gram (EPG).
  • In contrast, 77% of the mixed light breed mares were positive for egg count. The infection rates for this group were highest in 3-10-year-olds and lowest for the older age groups, but significant for all the age groups. More than 37% of the mixed light breed mares had values of more than 500 EPG.

The researchers considered management aspects as part of the reason why Thoroughbreds and Standardbreds had lower levels of parasite infection compared to the smaller group of mixed light breeds.

The mixed light breeds tended to graze on more overpopulated pastures with less intensive management, whereas the Thoroughbreds and Standardbreds tended to have ample pasture, Lyons said. All breeds were on a routine deworming schedule, and the research team therefore suggested management efforts could influence strongyle egg counts.

“While our data clearly showed that different horse management systems affect the parasitic status of horses, an association between the breeds of horses and the prevalence of parasite infection could not be established,” Lyons said.

Shaila Sigsgaard is an editorial assistant for the Bluegrass Equine Digest.


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More information on Gluck Equine Research Center and UK Ag Equine Programs.

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