Exercise’s Effects on Respiratory Pathogen Detection in Healthy Horses

At the 2025 American Association of Equine Practitioners convention, Nicola Pusterla, DVM, PhD, DACVIM, DAVDC-Equine, professor of equine internal medicine at the University of California, Davis, School of Veterinary Medicine, presented his research on the role of exercise in detecting selected respiratory pathogens.

Risk Factors for Respiratory Infections in Horses

He began by reminding practitioners that stress, transport, co-mingling with conspecifics, lack of biosecurity, age of the horse, vaccination status, and use can predispose horses to infection.

“We can all realize that putting an ill horse beside a healthy horse is high risk,” he added. “What we don’t know is how this relates to subclinical shedders.”

The overall rate of subclinical shedders is highly variable, depending on the respiratory pathogen, population and use of the horses, as well as season.

Study: Role of Exercise in Detecting Respiratory Pathogens

Pusterla and colleagues conducted a study investigating the role of exercise in detecting selected respiratory pathogens, using nose wipes collected from healthy performance horses before and after exercise, when nasal secretions were increased. This was a voluntary study that trainers elected to enroll their healthy horses in at various racing and training locations in spring 2024.

Nose wipes were chosen over more invasive nasal swabs. All nasal wipes were processed for nucleic acid purification and tested for true pathogens (equine herpesvirus -1 and -4, Streptococcus equi subsp. equi), commensals (EHV-2, and -5, S. equi subsp. zooepidemicus), and an endogenous control.

“We compared the frequencies and quantitation for each pathogen in pre- and postexercise samples,” said Pusterla. “We weren’t really expecting too much because the samples were collected voluntarily from healthy horses. But surprisingly, quite a fair number of racing horses had a significant increase in EHV-1 (n = 13) in the postexercise samples.”

A similar increase in postexercise frequency of detection was observed for EHV-2, -5 and S. equi subsp. zooepidemicus.

“We didn’t know what to do with this information because the horses were not clinically affected,” said Pusterla.

Study Findings

They did determine that:  

• Collecting samples via nasal wipes is easier, less invasive, and better tolerated by horses than swabs. 

• Commensal pathogens are ideal to study dynamic rates of shedding in various horse populations. 

• Pathogen frequency varied by horse population (i.e., racing vs. showing). Specifically, racing horses had higher rates of EHV-1, -2, and -5 and S. equi subsp. zooepidemicus than show horses. 

• Exercise increased frequency of pathogen detection in nasal wipes. 

• Absolute quantitation of pathogens reduced with exercise. 

Medical coverage from the 2025 AAEP Convention is brought to you by American Regent Animal Health.

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