Respiratory disease is common at equestrian shows and events. This highlights how difficult it is to recognize horses that are silent carriers of pathogens. That means owners need to use good biosecurity with their horses at shows and events.

A study was published in February 2025. It looked at non-clinical (healthy) racehorses and show horses to determine the frequency of shedding of respiratory pathogens before and after exercise. The study was titled, “Investigation of the role of exercise in the detection of selected respiratory pathogens from nose wipes collected from healthy horses.” It was authored by Cara A. Wright, K. Lawton, S. Barnum, B.W. Craig, B.R. Farwell, J. Blea, C. McCook, and N. Pusterla.

Introduction

The researchers noted that currently, shows and events focus on recognizing and isolating sick horses. They stated that little attention is dedicated to testing healthy horses. “Previous studies have highlighted the importance of silently infected horses, especially regarding equine herpesvirus (EHV)−1 and Streptococcus equi spp equi (S. equi), as a potential source of infection.”

These researchers noted the fact that horses are averse to nasal swabs. (Editor’s note: Think large Q-Tips stuck up the horse’s nose.) They noted that prior research has shown that less invasive nasal wipes were just as effective as nasal swabs in collecting samples of EHV-2 in yearlings.

Therefore, “the aim of the present study was to determine if exercise increases the frequency of selected respiratory viruses/bacteria shedding in non-clinical horses using nose wipes.”

Study Information

In the study, nose wipes were taken pre- and post- exercise from 133 healthy horses of various ages and disciplines. The wipes were assayed for the presence of selected common respiratory pathogens. Those included equine herpesvirus-1 (EHV), EHV-4, S. equi spp equi, plus EHV-2, EHV-5, and S. equi spp zooepidemicus.

Samples were collected at three racetracks in California, Oklahoma, and Maryland and three show horse training barns in California. The sampling collections were performed in April and May of 2024. Disposable gloves were worn and changed for each sample collection. Routine exercise depended on the discipline and consisted of a minimum of 10-15 minutes of trotting or galloping.

The study included 33 horses ag 2 to 20 years. The researchers said age varied by discipline. They included 43 show horses (hunter/jumper, dressage). Those horses ranged in age from 5 to 20 years. The 90 racehorses had an age ranging from 2 to 9 years.

The horse breeds included in the study were 63 Thoroughbreds, 28 Quarter horses, 25 Warmbloods, 15 ponies, and 2 Lusitanos. All Thoroughbreds and Quarter horses were used for racing, while the Warmbloods, ponies, and Lusitanos were used for shows.

Findings

The study results showed that exercise increased the detection frequency of EHV-1, EHV-2, EHV-5, and S. zooepidemicus in nose wipes collected from non-clinical horses. 

“Racing horses displayed a higher frequency of EHV-2, EHV-5, and S. zooepidemicus detection when compared to show horses,” the researchers noted. “Differences in demographic and husbandry may have accounted for these differences as gamma herpesviruses are more likely to circulate amongst young horses compared to older horses.” 

The high detection rate of EHV-1 in racing horses was unexpected, the researchers stated. That was because respiratory disease was not reported in these horses. The researchers said that highlights “the high frequency of silent EHV-1 shedders in young horses.” 

“In conclusion, the results of this study showed that exercise increased the frequency of detecting EHV-1, EHV-2, EHV-5, and S. zooepidemicus in non-clinical horses using nose wipes,” stated the researchers. “Nose wipes appear to be an effective method of collecting samples in healthy horses, increasing compliance and acceptance of horses during sample collection. Future studies should include direct comparison of nose wipes with the reference standard of nasal swabs or guttural pouch lavages in the case of S. equi. Such protocols need to be further investigated in the field and compared to pathogen-specific reference standard samples.”

Highlights from the Research

  • Exercise increases the frequency of finding certain respiratory organisms (equine herpesvirus (EHV)- 1, EHV-2, EHV-5, and S. zooepidemicus.) in healthy horses.
  • EHV-4 and S. equi were only detected in a small number of horses post-exercise. Interestingly, the only positive S. equi detections were after exercise.
  • The absolute quantitation of pathogens was significantly lower post-exercise (p < 0.05) for EHV-2, EHV-5, and S. zooepidemicus.
  • Nasal wipes appear to be an effective method of collecting samples in healthy horses.

Further Reading

  • Kimberly S. Brown
    Kimberly S. Brown is an award-winning writer and publisher. She is the Editorial Director for My Senior Horse. Brown spent 10 years at Equine Network, parent company of My Senior Horse. Prior to that she worked for three years in equine nutrition after she retired from nearly 30 years working at The Blood-Horse. Brown spent the last 15 years of her time at that organization creating and developing The Horse and TheHorse.com.
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