Training-related inflammatory changes seen in the airways of racehorses

Neutrophilic airway inflammation is prevalent in racehorses in training, with the term mild to moderate equine asthma applied to most cases.
Image by Calvin Tatum

Racehorse training drives a range of immune-related inflammatory changes in the airways of horses, researchers report.

Anna Karagianni and her fellow researchers at the University of Edinburgh noted that neutrophilic airway inflammation is prevalent in racehorses in training, with the term mild to moderate equine asthma applied to most cases.

Their study, reported in the journal Scientific Reports, was prompted by the strong association between mild to moderate asthma in racehorses and their entry into race training.

The researchers set out to explore the effect of training on the local pulmonary immune system by defining the gene and protein expression in tracheal wash samples taken from 16 Thoroughbreds before and after the start of race training.

Samples were collected at two different time points – when the horses were at rest between racing seasons, and when they were in active race training. The horses had, on average, been at rest 59 days when one set of samples was taken. The race-training samples were taken 2.5 months into their exercise regime, at which point they were considered racing fit.

All recruited horses were from the same training yard and were managed the same way.

The authors reported that the tracheal wash samples proved to be a rich source of airway cells, proteins and RNA, enabling them to identify the effects of training on airway innate immune responses at both the gene and protein level.

Their analysis detected 2138 differentially expressed genes and 260 proteins during the training period. Gene and protein sets were enriched for biological processes related to acute-phase response, oxidative stress and haemopoietic processes (blood formation), as well as to immune response and inflammation.

The findings, they said, support a clear association between intense training and immune system deregulations, haemopoietic and metabolic abnormalities, and cellular stress at the airway level.

Overall, the observations were consistent with a level of inflammation in the airways during training – a phenomenon very well documented in racehorses.

“It is conceivable that such training-associated changes may play a role in increasing susceptibility to opportunistic infection and airway inflammation in racehorses.”

The differences found amounted to significant training-associated alterations in both gene and protein expression within the samples, they said.

It was unsurprising that most of the horses (11 out of 16) developed cytological evidence of exercise-induced pulmonary haemorrhage (bleeding into the lungs) during the training period, given the condition’s high prevalence in racing Thoroughbreds.

The findings, they said, likely reflect the known associations between race-training and both airway inflammation and bleeding, offering further insight into the potential mechanisms which underpin training associated airway inflammation.

Their work, they said, could open doors for future research on equine exercise immunology based on a wider, better defined and preferably naïve population entering training for the first time.

“Developing such novel information could have a significant positive impact on Thoroughbred welfare and the racing industry.”

The researchers noted that previous studies had demonstrated a clear association between housing and airway inflammation, reflecting increased exposure to organic dust.

The study horses were housed during the training period, but were largely at pasture during the sampling when at rest.

“It is quite feasible,” they said, “that some of the immunological changes observed, at both the individual gene and protein level and the pathway level, were consistent with an increased exposure to organic dust. However, this was not universally or consistently reflected in the tracheal wash differential cytology data.”

Ventilation within the racing stable was considered good and all horses were bedded on low-dust shavings and fed haylage from the ground.

In line with previous studies, the immunological changes associated with training may have been triggered by the repeated episodes of high-intensity exercise experienced by the horses, the authors said. Researchers in a previous study had shown training-associated changes in immunity at the lower-airway level in treadmill-exercised horses.

They noted that many similarities were observed with human-derived data in relation to exercise immunology, supporting the use of the horse as an attractive animal model from which translational application of findings to humans may be justified.

The study team, all affiliated with the University of Edinburgh, comprised Karagianni, Dominic Kurian, Eugenio Cillán-Garcia, Samantha Eaton, Thomas Wishart and Scott Pirie.

Karagianni, A.E., Kurian, D., Cillán-Garcia, E. et al. Training associated alterations in equine respiratory immunity using a multiomics comparative approach. Sci Rep 12, 427 (2022).

The study, published under a Creative Commons License, can be read here

Latest research and information from the horse world.

Leave a Reply

Your email address will not be published.