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One area of interest in human medicine has been the potential anti-inflammatory effects of dietary polyphenols. Polyphenols are naturally occurring compounds found in plants, particularly in fruits, vegetables, tea, and herbs. They act as antioxidants and modulators of inflammatory pathways. In human asthma, certain polyphenols have been reported to reduce airway inflammation and improve lung function. Despite this promising background, their application in equine asthma had not been previously explored.
Researchers from the Department of Large Animal Medicine at the University of Georgia set out to investigate whether dietary polyphenol supplementation might offer similar benefits in horses with EAS. Their study aimed to evaluate the effects of a mixed polyphenol supplement on both systemic and pulmonary inflammation, as well as on bronchoalveolar lavage (BAL) cytology and clinical respiratory signs in healthy and asthmatic horses. The team hypothesised that polyphenol supplementation would decrease inflammation in both groups, and in asthmatic horses, would also lead to improvements in BAL cytology and respiratory signs.
The research was conducted in two parts.
Part One:
Eighteen horses were enrolled, including eight healthy horses and ten with asthma. Each horse received the polyphenol supplement daily for 6–8 weeks. Before and after supplementation, the researchers performed a thorough physical examination, collected BAL fluid, and measured cytokine concentrations in both serum and BAL fluid.
Findings: Horses with mild-to-moderate asthma showed improved BAL cytology after supplementation. In particular, the percentage of neutrophils (a marker of airway inflammation) decreased significantly in the asthmatic group. Levels of pro-inflammatory cytokines, including interleukin-6 (IL-6), also decreased after supplementation. Interestingly, interleukin-10 (IL-10), typically considered an anti-inflammatory cytokine, also showed a greater reduction in asthmatic horses compared with healthy ones, though the functional significance of this is not yet clear.
Part Two:
Ten asthmatic horses were divided into two groups: five received the polyphenol supplement, and five served as unsupplemented controls. All horses were maintained on a low-dust diet for four weeks, after which airway inflammation was deliberately exacerbated by feeding dusty hay for another four weeks. Throughout, the team assessed clinical signs, rebreathing examination findings, and pulmonary inflammation.
Findings: Supplemented horses demonstrated clear clinical benefits. They had significantly lower respiratory rates than controls during the dusty hay challenge, and fewer supplemented horses showed abnormal findings on rebreathing examinations. These improvements occurred despite evidence of ongoing airway inflammation, suggesting that supplementation may have helped to blunt the clinical impact of the environmental challenge.
The polyphenol supplement was well tolerated and readily eaten by horses when fed as a top-dressing, making it a feasible option in practice. Importantly, supplementation was not presented as a replacement for environmental management but rather as an adjunct. Controlling dust exposure, optimising ventilation, and feeding low-dust forages remain the cornerstone of asthma management in horses. However, dietary polyphenols may provide additional support by modulating inflammatory processes at both systemic and pulmonary levels.
This research provides preliminary evidence that dietary polyphenol supplementation can reduce airway inflammation markers and improve clinical signs in horses with mild-to-moderate equine asthma. While further work is needed to establish long-term effects, optimal dosing, and the mechanisms involved, polyphenols represent a promising area of nutritional support for respiratory health in horses.
For more details, see:
K.M. Andrews, L.J. Berghaus, K.A. Hart,
Effects of mixed polyphenol supplementation on lower airway inflammation in horses with Equine Asthma Syndrome,
Journal of Equine Veterinary Science,(2025) Vol 154,105681,
