Researchers Delve into Genetic Basis of Equine Asthma

In its mildest form, equine asthma negatively affects performance due to airway inflammation, coughing, and nasal discharge. In severe manifestations, asthmatic horses suffer exercise intolerance and often struggle to breathe at rest. Current treatments only help control airway inflammation and coughing, underscoring the need for new treatment options.

According to the most recent veterinary guidelines, medications for asthma include bronchodilators to counteract airway constriction and corticosteroids for anti-inflammatory effects.^*

“Long-chain polyunsaturated fatty acids, like those found in EO-3, may also help control inflammation and are recommended by asthma experts,” noted Ashley Fowler, Ph.D., a nutritionist at Kentucky Equine Research.

Even when combined with environmental management to limit exposure to dust and inhalable particles, many horses continue to suffer from asthma.

To devise more effective treatments for asthma, an improved understanding of how this disease develops at both a cellular and genetic level is necessary. One way to pinpoint exactly how a disease such as asthma manifests is to identify, measure, and compare genes that are changed—either expressed at a higher level or inhibited—in healthy and sick patients. This process is called transcriptomic analysis. This laboratory technique can also help identify potential therapeutic targets that may help treat affected animals.

Italian veterinary researchers recently used transcriptomic analysis to learn more about equine asthma.^** They identified eight horses with severe equine asthma (SEA), ten with mild equine asthma (MEA), and seven healthy control horses. All horses had bronchoalveolar lavage performed, a test that involves infusing a small volume of saline into the horse’s lungs and then immediately retrieving the fluid in order to analyze recovered cells and other biological materials.

“In this study, the researchers identified over 1,750 genes that were ‘differentially expressed,’ which means that the genes were either ‘turned up’ or ‘turned down’ in horses with equine asthma compared to the healthy control horses,” explained Fowler.

Not only were differences observed between healthy controls and asthmatic horses but also between horses with MEA and SEA.

Of those 1,750 genes, the following changes in expression were believed to be the most clinically relevant:

• Genes involved in the growth, length, and function of the airway cilia were downregulated in horses with mild or severe asthma. Cilia are fingerlike projections found inside the airways that help clear mucus and debris out of the lungs and airways;
• A significant increase in genes involved in inflammation was identified in horses with MEA; and
• Genes playing a role in airway constriction and cell death were upregulated in samples collected from horses with SEA.

According to the researchers, this data “contributed to the advancement of our understanding of the pathogenesis and the immunological mechanisms underlying equine asthma.”

Further evaluation of these genes may help identify candidate therapeutic targets to help owners better treat affected horses.

“Innovative therapies targeting specific cellular pathways might reduce clinical symptoms in SEA-affected animals and, for MEA-affected horses, allow a quicker return to competition,” the research team suggested.

^*Couëtil, L.L., J.M. Cardwell, V. Gerber, J.-P. Lavoie, R. Leguillette, and E.A. Richard. 2016. Inflammatory airway disease of horses—Revised consensus statement. Journal of Veterinary Internal Medicine 30(2):503-515.

 ^**Padoan, E., S. Ferraresso, S. Pegolo, C. Barnini, M. Castagnaro, and L. Bargelloni. 2022. Gene expression profiles of the immuno-transcriptome in equine asthma. Animals (Basel) 13(1):4.