Equine researcher presents work on heaves-related gene search

The 16th annual Plant and Animal Genetics conference held January 12-16 at the Town and Country in San Diego included a January 13 equine workshop in which an English equine geneticist addressed her work on mapping genes associated with heaves.

June Swinburne of the Animal Health Trust located in Newmarket was the presenting author of “Mapping Genes Associated with Recurrent Airway Obstruction in Horses.”

Other Animal Health Trust researchers included Sarah Blott, Helen Bogle, Elizabeth Temperton, and Mark Vaudin, and the research also involved University of Berne researchers Jolanta Klukowska, Tosso Leeb, and Vincent Gerber.

Funding was provided by the United Kingdom’s Horse Trust, the Swiss National Science Foundation, and Vetsuisse.

Recurrent Airway Obstruction, also known as RAO or “heaves,” is an inflammatory airway disease which results in coughing and exercise intolerance due to increased mucus production and narrowing of the airways.

“This condition results in ineffective breathing,” Swinburne said.

The breathing difficulties cause flared nostrils and a heaving flank. In severe cases RAO is treated with aerosolized corticosteroids and bronchodilators.

RAO is influenced by environmental conditions but caused in part by inherited factors. “This condition is initiated or aggravated by airborne dust,” Swinburne said.

Heaves is also considered to be a possible model for human asthma. “This is a chronic condition,” Swinburne said. “This condition is very similar to human asthma.”

The relative risk of RAO is increased in horses with at least one affected parent, although the disease is inherited equally from both parents. The relative risk factor is 3.2 when one parent is affected and 4.6 when both parents have the condition. “It’s due to a genetic susceptibility,” Swinburne said.

Swinburne and her group studied two half-sibling families of Swiss Warmblood horses. One sire provided 132 horses to be sampled while the other sire contributed 98 horses to the study.

A questionnaire was sent to owners to obtain information on the horses’ histories of coughing, respiratory distress, increased breathing effort after exercise, and nasal discharge. The information was compiled into a Horse Owner Assisted Respiratory Signs Index (HOARSI) which used a scale of 1 (healthy) to 4 (severe).

A genome scan was performed using 252 microsatellites in order to locate genes influencing RAO. “We’re going to map these regions we’ve identified,” Swinburne said.

Additional microsatellites are currently being studied. “We’re putting more microsatellite markers into these regions,” Swinburne said. “We hope that will increase the signal.”

Further plans include collecting data from unrelated Swiss Warmblood horses and from other breeds to confirm the impacted chromosome regions. “Hopefully we’ll eventually identify the genetic variants that contribute to the disease,” Swinburne said.