Researchers Discover Stress Genes in Racehorses

Edited Press Release

Scientists at University College Dublin and Plusvital Ltd. in Ireland have published a study describing the discovery of genes in racehorses that are associated with stress and coping in the training environment. The research, which is titled “Integrative genomics analysis highlights functionally relevant genes for equine behaviour,” appears in the peer-reviewed journal Animal Genetics and is the result of a four-year PhD research project that examined the stress hormone cortisol and the results of a questionnaire in 100 yearlings as they encountered key milestone events during the early training period.

“The most stressful event for a young racehorse is the first time it is backed by a jockey, with studies showing that it causes the greatest cortisol response in the horse,” lead scientist Dr. Amy Holtby said. “Some horses cope better than others, with lower cortisol reactions,”.

One key finding was that yearlings’ behaviour with highly experienced handlers did not agree with the cortisol results, indicating that cortisol identifies a distinct aspect of the stress response that is not perceivable to handlers.

“This means that some horses experience stress without acting out, and this could have detrimental long-term effects if it cannot be managed appropriately,” senior scientist Professor Emmeline Hill said. “Identifying genetic markers for the stress response could
therefore have value in identifying horses most susceptible to stress.”

The scientists compared the genetic profiles of the yearlings in early training best able to cope with those less able to cope. They used genetic data from two different brain tissues that regulate the fear response and the modification of behaviour to pinpoint the genes that were most likely to impact on the ability to cope. This approach highlighted a set of genes that function [in other species] in social behaviour, suicide, stress- induced anxiety and depression, neurodevelopmental disorders, neuroinflammatory disease, fear-induced behaviours, and alcohol and cocaine addiction.

The gene that was most important in the Thoroughbred stress response was NDN (necdin), which is associated with temperament in cattle and measured as ‘flight time’ (the time taken for an animal to reach a fixed distance following release from an enclosure). In humans this behavior is associated with paranoia.

“Everyone involved with racehorses recognises the importance of maintaining the mental well-being of their animals and balancing the training routine to keep them happy and engaged with their work,” Dr. Holtby said. “It is one of the most crucial aspects of

Professor Hill added, “Genetics doesn’t have all the answers, but our research provides a sound scientific basis for genetic screening tools to support the highest welfare standards for the Thoroughbred. The ‘nurture’ aspect of behaviour is of course a major factor, with the management of the animal impacting on its temperament. Our research has revealed genetic markers that could be used to identify animals that will benefit most from more nuanced handling. In time these makers could also be developed into tests to inform breeding decisions.”

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