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Training Time Affects Gene Expression in ThoroughbredsBy Kentucky Equine Research Staff · September 15, 2011
Thoroughbred racehorses rarely train at the same time of day as they race. Conventional wisdom dictates that muscle adaptions resulting from morning training translate into racing performance in the afternoon. New research from Ireland suggests this may not be the case.
Using six three- or four-year-old mares, researchers at the University College Dublin examined if synchronization of muscle-specific, performance-related genes occurs in equine skeletal muscle in response to a set training time. Muscle biopsies were harvested from the mares at four-hour intervals over a 24-hour period. The mares then began an eight-week midmorning training program, with a gradual increase in exercise intensity each week. At the end of the eight weeks, muscle biopsies were collected from each mare again at four-hour intervals over a 24-hour period. The expression of a number of genes involved in muscle metabolism was measured in the biopsy samples.
Genes that are responsible for muscle metabolism are expressed or “turn on” at various times of the day and the timing of certain gene expression is affected by when the horse normally trains. For instance, the researchers found that a gene involved in the development of muscle (MYF6) is expressed at night corresponding to a time of muscle regeneration and repair. Other genes express around the time that the horse typically exercises. In this study, the UCP3 gene, which plays a role in the protection of muscle from oxidative damage during exercise, had a peak expression in the morning prior to scheduled exercise. This suggests an anticipatory muscle defense mechanism. It was found that another important muscle gene (PDK4) was also expressed in response to training time. PDK4 is highly associated with elite racing performance. This study suggests that performance may be enhanced when training and competition times coincide.
This study was presented at the 2011 Equine Science Society Symposium in Murfreesboro, Tenn. The proceedings from this symposium are available from the Journal of Equine Veterinary Science.
