Effects of racing and nontraining on plasma thyroid hormone concentrations in sled dogs

摘要

Sled dogs competing in the Iditarod Trail Sled Dog Race perform prolonged endurance exercise in cold conditions, often traveling > 100 miles/d for 8 to 12 days while pulling a laden sled. This activity is associated with an extraordinarily high metabolic rate, and sled dogs expend > 10,000 kcal/d during racing. The thyroidal hormonal changes associated with such highenergy expenditures and endurance racing have been reported to a limited extent. In a previous study, lower plasma thyroxine (T_4) concentrations in sled dogs competing in a long distance race, compared with values before racing, were reported, and values were often lower than the reference range for nonsled dogs. However, the number of dogs in that study was small, and concentrations of free T_4 (fT_4), thyroid-stimulating hormone (TSH), and thyroglobulin auloantibody (TgAA) were not measured. Therefore, the effect of racing on thyroid hormones in sled dogs has not been adequately determined.