New Study Reinforces Notion That Thyroid Supplement May Endanger Fit Horses

by | 03.21.2019 | 5:03pm
A planned harness racing track and casino in Tinley Park, Ill., is on hold

Giving fit horses unnecessary thyroid supplements may cause cardiac arrhythmia, a new study shows. Some trainers give their racehorses Thyroxine to perk them up. The drug is more commonly used on horses that have insulin resistance or Equine Metabolic Syndrome (EMS)—neither of which is found in fit racehorses.

Dr. Janice E. Kritchevsky, with the Purdue University College of Veterinary Medicine, spearheaded the study after reports of open thyroxine containers were found in training barns in Ontario. In addition, elevated concentrations of thyroxine has been reported in the blood of racehorses post-race.

The study used six fit Standardbred horses; it did find a change in behavior once the supplement was administered. While the horses became difficult to handle and very alert, they also grew tired more quickly. The drug was not found to be performance enhancing. Four of the study horses developed an irregular heartbeat when treated with thyroxine; one developed atrial fibrillation, which severely limits performance and can be career ending.

Kritchevsky notes that this supplement does not do what racehorse owners and trainers believe it does; high levels of the drug render the horse unfit to race. Some track officials feel that thyroxine should be a regulated drug and that research should be done to develop an assay to test for a high thyroid.

Read more at HorseTalk.

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