Effects of racing and training on serum thyroid hormone concentrations in racing Greyhounds

Objectives-To determine the effects of racing and training on serum thyroxine (T₄), triiodothyronine (T₃), and thyroid stimulating hormone (TSH) concentrations in Greyhounds. Animals-9 adult racing Greyhounds. Procedure-Serum thyroid hormone concentrations were measured before and 5 minutes after a race in dogs trained to race 500m twice weekly for 6 months. Resting concentrations were measured again when these dogs had been neutered and had not raced for 3 months. Postrace concentrations were adjusted relative to albumin concentration to allow for effects of hemoconcentration. Thyroid hormone concentrations were then compared with those of clinically normal dogs of non-Greyhound breeds. Results-When adjusted for hemoconcentration, total T₄ concentrations increased significantly after racing and TSH concentrations decreased; however, there was no evidence of a change in free T₄ or total or free T₃ concentrations. Resting total T₄ concentrations increased significantly when dogs had been neutered and were not in training. There was no evidence that training and neutering affected resting TSH, total or free T₃, or free T₄ concentrations. Resting concentrations of T₃, TSH, and autoantibodies against T₄, T₃, and thyroglobulin were similar to those found in other breeds; however, resting free and total T₄ concentrations were lower than those found in other breeds. Conclusions and Clinical Relevance-Except for total T₄, thyroid hormone concentrations in Greyhounds are affected little by sprint racing and training. Greyhounds with low resting total and free T₄ concentrations may not be hypothyroid.