The purpose of this study was to measure circulating TSH, T ₄ and fT ₄ concentrations in dogs submitted to a clinical visit for general symptoms (weight gain, polyuria and polydipsia, changes in hair coat). Twenty-eight dogs, 14 cross-breed and 14 purebreds (Golden Retriever, Labrador, Doberman), of both sexes (14 males and 14 females), aged 8 to 14 years, were assessed. No significant differences of circulating TSH, T ₄, fT ₄ concentrations between the baseline and after therapeutic treatment nor between intact and neutered females were observed. Compared to baseline values, intact males showed higher TSH concentrations (p0.01), and castrated males lower TSH concentrations (p0.01) after therapeutic treatment. Compared to intact males, castrated males showed baseline TSH concentrations higher (p0.01), but lower (p0.01) after therapeutic treatment. No significant differences of T ₄ and fT ₄ concentrations between baseline conditions and after therapeutic treatment, nor between intact and castrated males, were observed. The experimental sample considered in this study falls within that casuistry involving elevated TSH concentrations but low serum T ₄ and fT ₄ concentrations or close to the minimum physiological cut-off, in which the common clinical signs suggestive of hypothyroidism was, essentially, overweight and neglected appearance of the hair.

Serum concentration of thyroid hormones in healthy dogs varies according to age, sex, breed or professional activity. The aim of this study was to determine the influence of both age and dogs’ work involvement on TSH and thyroid hormones values. Thyroid-stimulating hormone (TSH), total thyroxine (tT4) and free thyroxine (fT4) were tested in the serum of 57 healthy, German Shepherd dogs. The dogs were divided into study groups according to age: dogs aged 3 to 6 years (A), dogs over the age of 6 years (B) and involvement: police-working dogs (C) and accompanying animals (D). Mean values of TSH, tT4 and fT4 ranged from 0.19 to 0.31 ng/ml, 15.58 to 17.25 nmol/L and 11.83 to 17.89 pmol/L, respectively. The highest values of TSH were in group B and the lowest were in group A, while there was an inverse dependence in case of fT4 concentration. The highest mean values of tT4 were in dogs in group C and the lowest in group B. There were statistically significant differences in TSH (p=0.007) and fT4 (p=0.003) concentrations between the age groups. The results indicate that a dog’s age is an important factor in the case of thyroid profile results interpretation.