TG and disorder of glycogen metabolism: This study aims: (i) to determine the concentration of thyroid hormones (T4, fT4, TSH) in healthy GSD and establish their reference intervals, (ii) to examine the behaviour of thyroid hormones in GSD under different circumstances (e.g., season, type of management, activity level), and, finally (iii) to describe the relationship between thyroid hormone concentrations and body condition score.