Serum concentrations of lipids and lipoproteins and their correlations with thyroid hormones in clinically healthy German shepherd dogs: Effects of season, sex and age

Although there are many evidences regard to the relationship between serum thyroid hormones, cholesterol, triglyceride and lipoproteins in different animals, but there are limited references in dogs. The aim of this study was to determine the correlation between thyroid hormones and concentrations of serum lipid and lipoprotein profiles, and also to detect relationship between the measured parameters in different season, sex and age groups of dogs in Ahvaz district, Southwest of Iran, on 2011. Blood samples were taken from the cephalic vein of 60 clinically healthy and non-pregnant native dogs in two seasons (summer and winter) and in two age groups ( <3 years and >3 years). Sampling was done only once from each animal (30 dogs in every season). The serum concentrations of cholesterol, triglyceride (T.G), very low density lipoproteins (VLDL-cholesterol), low density lipoproteins (LDL-cholesterol), high density lipoproteins (HDL-cholesterol and their correlations with thyroxine (T4) and triiodothyronine (T3) hormones were measured in the studied dogs. The mean serum concentrations of cholesterol, triglyceride, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol (mmol/L), T4 and T3 (µmol/L) were measured in the present survey. The above parameters were also obtained in two summer and winter seasons. Season had a significant effect on T.G, HDL, LDL and VLDL levels in the studied dogs (p <0.05). The concentrations of serum T3 and T4 were lower in summer compared with winter season, without significant difference (p >0.05). No significant differences were detected for the measured cholesterol, T3 and T4 parameters in different age, sex and season groups (p >0.05). To the best of our knowledge, there was no previous research regarding the correlation of the thyroid hormones with the serum lipids and lipoproteins in dogs in Iran. Our results showed that thyroid hormones affect T.G, HDL, LDL and VLDL levels and observed seasonal change in serum may be partly due to changes in thyroid hormones.