Investigation of the effect of age and season on Function of thyroid gland in Arabian male horse

BAKGROUND: Age and season may affect the thyroid gland, which regulates the metabolism of the body.
The experiment was conducted to study the effects of age and season on the concentration of thyroid hormones T3, T4, T3uptake, T3/T4 and free thyroxin index (FTI).
Blood samples were collected from jugular vein of 21 healthy purebred Arabian male horse in summer (July) and winter (January). The male horses were under the same management and feeding program in three age groups 2-6, 6-10 and 10-14 years. After centrifugation of blood samples and isolation of serum, the concentration of thyroid hormones were measured in serum by standard radio immunoassay (RIA) method.
Results showed that there is significant differences in mean values of serum T4, T3uptake and T4/T3 ratio between summer and winter seasons (P>0.05). The concentration of T3 and free thyroxin index (FTI) did not show a statistically significant differences between summer and winter (P>0.05). In summer, the concentration of T4 and FTI value in 2 to 6 years and the ratio of T4 to T3 in 10 to 14 years old males had significantly differences than other ages (P>0.05). In winter, there were not significantly differences for thyroid parameters among various ages of males (P>0.05).
The results of this study showed that under constant conditions, thyroid gland performance may be affected by season and ages in Arabic male horses.