In order to study of the effects of age, sex, pregnancy and lactation on the concentration of serum thyroidal hormones in clinically healthy Iranian goats, blood samples were collected from jugular veins of 102 native Iranian goats according to their age (<1, 1-2, 2-3, 3-4, 4-5 and >5 years), sex, pregnancy and lactation. Variations in the serum concentrations of T3 (triiodothyronine), T4 (thyroxin), T3 uptake and FTI (Free thyroxin index) were investigated. The concentration of T4, T3 and FTI in different age groups were significantly different (P<0.05). Age had a significant effect on the serum T4, T3 and FTI of the goats, as in advanced ages, these parameters were lower. The concentration of T4 was higher in female animals as compared with males (P<0.05). The concentrations of T4, T3 and FTI were higher in nonpregnant goats as compared with pregnant goats (P<0.05). In contrast, the concentration of T3 uptake was higher in pregnant animals as compared to nonpregnant animals (P<0.05). Lactation had no significant effect on the serum concentrations of T4, T3, T3 uptake and Fl] (P<0.05).
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