The study was conducted on weaned wistar male rats for the period of 8 weeks from 4 to 12 weeks of age and they were divided into 3 groups as control: rats fed diet without zinc supplementation, Treatment groups, T1 and T2: rats fed diet containing zinc sulphate @ 50mg and 100mg/kg body weight/day, respectively. Blood samples were collected from each rat of all the 3 groups on 6, 8, 10 and 12 weeks of experiment and plasma were separated and triiodothyronine (T₃), thyroxine (T₄) and testosterone levels were estimated. The plasma concentrations of T₃ and T₄ in wistar rats increased as age advanced from 6 to 12 weeks in all three groups. The T₃ values were varied significantly (P<0.01) with each other in different ages; whereas, T₄ levels were recorded significantly higher (P<0.01) at 10 and 12 weeks as compared to 6 and 8 weeks in all groups. Thyroid hormone concentrations were higher in treatment groups (T1 and T2) as compared to control from 8 weeks of age. As compared to control value, in T1 group, T₃ concentration was significantly higher (P<0.01) at 8 weeks of age and significantly higher (P<0.01) T₄ values were recorded from 10 weeks; whereas, in T2 group, T₄ levels were significantly higher (P<0.01) at 10 weeks of age. In between T1 and T2 groups, T₃ concentrations were found higher at 8 and 10 weeks and T₄ values were higher from 8 to 12 weeks of age in T1 group, but the values were not varied significantly. The plasma concentration of testosterone in all groups showed an increasing trend with the advancing age and the values were varied significantly (P<0.01) within the group at different ages. When compared between the treatment groups and control, significantly higher (P<0.01) values were found in both the treatment groups (T1 and T2) as compared to the values of control group from 8 to 12 weeks of age. The present study revealed earlier rise of testosterone in T1 group as compared to T2 group; however, the values were not varied significantly at different ages studied. The study showed that oral zinc supplementation induces a better testosterone and thyroid hormone profile. The concentrations of the hormones in plasma showed an increasing trend with the advancing age.

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