Serum thyroid hormone levels in male buffalo calves as related to age and sexual development

A total of 155 male buffalo calves were classified into 17 groups according to chronological age. The body weight was recorded on a balance or computed. Sera samples were analysed for thyroxine (T(4)) and triiodothyronine (T(3)) by radioimmunoassay. Highest concentration of thyroid hormones (T(4), 87.6+/-17.6; T(3), 3.1+/-0.07 ng/ml) were seen during the first week after birth followed by a gradual decline until two months of age. Later, the mean T(4) and T(3) levels fluctuated between 30 and 40 ng/ml and at around 1.0 ng/ml, respectively, except for a mild peak at 12 to 15 months of age. T4:T3 ratio did not vary significantly among various age groups. Both T4 and T3 were negatively correlated with age.