The aim of this study was to evaluate the dynamics of triiodothyronine (T3) and thyroxine (T4) hormones, their relation with body condition score (BCS) and reproductive stage of 248 Nelore heifers, and the effect of iodine application on the induction of cyclicity of 217 anoestrus heifers in pasture at the beginning of the reproductive season. At day zero (D0), an assessment of the BCS was performed. An examination of ovarian structures was performed by ultrasound (US) and the serum was collected for hormonal analysis. Anestrous animals received 27 mg of iodine or placebo (saline). After 40 days (D40), another US was performed, and BCS and hormonal determination evaluations were repeated. At D0 and D40, the cycling group had a BCS mean and a T3 concentration higher than the anestrous group. BCS and T3 and T4 concentrations influenced cyclicity and probability of pregnancy. The treatment did not affect cyclicity, pregnancy rate and number of days between the treatment and calving.