RESUMO
The effect of different dietary iodine levels (1 p.p.m.-control, 2 p.p.m. and 3 p.p.m.) on the serum levels of thyroid hormones (T3 and T4) has been studied in gilts at various stages of reproductive cycle, as well as on the their reproductive performances. The gilts were the crossbred of Swedish Landrace x Big Yorkshire x German Landrace, selected for reproduction. The serum concentrations of T3 and T4 in four month old gilts (at the beginning of experiment) were normal: 1.48 +/- 0.28 and 46.57 +/- 11.37, respectively. Approximately the same levels of serum thyroid hormones were found in all 3 experimental groups of the gilts at the first oestrus (about 6.5 months) when they were artificially inseminated, at the end of the first third of the pregnancy, at the end of lactation and on the day of first postlactational oestrus. Significantly lower concentrations of serum T4 were only at 1-3 days before parturition, 6-12 hours after parturition and during lactation in all groups of gilts. There were no significant differences in T3 and T4 concentrations as well as in reproductive performances between gilts on the different iodine diet. The authors concluded that 1 p.p.m. of dietary iodine, which is regularly applied in this pig farm, is sufficient to provide normal levels thyroid hormones and normal reproduction. There is not economical and physiological reasons to increase this level of iodine to 2 and 3 p.p.m., since the obtained results showed that these changes don't demonstrated neither positive or negative effects.
