Serum concentration of thyroid hormones in crioula lanada serrana ewes in gestation and lactation

The effects of gestation and lactation on the dynamics of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4) were evaluated in Crioula Lanada Serrana ewes from the plateau region in Santa Catarina - Brazil. To evaluate the effects of gestation, twenty four ewes were randomly divided into groups I and II. Group I was composed of 12 pregnant ewes and the control group (II) was composed of 12 non-pregnant ewes. The effects of lactation were evaluated in the same ewes of group I after parturition (LE) and in the control group (NL). Blood samples were taken in the first, second and third periods of gestation, at parturition, and at 30, 60 and 90 days of lactation. T3 and T4 concentrations were determined by radio-immunoassay (RIA). Pregnant ewes showed lower serum concentrations of T3 and T4 than those of non-pregnant ewes. At parturition, there was no significant difference in T3 concentrations between groups I and II (p>0.05). During lactation, serum T3 concentrations were lower (p<0.05) in LE than in NL ewes. Serum T3 concentrations were greater (p<0.05) at lambing than during the lactation periods. Serum T4 concentrations in LE at parturition did not differ (p>0.05) from those of NL ewes. During lactation, T4 concentrations of LE were lower (p<0.05) than those of the NL ewes. The results of this study have shown that gestation causes a variation in the T3 and T4 serum concentrations, and that lactation results in a decrease of serum concentrations of T3 and T4 in Crioula Lanada Serrana ewes.