The effect of ambient temperature on thyroid hormonal and histological changes in sheep

The objective of this study was to investigate the effect of high and moderate summer ambient temperature on thyroid structures and endocrine profile in developing ram lambs. Twenty fall born ram lambs were randomly divided into 2 groups. Animals were kept outdoor (n=10) under ambient temperature (31-50ºC) or maintained indoor (26-32ºC). Daily maximum ambient temperature was recorded for both environments. Monthly serum T3 and T4 concentration were compared between 2 groups throughout the experiment. The animals were slaughtered at the end of the study and their thyroids subjected to histopathological examination. The results showed that maximum outdoor ambient temperature was significantly higher than indoor. There was significant difference between 2 groups on T3 concentration so that in high temperature serum T3 was significantly lower than low ambient temperature. Although there was no significant difference in serum T4 between 2 groups, the concentration of this hormone grossly showed elevation in the group kept indoor. Histopathological examinations of the thyroid revealed the same present of structural changes in both groups. In conclusion, direct exposure of developing lambs to ambient temperature decreases T3 secretion by the thyroid which could have many detrimental effects on lamb performance.