Effects of previous experience on total blood and free iodothyronine responses to isolation, restraint and shearing in sheep (Ovis aries)

The aim of this study was to investigate a possible effect on thyroid hormone concentrations in peripheral blood in sheep submitted to isolation, restraint and shearing. Circulating T3, T4, fT3 and fT4 concentrations of No. 40 Pinzirita sheep were evaluated under baseline conditions, 24 h before isolation, restraint and shearing (T0), after isolation (T1), and after restraint and shearing (T2), with respect to the influence of a previous shearing experience (just shorn). A control group of 40 sheep was evaluated under baseline conditions (T0). Two-way RM ANOVA showed a significant effect of previous experience and sex on T3 (P ≤ 0.05) and fT3 (P ≤ 0.01) changes, with lower T3 and higher fT3 concentrations in just shorn than in intact females; on T4 (P ≤ 0.005), fT3 (P ≤ 0.0001) and fT4 (P ≤ 0.001) changes, with higher T4, fT3 and fT4 changes in just shorn than in intact females; on T4 (P ≤ 0.001), fT3 (P ≤ 0.0005) and fT4 (P ≤ 0.001) changes, with higher T4, fT3 and fT4 changes in intact females than males. The magnitude of total and free iodothyronine changes following handling practices suggests that restraint and shearing represent a moderate stressor in sheep, while isolation is probably perceived as a severe stress stimulus.