Subclinical selenium insufficiency. 6. Thermoregulatory ability of perinatal lambs born to ewes supplemented with selenium and iodine

Abstract

The ability to resist cold stress was evaluated in 70 perinatal Merino lambs using a partial immersion technique. Their dams grazed pastures low in selenium (Se) and received sodium selenate supplements every 14 days (0-8 mg Se). Half of the ewes also received 100 mg potassium iodide every 14 days from the end of the first trimester of pregnancy. Selenium supplementation of the dam increased blood and plasma Se concentrations in the lamb and reduced thyroxine (T4) and increased tri-iodothyronine (T3) concentrations in plasma. The T4 to T3 ratio declined from 39 to 21 as the Se supplement was increased. These relationships were asymptotic. Selenium status did not affect the time taken for rectal temperature to fall to 35¦C when the lambs were immersed in a water bath of progressively declining temperature, or to rewarm when removed from the water. Lambs born to ewes supplemented with iodide tended to have higher mean rectal temperatures during cold stress but this trend, and most selenium x iodine interactions, were not significant.