Subclinical selenium insufficiency. 4. Effects of selenium, iodine, and thiocyanate supplementation of grazing ewes on their selenium and iodine status, and on the status and growth of their lambs

Abstract

Merino ewes grazed 3 improved pastures low in selenium (Se) at 7.4 or 14.8 sheep/ha, from mating until their lambs were weaned at about 69 days of age. Treatments were arranged in a factorial design with ewes treated or not with Se pellets, an iodide drench, and thiocyanate given during gestation. Blood Se concentration, plasma thiocyanate, and thyroid hormone concentrations were monitored in ewes and their lambs. Lambs were weighed at birth and at weaning. Mean blood Se concentrations of unsupplemented ewes (Se-) and their lambs were about 0.01 �g Se/mL, and their lambs grew at 144 g/day. Lambs reared by ewes that received Se (Se+) grew at 176 g/day. Se-ewes had lower (P<0.001) circulating tri-iodothyronine (T3) concentrations and higher (P<0.05) thyroxine (T4) concentrations than Se+ ewes, and similar trends were seen in their lambs at birth. There was no evidence of clinical deficiencies of either iodine or Se in any group. Growth rates of lambs were not affected by thiocyanate supplementation of their dams during midpregnancy, but plasma T3 and T4 concentrations were depressed in ewes receiving thiocyanate. Iodide supplementation increased thyroid hormone concentrations in ewes but depressed plasma T3 concentrations in lambs.