Thyroxine levels in serum of lambs and ewes were measured to determine their usefulness in assessing iodine nutrition of sheep. Lambs born on properties with no history of goitre had serum thyroxine concentrations more than twice that recorded in their mothers. These high values decreased to a level similar to that in the ewes after 8 weeks. In goitrous lambs younger than 2 weeks old, serum thyroxine concentrations were less than their ewe levels. Lambs born to ewes supplemented with iodine during pregnancy had higher thyroxine levels than lambs of control ewes. A survey of 80 flocks of ewes in Victoria showed that 40% had a low mean thyroxine concentration (less than 50 nmol/l), but only one of these properties had reported an outbreak of goitre. It is suggested that serum thyroxine levels in newborn lambs may provide a more sensitive indicator of hypothyroidism associated with iodine deficiency than ewe levels.
A simple in-vitro test of thyroid function based on the uptake of 131 1-labelled-1-triiodothyronine (Ta) bv an anion exchange resin is described.. Aliquots of serum equilibrated with T 3 are incubated with " Amberlite " resin ; 24 · 7% to 36% of the T is taken up by the resin in the euthyroid state, in hyperthyroidism the figure IS 34 · 5% to 55%, and i~ hypothyroidism it is 16·5% to 26%. In pregnancy the resin uptake is 15·5% to z6%.
Studies have been made on variations in technique.A protein-bound iodine (P.B.I.) estimation is performed on all patients investigated, including those receiving treatment for disorders of thyroid function. Results of both tests are compared.
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