Observations on the effects of the administration of thiocyanate and thiouracil to sheep

Abstract

Failure to control the plasma level by renal secretion is the cause of the unpredictable toxicity of thiocyanate to sheep. High levels of methyl thiouracil given to the ewe do not produce goitres in the lambs as large as intermediate levels do. At these high levels iodide may enhance the goitrogenesis, while at lower levels it partially protects against goitre. The relation in time between the radioiodine concentration test and the duration and time of goitrogen administration has a great effect on the result. Previous suggestions that carrier iodide could increase the accumulation of radioiodine in the sheep by overcoming the goitrogenic effect of low levels of dietary thiocyanate are not confirmed. Regular ingestion of thiouracil by the pregnant ewe interferes with the rapid development of foetal thyroid activity found during the fourth month of pregnancy.