Ingested soil and iodine deficiency in lambs

Abstract

Post-mortem and clinical examination of lambs on the Department of Agriculture Field Research Area at Masterton in 1971 showed that there was a high prevalence of enlarged thyroids in lambs from ewes on low-stocked areas; the condition was almost entirely absent in lambs on high-stocked areas. Faeces from ewes on high-stocked areas which were closely grazed contained substantially more soil than did faeces from ewes on lowstocked areas which had ample feed in winter 1971. Iodine in faeces followed a similar pattern to soil in faeces. Iodine in herbage showed no differences between high- and low-stocked areas. The data suggest that ingested soil was a source of iodine to ewes on high-stocked areas and that this accounts for the virtual absence of enlarged thyroids in the lambs. Possible reasons for the appearance of goitre in 1971 are considered.