Iodine in the reclaimed upland soils of a farm in the Exmoor National Park, Devon, U.K. and its impact on livestock health

Iodine is an essential micronutrient for animals and humans, yet its behaviour in the soil environment is not clearly understood. This study centres on one farm in the Exmoor National Park. Southwest England, typical of many stock farms in North Devon where livestock grazing upland pastures suffer from iodine deficiency disorders. This area is not characteristic of many other recognized areas of endemic iodine deficiency, in that it is: proximal to the ocean; underlain by sandstones; not enriched in fluorine, calcium or arsenic; and has not been glacially scoured. Iodine deficiency disorders in this area are also a relatively recent phenomenon, associated with improved upland grazing. In addition to the identification of the local sources of iodine, the distribution of iodine btween reclaimed and unreclaimed moorland soils and the differing capacities of reclaimed and unreclaimed soils to retain iodine were also examined. This paper asserts that moorland soil reclamation is an important factor in the aetiology of iodine deficiency disorders in grazing cattle. The processes of ploughing, drainage and liming are thought to reduce the capacity of upland soils to retain iodine in a bioavailable form.