Most of the enzymes in the pig require zinc for their normal structure and function. It forms an essential part of insulin. Pigs deficient in zinc show poor growth, poor appetite and a skin thickening called parakeratosis. Excessive calcium in the diet also reduces the availability of zinc and leads to parakeratosis but the condition in practice is uncommon. The diet should include between 50-100g/tonne. In recent years a new role has developed for the inclusion of zinc in the diet. In the period from weaning to 21 days post-weaning the inclusion of zinc oxide BP (80% zinc) at a level of 3.1kg/tonne in creep diets has been found to have a profound effect on preventing diarrhoea associated with E. coli. Such an inclusion provides 2.5g/kg of elemental zinc and at this level most pathogenic E. coli are inactivated. The mechanism by which this acts is unknown and levels less than this are often not effective. Occasionally the withdrawal of the zinc two to three weeks after weaning can result in diarrhoea and in such cases it may be necessary to continue its use for a further two to three weeks. No adverse effects at these levels have been recorded but a reduction in appetite has been suggested.