Sub clinical zinc deficiency has been suggested to be involved in disease conditions such as broken mouth periodontitis, footrot and mastitis. However, although there is little risk of primary deficiency in the UK. there are large areas around the Mediterranean. Northern Africa and North America that are reported to be deficient in zinc. Therefore a method that could deleiver a long term continuous supply of zinc would be beneficial in these situations. This trial was designed to examine zinc availability from a zinc, cobalt and selenium soluble glass bolus administered to zinc deficient lambs fed on a low zinc diet throughout the trial.