Copper is essential to good health and production of your herd and clinical symptoms of deficiency of this trace element include diarrhoea, ill-thrift and anaemia.However, few people see these clinical symptoms in their herd – rather, subclinical copper deficiency is a far more common occurrence – no obvious signs, apart from significant effects on production which are often manifested well after the problem has started. Identification of subclinical copper deficiency is the challenge facing many farmers today and there are different ways of approaching this problem: 1. Many farmers will base their decision on knowledge of the copper status of herds in the district in past years. There are dangers with this approach – except maybe on those farms where the deficiency occurs consistently season after season. Each season differs and so does the amount of copper available for absorption. 2. Pasture sampling to test copper levels in the pasture, and thus predict the probable copper status of the animals is fraught with danger because many variables exist to influence the uptake of copper from feed in the rumen to the bloodstream. 3. Animal sampling – blood tests or liver biopsy – is the best method to monitor copper status of your animals. Blood tests only measure the situation at the time of sampling – it has no value in predicting the future likely status of the animals. Liver biopsy not only gives the status now, but also allows prediction of the future likely requirements of copper supplementation. This is because copper is stored in the liver – the copper present in blood is for immediate use. To get a clearer picture of the herd situation, liver samples need to be taken from enough animals to give meaningful results. Similarly, the samples need to be taken from the class of stock that will relate to the herd or flock. Liver samples can be taken on-farm by your vet from live animals (liver biopsy), or from dead animals at the works.