There is a narrow range when supplementing with copper meaning getting it to optimum levels are essential. Sampling can be difficult as bloods can be difficult to interpret and liver samples are the premium method of doing this.
Remember low copper can be an issue but also over supplementation (toxicity) is a big problem on some farms.

It has been associated with swayback and changes in hair coat and wool. It can also when low effect immunity and may cause infertility. As it is involved in glucose metabolism.
While we can get copper deficiencies due to low copper they are rare. They usually occur because of complex interactions or are locked up by other minerals.

The key minerals involved in this are iron, sulphur and molybdenum.