Copper is a trace element essential to all cells in the body, but it can become toxic at levels that exceed dietary needs.
Growing Holsteins may be more susceptible to chronic copper toxicity than previously thought. It also is quite possible that toxicity occurs at dietary levels lower than those that induce toxicity in mature Holsteins.
The most recent Dairy NRC lowered the maximum tolerable ration copper level from 100 ppm dry weight down to 40 ppm dry weight based on reports of toxicity.
Read more in-depth information on this subject in this article from the February issue of Bovine Veterinarian, a sister publication of Dairy Herd Management.