Copper was first discovered between BC 3000 and 6000. Like zinc, its uses were centered around constructing metal objects, most commonly in the form of the copper alloys, bronze, and brass.
References to copper in ancient medicinal records indicate that many cultures believed copper had antiseptic properties. Around 1817, scientists learned that plants contain low copper concentrations. This was followed several years later by the discovery of copper in animal and human tissues. However, it was only in 1928 that scientists recognized the essentiality of dietary copper. This finding negated previous assumptions that copper was present in plant and human or animal tissues as the result of environmental contamination.
Today copper is known to function as an essential co-factor for numerous enzymes in the body, which makes it an important mineral, even if only required in trace amounts. These enzymes’ functions are diverse and range from connective tissue development via lysyl oxidase, to antioxidant functions by means of superoxide dismutase, to melanin synthesis.
In the past, the copper status of young growing horses received a lot of interest, as some studies suggested a link between low copper status and developmental orthopedic disease. More recent work in this area has highlighted the importance of total dietary mineral balance, in addition to multiple nonnutritional factors that could be involved.
The current dietary copper recommendation for a mature horse weighing 500 kilograms (1,100 pounds) that is idle or lightly exercised is 100 mg per day. This recommendation increases to 125 mg per day for a 500-kilogram broodmare in the last few months of pregnancy and throughout lactation, as well as a horse with a heavy exercise load.
The copper concentration in common equine feedstuffs varies. In addition, copper metabolism can be influenced by factors such as interactions with other minerals. Excessive dietary zinc concentrations have been shown to affect copper metabolism in weanling foals, but unlike in ruminants, dietary molybdenum has less of an impact on horses.
Commercially produced feeds are balanced to ensure that horses are provided with minerals in sufficient quantities when fed according to the manufacturers’ recommendations. Commercial horse feeds usually contain one or more of the many different forms of inorganic or organic sources of copper available. The maximum tolerable level of copper in equine diets is 250 mg/kg, which is higher than the maximum tolerable level of copper for cattle and sheep. Cattle and sheep are more vulnerable to copper toxicity than horses, swine, or poultry.
It is always a good idea to work with a nutritionist if you would like to add additional supplements to your horse’s diet. A nutritionist can help you to evaluate your horses’ entire diet, ensuring a balanced total dietary mineral intake.
Mieke Holder, PhD, is an assistant research professor within the University of Kentucky’s Department of Animal and Food Sciences.