Copper's Impact on Equine Coat Color
Q: Does adding copper to a horse’s diet really have an impact on coat color and protect coats from sun-bleaching?

A: Copper is an essential trace mineral that plays a vital role in many processes within your horse’s body. For example, there are copper dependent enzymes involved in the synthesis and maintenance of elastic connective tissue. Copper is necessary for the mobilization of stored iron in the body and also detoxifies superoxide, a compound deployed by the immune system to kill invading microorganisms.

Coat color is determined by the presence and proportion of melanin pigments. As it turns out, the enzyme responsible for melanin production—tyrosinase—is copper-dependent. This enzyme derived from the amino acid tyrosine results in brown and black pigments. Many coat colors have some level of brown and black in them, including buckskins, chestnuts, bays, and blacks. The latter two colors are also influenced by zinc.

Depigmentation and impaired keratinization of the coat indicate low copper or zinc status. Typically, when copper is low, chestnut coats will appear to have a yellow tone to them and black coats will have a rust appearance. You might especially notice this color shift in a horse’s mane. Coats appear to fade over time due to ultraviolet light causing damage to the pigment leading to color change. If pigment levels are high, coats have greater resistance to damage.

Forages tend to contain relatively low copper amounts, which can leave diets at levels below the Nutrition Research Council’s (NRC) minimum unless they’re supplemented. I suggest feeding 50% of the NRC minimum daily requirement from some source other than forage. For a 1,100-pound horse at rest this is 50 mg of copper and 200 mg zinc. Note that relying on a trace mineralized salt block is unlikely to provide necessary levels.

Unfortunately, it’s not as simple as insuring that the minimum daily requirement is met, as secondary deficiencies can also exist. This happens when copper and or zinc cannot perform normal functions, because they’re interacting with other minerals or compounds that either prevent their absorption or form complexes with them once in the body. Common antagonists of copper include sulfur, molybdenum, and iron. Even when adequate levels of copper exist in the diet these antagonist minerals can cause secondary deficiencies.

Molybdenum doesn’t appear to be as big of an issue in horses as it is in cattle, where it often leads to copper deficiencies. However some water sources can be high in sulfur and iron, and forages also tend to be high in iron. Such issues are typically easy to manage if the diet is supplemented correctly.

So how do you insure adequate copper and zinc in the diet in order to avoid changes in coat color and the less visible problems that can occur when copper status is less than optimal? It might be tempting to think you could just add copper sulfate or other source of copper to the diet. However it is not advisable to add straight copper to a diet, because you might unwittingly cause a negative impact on zinc utilization as high dietary copper is an antagonist of zinc.

A better approach is to feed a commercially fortified feed per the manufacturer’s instructions, or feed a good mineral supplement. A number of supplements claim to darken coat color, and many of these contain copper—and might or might not work. I would argue that coat issues can be an indicator that overall the diet is not as well balanced as it should be and that a solution that supplies a broader spectrum of minerals is a better solution. Paprika is often added to coat supplements or is fed alone as it is thought to aid in coat color. As it happens paprika is a good naturally occurring source of copper. However paprika is also a source of capsaicin, which is a banned substance in competition and best avoided if you and your horse show.

If you’re unsure of whether your horse is getting enough copper, consider finding a qualified equine nutritionist to work with. A qualified nutritionist can evaluate and identify any issues and ensure your horse’s trace mineral needs are met. He or she can also identify and fix any existing secondary deficiencies.