A.You are correct that many horses on forage-only diets benefit from copper and zinc supplementation. This is because the levels of these minerals in forages tend to be fairly low, and it can be difficult to supply the horse’s daily requirements with forage alone if a horse’s intake is restricted.
It’s also important to consider these minerals’ balance and relationship to each other as well as other minerals in the diet. Ideally, the amount of zinc a horse consumes is three to five times higher than the amount of copper. And, even if horses have access to unlimited forage and their basic requirements are met, supplemental sources might still be beneficial to ensure the amounts consumed are properly balanced to each other.
So, what is copper? When I think of copper I immediately think of pipes or wire, and it can be hard to consider this is something our horses require daily. When scientists first found copper in animal tissue, they assumed it was there due to contamination. However, in the late 1920s, they realized, in fact, it is in human and animal tissue because it is a required nutrient.
Copper in the Horse
Copper is an essential cofactor for a number of vital metabolic pathways in the horse’s body; this means that, without copper, certain enzymes are unable to function optimally. Some of the particularly important processes that involve copper are energy production, iron metabolism, connective tissue formation, central nervous system function, and melanin production.
Iron Metabolism—We often think of iron deficiency as being a possible cause of anemia in horses. However, it’s actually likely to be due to a lack of copper, because most equine diets provide significantly more iron than required. On the other hand, copper in forage-based diets is often lacking. Four copper-containing enzymes known as “ferroxidases” oxidize (chemically change when combined with oxygen) ferrous iron to ferric iron, and ferric iron is what’s mobilized from storage to red blood cell formation sites. Therefore, horses consuming copper-deficient diets might lack the copper needed to mobilize iron, resulting in reduced red blood cell formation.
Connective Tissue Formation—Lysyl oxidase is a copper-utilizing enzyme that is responsible for cross-linking of collagen and elastin in connective tissues. Without this cross-linking, the tissues’ strength and flexibility is reduced. Therefore, copper is vital for the integrity of connective tissue as well as the formation of new bone which requires collagen matrix.
Nervous System Function—The central nervous system and brain require copper-utilizing enzymes for normal function. Phospholipids that make up cell walls (include the myelin sheath around nerves) rely on enzymes that need copper for synthesis. And, the dopamine-to-norepinephrine (a neurotransmitter) conversion requires copper-reliant enzymes.
Copper in Horse Diets
The National Research Council (NRC) says a 1,100-pound horse at maintenance requires 100 milligrams (mg) of copper a day. This is a tiny amount but it clearly has significant importance. As work load increases there is a small increase in requirement to 125 mg a day.
Forages provide relatively low copper levels, with most hays providing less than 10 mg/kg which would only just meet the NRC minimum requirement if fed to a 1,100-pound horse at 2% of body weight (22 pounds or 10 kilograms).
The maximum tolerable limit for copper fed to horses is estimated to be 250 mg/kg, meaning our 1,100-pound horse eating 2% of his body weight per day or 22 pounds (10 kilograms) can safely consume up to 2,500 mg of copper a day. Because of this high tolerable limit and the fact that copper absorption can be negatively impacted by a number of factors, it is common for commercial feeds to include copper at levels that will result in a ration that exceeds the NRC minimum requirements.
However, it is important that the horse’s entire ration be balanced, and, for this reason, I don’t recommend adding single sources of copper without the help of a qualified equine nutritionist. To determine whether your horse’s diet is meeting his copper requirement, all sources of copper in the diet need to be accounted.
Other nutrients, such as zinc, that could interact with copper and reduce its absorption also need to be quantified. It is far better to feed a properly formulated balanced feed or supplement to ensure that your horse’s copper requirements are being met than to add single sources of copper.
Ensuring that your horse is consuming enough copper to meet or exceed his NRC copper requirement as part of a balanced ration will go a long way to supporting the health and well being of numerous vital systems.