Deficiency
Copper deficiency may cause osteochondritis dissecans in growing horses, and it has been linked to rupture of the aorta or uterine artery in adults. It may also cause anaemia and loss of hair pigment [1].
Sources
Many concentrates contain more than 20 ppm copper. In the survey cited by the MSD Veterinary Manual, grass hay averaged 7.9 ppm [1].
Interactions
Excess iron can inhibit copper absorption [1]. Very high zinc intakes, for example from contaminated forage, have caused copper deficiency and developmental orthopaedic disease in young horses [1]. Molybdenum above 15 mg/kg of dietary dry matter may interfere with copper [1].
Excess copper, estimated at 2–3 times the recommended level, may reduce selenium and iron absorption [1].
Ratios
Nutritionists commonly formulate zinc to copper at 3:1 to 4:1 [1]. A&L Canada gives about 3:1 as desirable [2].
Reading it on a label
Trace minerals are reported in parts per million (ppm) [2].
See also zinc, iron, mineral ratios.
Sources
- 1. Liburt NR (peer reviewed by Boyle AG). Nutritional Requirements of Horses and Other Equids. MSD Veterinary Manual, Professional Version. Merck & Co., Inc., Rahway, NJ. Last full review February 2026. https://www.msdvetmanual.com/management-and-nutrition/nutrition-horses/nutritional-requirements-of-horses (accessed 2026-11-07)
- 2. A&L Canada Laboratories. Defining Analytical Constituents in Equine Feed Reports. Fact Sheet No. 234. London, Ontario. Revised February 2022. https://alcanada.com/Tech_Bulletins/Field_Crops/Forages/234-Defining%20Analytical%20Constituents%20in%20Equine%20Feed%20Report.pdf (accessed 2026-11-07)
Last edited 7 Nov 2026, 1:48 am