Calcium to phosphorus
Keep the Ca:P ratio above 1:1; about 1.5:1 is desirable, and foals may tolerate up to 3:1 if phosphorus is adequate [1]. A&L Canada gives about 2:1 as desirable [2]. A reversed ratio can inhibit calcium absorption and cause skeletal problems [1].
Zinc to copper
Nutritionists commonly formulate zinc to copper at 3:1 to 4:1 [1]. A&L Canada gives about 3:1 as desirable [2].
Other interactions
Excess iron impairs copper absorption, molybdenum above 15 mg/kg of dietary DM may interfere with copper, and excess copper may reduce selenium and iron absorption [1].
See also calcium, phosphorus, zinc, copper, iron.
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