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Phosphorus

Major minerals stored as g/kg 7 shared products have a value

What it does

Phosphorus is a macromineral; like calcium, its requirement is much higher during growth, late pregnancy and lactation than at maintenance [1].

Imbalance

Excess phosphorus, or a ration with more phosphorus than calcium, can inhibit calcium absorption and cause skeletal abnormalities and nutritional secondary hyperparathyroidism [1]. Horses fed large amounts of grain-based concentrate or wheat bran with grass hay are the most likely to develop a relative calcium deficiency [1].

The Ca:P ratio

Keep calcium above phosphorus: a Ca:P ratio above 1:1, ideally about 1.5:1 [1]. A&L Canada gives about 2:1 as desirable [2].

Forage levels

Forage mineral concentrations depend on soil fertility, plant maturity at harvest and the type of feed [2].

See also calcium, mineral ratios.

Sources

  1. 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. 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