Sources
Horses with at least 4 hours of sunlight a day, or that eat sun-cured hay, have no additional vitamin D requirement [1].
Deficiency
Deficiency is rare, but can cause bone abnormalities in rapidly growing foals kept stabled and fed only fresh-cut forage [1].
Toxicity
Signs of toxicity include weakness, weight loss, calcification of soft tissues and blood vessels, and bone abnormalities. As little as 10 times the recommended amount may be toxic, and excess calcium makes it worse [1].
See also calcium, phosphorus.
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)
Last edited 7 Nov 2026, 1:48 am