Are you adding a supplement to your horse’s diet that contains iron? If your horse is overweight, diagnosed with insulin resistance, or suffers from equine Cushing’s disease, here’s a word to the wise: You may want to reconsider giving that supplement.

Studies have shown a direct correlation between iron intake and insulin levels in the blood, making it an important factor in managing the diet for these horses.

Iron deficiency anemia is rare and too much iron can potentially lead to laminitis, as well as create an imbalance with other minerals. Furthermore, forages (pasture, hay, hay pellets or cubes) are already high in iron, making supplementation unnecessary and possibly dangerous. To protect your horse, choose a vitamin/mineral supplement that does not include iron and have your hay analyzed.

Calculate the total iron intake in the diet; though an upper tolerable limit for all horses is 500 ppm, it should be far less for sensitive horses. Soaking hay can remove much of the iron, but will also remove other minerals. Balance iron with zinc and copper: iron should not be more than 5 times the level of zinc, and the zinc to copper ratio should range from 3:1 to 5:1.

One more comment: Forages grown from acidic soils will be higher in iron. If you grow your own hay, or can discuss this issue with your hay provider, consider increasing the pH of the soil through lime application.

Juliet M. Getty, PhD, is an independent equine nutritionist. Her research-based approach optimizes equine health by aligning physiology and instincts with correct feeding and nutrition practices. Getty’s goal is to empower the horseperson with the confidence and knowledge to provide the best nutrition for his or her horse’s needs.