Trace Minerals: Why They Are Important for Horses

Minerals are so critical to the health and wellbeing of our horses. They help support a wide range of functions, from keeping a horse’s bones strong, to helping produce enzymes and hormones. However, it is a delicate balance. Dangerous deficiencies can occur if underfed. Likewise, if overfed, minerals, and especially the trace minerals, can be toxic and, in rare cases, lead to death. This is why minerals are always a top priority when it comes to feeding horses and why horse owners should be familiar with the various minerals in their horse’s diet.

What Are Trace Minerals?

There are two classes of minerals that you should be familiar with: major (macro) minerals and trace (micro) minerals. The two classifications are in reference to the amounts fed. The major minerals are fed in larger amounts as compared to trace minerals. Regardless of amount fed, both classes are critical to horse health and wellbeing.

The major minerals include calcium, chloride, magnesium, phosphorus, potassium, sodium, sulfur. While much of the historical research was in the major minerals, nutritionists have recognized that trace minerals have just as much of an important impact on horse health and performance. Thus, there has been renewed interest in trace minerals and how much we need to feed each day. Some of the more important trace minerals for horses include:

  • Cobalt
  • Copper
  • Iodine
  • Iron
  • Manganese
  • Selenium
  • Zinc

Horses usually receive most of their daily trace mineral requirements from their forage (hay/pasture). However, there are multiple factors that will impact the level of trace minerals in forage, which has led to deficiencies for horses across much of North America. For example, levels will vary depending on where the forage was grown, which is due to the mineral content of the soil. It will also vary with the species of forage, season of year, as well as other factors. The only way to know the exact trace mineral content of a forage is through a detailed forage analysis.  Other sources of trace minerals in the equine diet include feed, supplements and even the water a horse drinks.

What Trace Minerals Do Horses Need?

It is important to remember that underfeeding trace minerals does lead to deficiencies that can have serious health consequences for your horse. However, and just as important, feeding too much of a trace mineral can lead to toxicity.

Here is a list of the most important trace minerals and why they are essential for your horse.


  • Helps form red blood cells, construction of hair and muscle, and helps regulate the nervous system. Copper is also important to protein (muscle) metabolism and function and bone development in foals. It is also thought to have antioxidant properties.
  • If deficient, horses will be lethargic, exhibit poor performance, and have a poor hair coat.
  • Minimum requirements per day for a 1100 lb horse is 100 mg.
  • Maximum tolerable levels for an adult horse of the same size are estimated at 2500 mg/day.
  • Forages are usually low in copper and require supplementation. Good sources of copper include cereal grains and even dry seaweed. 


  • Helps maintain healthy gut flora and maintains optimal liver function.
  • If deficient, horses may be lethargic, but this is not well studied.
  • The minimum requirements of cobalt in horses have not been widely studied. Nutritionists believe most horses will get adequate levels of cobalt in their diets, regardless of source.
  • Maximum levels of cobalt are currently set at 25 mg/kg of dry matter per day.
  • Good sources of cobalt include cereal grains, alfalfa (legumes), and yeasts. Grass forages and hays can be low in cobalt, requiring supplementation.  


  • Helps optimize thyroid function for basic metabolism. Iodine is also important in brain function and overall body condition.  
  • If deficient, horses can experience hypothyroidism or goitre (enlarged thyroid gland). This can result in poor coats, muscle weakness, hair shedding, and slow growth rates in young horses.
  • Suggested levels of iodine per day range from 1.75 mg/day with light exercise up to 3 mg/day for intensely exercised horses.
  • Maximum ranges of iodine are reported to be 5 mg/kg, or 2.25 mg/lb. of feed, per day.
  • Good sources of iodine include pasture, hay, and iodized salt.


  • Critical component of red blood cells and important for many enzymes.
  • The most glaring sign of iron deficiency is anemia, although deficiencies are rare in horses. Horses suffering from anemia appear listless and suffer from poor performance. They may also have a lack of appetite and appear depressed.
  • Minimum requirements of iron for an 1100 lb horse are suggested at 500 mg per day for light exercise, and up to 1200 mg per day for intense exercise.
  • Fresh forage and hay can be high in iron. Water can also be a source of iron for horses.


  • Important in bone and cartilage formation and strength, cell function, as well as fat, carbohydrate, and protein metabolism.
  • Not well studied in horses, but deficiencies of manganese have led to limb abnormalities in other species.
  • Minimum requirements are generally recommended for adult horses under light work at 350 mg/day. Adult horses in intense work are estimated to require 500 mg/day.
  • Considered the least toxic of the trace minerals, maximum amounts have not been established in horses, nor have toxicities been reported.
  • Forage and cereal grains are good sources of manganese.


  • One of the most well studied trace minerals in horses due to its important antioxidant role in protecting cells and maintaining cellular function. It is also important in muscle and immune functions. Learn more: Selenium: Safe Limits and Testing.
  • Selenium deficiency can lead to poor performance, muscle weakness, lethargy, respiratory distress, and abnormal cardiac function.
  • Minimum requirements of selenium are estimated to be 0.1 mg/kg of dry matter per day. For an 1100 lb horse, this would be about 1.2 mg per day.
  • The maximum suggested tolerable level of selenium for an 1100 lb adult horse is estimated to be 25 mg/day.
  • Forage is the main source of this trace mineral, but can be deficient due to selenium deficient soils, requiring supplementation.


  • Important in respiratory function, carrying carbon dioxide to the lungs, immune function, and can help regenerate cellular damage. It also helps harden hooves.
  • Deficiency leads to reduced growth rates, poor performance, lethargy, and rough hair coats.
  • The minimum requirements for zinc are estimated to be 400 mg/day for adult horses under light work, whereas adult horses under intense work require 500 mg/day.
  • Horses appear to tolerate excess zinc well as compared to other trace minerals. The upper limit for zinc is suggested to be 500 mg/kg (or 227 mg/lb) of feed per day.
  • Pasture and hay are poor in zinc and horses usually require supplementation. Cereal grains, like wheat bran, are excellent sources of zinc.    

How Best to Ensure Your Horses Receive Correct Trace Mineral Amounts

It is understandable that trying to determine how much, or what exactly, to feed your horses to ensure they are receiving the proper amount of daily trace minerals can be audacious. However, because we have advanced so much in our understanding of horse nutrient requirements and feed formulations, owners no longer need to worry. To ensure your horses are receiving adequate amounts of trace minerals, it is generally recommended that they receive a horse feed fortified with trace minerals prepared and manufactured by a reputable feed company. This can be in the form of a ration balancer for easy keepers, like Essential K®, or a full intake feed for a hard keeper, such as Kalm Ultra®. These feeds are fortified with the essential trace minerals all horses need and fills any nutritional gaps left by forage. If you have any questions or concerns on what you are feeding your horse, please feel free to contact us for a free, personalized feeding plan tailored to your horse’s specific needs!


National Research Council. (2007). Nutrient requirement of horses, 6 th rev. ed. National Academies Press.

Pagan, J.D. 2001. Micromineral requirements in horses. InJ.D. Pagan and R.J. Geor (Ed.) Advances in Equine Nutrition II. pp. 317-327. Nottingham University Press. Nottingham, United Kingdom.

Article By: Chris Mortensen, Ph.D.
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