Trace minerals are only needed in very small amounts in a horse’s diet. Think milligrams! Despite this, however, the majority of horses still receive too much energy and protein and not enough trace minerals from their diet.
Deficiencies in key minerals over a long period of time can result in a plethora of problems with hoof quality, coat condition, digestion and can also affect the athletic performance of your horse.
This issue stems from the fact that complete feeds are often not well-fortified and are meant to be fed at a rate of 3-5 kg (7-11 lb) per day. Feeding less than this means that the levels of trace minerals that your horse is actually receiving are far below requirements.
Zinc, copper, selenium, manganese, cobalt and iodine are some of the most important trace minerals in equine nutrition. Knowing the basic requirements of each will help ensure that your horse consumes the right amount that it can’t obtain from forage alone.
To prevent deficiencies in your horse’s diet, it is recommended to feed a ration balancer like Mad Barn’s Omneity equine supplement in either premix or pellet form. Omneity is a complete vitamin and mineral formula for your horse that has been expertly formulated to provide everything needed to balance a forage-only diet.
Zinc and Copper
These two trace minerals have similar roles in the horse’s body when it comes to the maintenance and growth of connective tissue and melanin. Proper intake of both zinc and copper is imperative for growing and mature horses, but what is even more important is the balance or ratio of the two.
Horses must consume copper and zinc in proper amounts so that one mineral doesn’t out-compete the other for absorption from the gut. A simple way to monitor this is to keep the Zinc:Copper ratio to between 4:1 & 3:1.
Other trace minerals may be affected as well. For example, excessively high copper intake has the potential to reduce the absorption and utilization of selenium and iron.
Providing adequate amounts of copper and zinc may not be possible when feeding forage alone, and so feeding a well-fortified vitamin and mineral supplement is necessary.
The recommended requirements for a 500 kg (1100 lb), mature horse at maintenance consuming 2% of their body weight in dry matter is 100-120 mg of copper per day, and 400-500 mg of zinc per day.
Iron is an important trace mineral for the functioning of hemoglobin and myoglobin, which are proteins that carry oxygen throughout the body.
Fortunately, iron deficiencies are very rare in horses due to the sheer amount of iron that is usually present in water, forage and most feeds. In fact, our recent review of over 6,500 equine diets found that 99.5% of horses exceed their iron requirements.
Since excess iron is a much more common problem in horses, antagonistic relationships with other minerals like copper, zinc and manganese are of higher importance. For example, high iron intake is known to negatively impact the absorption of dietary zinc and copper.
In addition, free, ionized iron acts as an oxidant, which increases oxidative stress and inflammation. The chronic inflammation caused by these excess free radicals in the body are thought to be implicated in the development of insulin resistance in mammals. 
Generally, only horses that experience severe blood loss, perhaps through a bleeding ulcer, chronic inflammation or heavy worm load, would be ones to watch out for and perhaps need additional iron in their diet.
The horse’s recommended daily requirement of iron is 400 mg.
Selenium is a trace mineral component of glutathione peroxidase, which acts as an antioxidant and is also needed for the functioning of enzymes that produce thyroid hormones- just to name a few (3)! There are over 32 selenoproteins that have been identified, but the function of many is still unknown.
A selenium deficiency can weaken the immune system and cause degeneration of both the nervous and muscle tissue. Toxicity, although uncommon, can cause alkali disease which is characterized by a loss of vision, depressed appetite and/or poor skin and hoof quality.
The selenium concentration of feeds greatly depends on the selenium present in soil, and so this is why certain feeds in certain soil regions (such as Eastern North America) may be more devoid of selenium than others. Because of this, horses that consume a forage-only diet may benefit from supplemental selenium.
The horse’s recommended daily requirement of selenium is 1 mg, however, this is considered the absolute minimum daily intake. 2 to 3 mg is considered optimal and up to 6 mg per day is generally recommended for horses undergoing strenuous exercise on a regular basis. The maximum tolerable intake of selenium is 20 mg/day for a 500 kg horse.
Manganese is a trace mineral that is vital for the metabolism of lipids and carbohydrates as well as the synthesis of chondroitin sulfate in cartilage. A deficiency in manganese may result in abnormal cartilage growth and excess may cause interference with phosphorus absorption.
The horse’s recommended daily requirement of manganese is 400 mg.
As a component of Vitamin B12, or cobalamin, cobalt is essential for the microbial synthesis of Vitamin B12 in the horse’s gut. The replenishment of cobalt for Vitamin B12 synthesis is therefore very important so that Vitamin B12 can fulfill its role in energy metabolism.
The horse’s recommended daily requirement of cobalt is 0.5 mg.
Iodine is an important trace mineral that is essential for the production of hormones in the thyroid that regulate metabolism.  A deficiency or toxicity of iodine presents as an enlargement of the thyroid gland, also known as goiter or hypothyroidism.
The horse’s recommended daily requirement of iodine is 4 mg.
Below is a summary of the daily trace mineral requirements for horses in mg/kg dry matter as well as for a 500 kg (1100 lb) mature horse at maintenance consuming 2% of their body weight in dry matter.
These values are based on the National Research Council’s Nutrient Requirements for Horses (2007).
Keep in mind that these levels change depending on the physiological status of the horse (lactating, pregnant, growing, heavy work etc.) and body weight (Shetland Pony vs. Belgian Draft), which both ultimately influence dry matter intake.
Summary of Daily Trace Mineral Requirements for Horses
The following mineral requirements are based on a mature 500 kg horse at maintenance, consuming 2% of their body weight (BW) in dry matter (DM) per day. 
|500 kg horse||400 mg||400 mg||100 mg||400 mg||4 mg||1 mg||0.5 mg|
Unfortunately, offering a trace-mineralized salt block to your horse with their hay is unlikely to provide these recommended trace mineral levels.
The simplest and best way to ensure that your horse is receiving adequate levels of the most important trace minerals is to feed the recommended amount of a ration balancer or a comprehensive mineral and vitamin formula, such as Mad Barn’s Omneity or AminoTrace+.
Before adding other trace mineral supplements of any kind to your horse’s diet, have your forage and grains analyzed for trace mineral content and seek the advice of an equine nutritionist.
Contact Mad Barn today for a full nutritional evaluation for your horse.
Is Your Horse's Diet Missing Anything?
Identify gaps in your horse's nutrition program to optimize their well-being.
- National Research Council. Nutrient requirements for horses, National Academy Press, Washington, D.C., USA, 2007
- Nielsen, BD., Mandi, MV. and Patricia, MD. A potential link between insulin resistance and iron overload disorder in browsing rhinoceroses investigated through the use of an equine model, Journal of Zoology and Wildlife Medicine 433 (Supplement 3), 61-65, 2012
- Coenen, A. Chapter 10- Macro and trace elements in equine nutrition. In: Equine Applied and Clinical Nutrition. Elsevier Ltd.: 190-228, 2013