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Supplements – Decomplexicating Equine Nutrition Part 10 of 12

The nitty-gritty of nutrition seems to lie in supplements which include 1) the elements we call minerals, 2) the electrolytes we call salts, 3) the molecules we call vitamins and 4) the herbs. I hear a lot of people proclaim that paying attention to and supplementing for the lack of these things will enhance the health of the horse measurably. One example of this is the addition of magnesium to help calm the horse.

I have said this several times in these blogs on nutrition and it’s worth repeating here. It is NOT the addition of things that makes the horse healthier. It is the removal of things harming the gut microbes that will turn the health your horse around. Before we go further, let me introduce you to what these things are.


Vitamins are organic (containing carbon) compounds occurring naturally in the foods eaten and several are required to prevent disease in humans. However in the horse, very few vitamins are required due to their very different diet and digestive system. Deficiencies have occurred in some vitamins but only in horses that are starved or have been fed poor quality pasture and hay. This include hay that is over a year old. In other words, if a horse is outside eating good pasture during the growing season and is fed hay during the dormant winter season then there are no known vitamin deficiencies in horses according to extensive research done in the field of equine nutrition.

Yup! All those vitamins you are feeding are not necessary as long as your horse is not experiencing starvation.

The elements that make up all vitamins are the same as proteins: Carbon, Hydrogen, Oxygen and Nitrogen. A few have Phosphorus or Sulfur and one has Cobalt. All of these elements can be found in the foods the horse eats and thanks to the bacteria in the gut and the functioning liver, it is unlikely that horses suffer from vitamin deficiencies unless they are starved.

Vitamin A - Deficiencies have been reported during severe droughts over a long period of time. It is derived from carotene found in plants. Carotene in stored hay will diminish over time. Deficiencies include loss of appetite, night blindness, excessive tearing, thickened corneas and skin, reproductive problems, respiratory problems, seizures, blindness, bone disease and decreased disease resistance. Chronic (3 to 4 months) over-supplementation can cause depression, unthriftiness and death. Prevention is good pasture and hay.

Vitamin D - deficiency is unlikely when fed sun cured hay or they have adequate exposure to sunlight. Deficiency causes loss of appetite and weight loss when deprived for about half a year. Over-supplementation with Vitamin D in horses has been shown to cause several system dysfunctions (bones, kidneys) that can lead to death in 3 to 4 months.

Vitamin E - There are no known deficiencies however in young horses a lack of Vitamin E helps with red blood cell stability. There is some evidence that Vitamin E combined with Selenium may prevent white muscle disease.

Vitamin K - This is not necessary in horses as it is produced by the gut microbes. Vitamin K given at the manufacturer’s recommended dose caused kidney damage in one study with bloody urine formation.

Vitamin B - Additional B vitamins are not needed in the horse due to sufficient amounts in good quality hay and the production of B vitamins by the gut microbes in the hind gut. However, in horses with colon damage (ulcers) or that are stressed, these microbes may not produce enough B vitamins.

B-1 (thiamine) deficiency may occur in horses fed poor quality forage, bracken fern or mare’s tail.
B-2 (riboflavin) deficiencies have not been reported in horses. The one disease associated with a deficiency in the past has now been attributed to another reason.
B-3 (niacin) deficiencies have not been reported in horses.
B-5 (pantothenic acid) deficiencies have not been reported in horses
B-7 (biotin) deficiencies have been shown to cause defects in the surface of hooves in pigs but no requirement has been made for horses.
B-9 (folic acid) low blood levels can occur in horses without pasture but no known diseases.
B-12 (cyanocobalamin) deficiencies have not been produced experimentally in horses

Vitamin C - not a requirement in horses as they produce enough vitamin C in the liver.


Minerals are elements (see the periodic table of elements, also known as atoms) required by horses to perform necessary functions in the body. For example, iron is needed to attach oxygen to the hemoglobin protein within the red blood cell. Minerals cannot be made by the horse and therefore they are considered essential for life and are consumed in the food they eat. The 5 major minerals in humans are calcium, phosphorus, potassium, sodium and magnesium. The remaining minerals are called trace elements and include sulfur, iron, chlorine, cobalt, copper, zinc, manganese, molybdenum, iodine and selenium.

Calcium (Ca) and phosphorus (P) are essential in bone formation especially in young growing horses. While a deficiency in calcium is almost impossible except in extreme cases, phosphorus deficiency can cause a series of problems. Remember ATP in the mitochondria? The “P” in ATP is phosphorus. On the flip side, too much phosphorus actually prevents the absorption of calcium and will cause soft bones (rickets). This is why dicalcium phosphate is added to all grain mixes because all grains, especially wheat bran, are high in phosphorus. This was called “Miller’s Disease” a long time ago when horses were fed the byproducts of the milling industry. Today, wheat byproducts are still fed to horses but because dicalcium phosphate is also added, the disease called Nutritional Secondary Hyperparathyroidism (big head disease, brain disease, miller’s disease), a nutritionally caused calcium deficiency, is avoided.

Magnesium (Mg) is often added by horse owners to calm their horses. A deficiency will cause hyper-irritability, tetany, glazed eyes and collapse so it makes sense to add magnesium to calm the excitable horse. However, the primary cause of magnesium deficiency is the blocked absorption of it caused by excessive feeding of calcium or phosphorus. So if horses are being fed excessive phosphorus from wheat bran and wheat middlings and then more calcium and phosphorus is being added in dicalcium phosphate to counter the high phosphorus, then it would be logical that the horse will become deficient in magnesium. Interesting… This would be an argument to avoid feeding grains with their high phosphorus content plus the added dicalcium phosphate rather than adding magnesium. Maybe this is the primary reason why removing grain from the diet causes horses to settle down quickly.

Potassium (K) - A deficiency in this element is not common in horses but an excess caused by a genetic mutation in Quarter Horses will produce muscle weakness called hyperkalemic periodic paralysis (HYPP).

Sodium (Na) and chloride (Cl) (salt - NaCl) - These elements are everywhere and are necessary for life in all systems within the horse’s body. This is why it is offered free choice to horses. I have rarely seen deficiencies but on occasion I have seen a horse over eat salt devouring a salt block in little time. This causes the horse to drink large amounts of water and urinate a flood of water. I call this kidney medullary washout requiring the normal kidney gradient to be reestablished.

Iodine (I) - Too much or too little iodine in the diet will cause goiter, a term used to describe an enlarged thyroid gland. A third cause of goiter has an unknown cause (idiopathic). In all cases I have seen there is usually being fed a supplement with seaweed, specifically kelp which is high in iodine. Removing this supplement reduces the goiter to a normal size. The horse shows no ill effects from a deficiency or an excess of iodine.

Iron (Fe) - The information about iron is extrapolated from humans and other animals and is presumed to be the same. Iron is conserved by the horse with very little loss with the exception of severe bleeding. This is called efficient conservation and because of this, iron is only absorbed when needed. A deficiency in iron is call anemia which leads to exercise intolerance. Excess iron supplementation (injected, fed or in the environment) can become lethal by replacing other minerals and causing tissue weakness (hemochromatosis, liver disease, diabetes). Older horses may have higher levels of iron due to chronic storing of excess iron. There is a blood test to determine iron levels in the horse.

Copper (Cu) - Deficiencies are not common in horses. It may be part of the development of osteochondrosis in growing foals. Toxicity has not been established in horses.

Zinc (Zn) - Deficiencies are not common but toxicity has been reported in fields located near smelters of metals.

Manganese (Mn) - This is not an essential element but in one case where excessive limestone was added to a hay field, the hay then became low in manganese and the subsequent foals born from mothers eating this hay had severely deformed limbs. However deficiency and toxicity are rarely found in horses fed good quality pasture and hay.

Selenium (Se) - This mineral is low in some soils and a deficiency can be seen in newborn foals as a muscular dystrophy called “White Muscle Disease.” They are often too weak to stand or swallow and die of starvation. Testing and then supplementing the mare before birth will avoid this disease. Deficiencies in horses older than newborns horses have not been shown to cause problems though most commercial feeds add selenium routinely. Toxicity with selenium is more of a concern in the western states in America (Wyoming, Colorado, South and North Dakota, Montana, Utah and Nebraska) because some plants store selenium which are then eaten by the horse. Horse owners living in these areas are aware of this and avoid these plants. Toxicity causes “Blind Staggers” which may include lethargy, unsteady gait, difficulty breathing, diarrhea, increased pulse, respirations and temperature and death. While toxicity is not common in commercial feeds, it is a potential threat to all horses eating commercial mixes. With great sadness, my friend watched 12 polo ponies die a terrible death in front of him after all the horses had been given an IV medicine made with an accidental 10 fold amount of selenium. Care should be taken when feeding anything with selenium supplementation.


Electrolytes are elements that when added to a solvent like water, either lose or gain an electron becoming a charged ion. If a positively charged electrode is placed in one end of the water and a negatively charged electrode is placed in the other, an electric current is created by the charged ions moving through the water to either gain or lose an electron and become balanced (no charge). This is how the nerves, muscles and everything else work in all animals including your horse.

The common elements in horses that can become “charged” include sodium (Na+), chloride (Cl-), potassium (K+), calcium (Ca++), magnesium (Mg++), carbonate (HCO - - -) and phosphate (PO4 - -). The + and - signs after the elemental abbreviation means that the element is in the charged or ionic state. Why is this important in horses? Because the only way to get these elements into a charged state is to keep them apart and separated. This is an activity every cell in the body expends energy on every moment of the life of the horse. It is just like two lovers each in separate rooms; there is great potential but a wall between them. When the potential between charged ions is signaled for and the charged ions come together, an action occurs through this created current by the movement of ions across the wall. Every action made in the body is because a potential between 2 charged ions created an electric current through an opening in the wall between them. Such actions include contracting a muscle, sending a nerve transmission, a heart beat, a thought, the scratching of an itch - everything. These currents are what is measured in the EKG of your heart.

The charged elements are physically forced into the spaces outside the cell (extracellular space) or inside the cell (intracellular space). Na+ is primarily outside the cell and K+ is primarily inside the cell. Their concentrations are precisely controlled in the horse with the gradient between the two constant. The same is true with all ions creating potentials across solid membranes. Whenever ions are allowed to come together, the potential is experienced, the current made and the action occurs.

The main causes of electrolyte loss in horses are extreme sweating and diarrhea. If your horse isn’t sweating (too cold, not exercising) or doesn’t have severe diarrhea, then there is no need to supplement with these elements because there are plenty of these elements in the food they eat. In addition, almost every electrolyte supplement for horses contains sugar in some form which is unnecessary to add to the diet.

Some signs of electrolyte deficiency in horses include muscle cramping (not exertion myopathy which is a genetic disorder), muscle exhaustion (calcium reserves are depleted) and synchronous diaphragmatic flutter (“Thumps” “Hiccups”).

HYPP is an electrolyte imbalance from a genetic mutation occurring in heavily muscled Quarter Horses within a family line. The potassium on the inside of the cell and the sodium on the outside of the cell are allowed to freely cross the muscle cell wall eliminating the potential to make a current and muscle contraction in a thoughtful manner.

Thumps occurs in dehydrated horses when the potential between ions accidentally is triggered by the electric current of the heart beat across the gap between the heart and the phrenic nerve lying across the heart on its way to the diaphragm. As the heart beats, the diaphragm contracts synchronously with the heart beat creating a jerk of the diaphragm (a hiccup) ranging from mild to severe thumping. It is cured with rehydration using electrolyte solution IV.

Herbs and Spices

It has become popular to add herbs (plant leaves or flowering parts) and spices (plant seeds, berries, bark, roots, and fruits) to the diets of some horses usually for a specific benefit. In humans they have shown a beneficial effect on the mitochondria of the cell. The part of these plants being attributed to these benefits are the polyphenols which are a group of plant chemicals that benefit cellular health and in particular, mitochondrial health. Coffee beans have the most polyphenols in human food but many other herbs and spices have them too including oregano, thyme, black pepper, turmeric and others.

There are no bad side effects of adding herbs or spices in moderation and in eastern (Chinese) medicine they are relied upon. Western medicine has not embraced these plant medicines as a form of therapy and I don’t think there are many good and reliable studies done on their use here. But lets look at it another way. Would there be any need for herbal therapy if the horse has a healthy and non-inflamed gut? Ginger helps an upset stomach in humans but why is the stomach upset? Herb and spice plants are found growing in the wild, but not everywhere and not year round. Could there be a lectin or carbohydrate conflict if used indiscriminately?

All herbs and spices are plants and therefore available to the horse if growing in their area. There are no known toxicities when eaten in the wild but some are toxic when given continuously and in excessive amounts for supplementation. The principles of feeding them are similar to all other plants - feed only when in season. Again, in a healthy horse with a normal gut microbiome, there is probably no need to supplement with herbs or spices unless guided by an experienced practitioner for medicinal purposes.


1) Adding vitamins to the horse’s diet is unnecessary unless they are starving or on severely poor pasture and hay.

2) Adding minerals beyond the requirements of the horse may cause health issues. Adding them to pregnant mares and new born foals may be indicated depending on the environment where they live and the quality of forage available.

3) Adding grain, especially wheat, with the addition of extra calcium and phosphorus may cause a magnesium deficiency with irritability as a result.

4) Adding electrolytes is only necessary when the horse is or will become mildly to severely dehydrated through excessive sweating or diarrhea.

5) Herbs and spices have a place when prescribed by a medical practitioner. However in a horse with a normal gut microbiome and not starved, adding these may be unnecessary.

6) Save money by not feeding extra vitamins, minerals, electrolytes or grain. Invest in feeding the best quality pasture and hay you can purchase.

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